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Meteorological Concepts for Soaring in the Western U.S.

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1 Meteorological Concepts for Soaring in the Western U.S.
Dan Gudgel Meteorologist/Towpilot/CFIG Meteorological Concepts and Tools for Long Distance Soaring Dan Gudgel NWS San Joaquin Valley Hanford CA

2 Weather Information Sources
Presentation Points Weather Information Sources Meteorology Points Synoptic Scale Weather Patterns A Forecast Funnel Miscellaneous Info Weather Information Sources Meteorology Review Synoptic Scale Weather Patterns A Forecast Funnel Miscellaneous Information

3 1. Weather Information Sources
Weather Data Internet (use “search engines”) Site addresses change frequently for this medium Customize access list for efficient data retrieval Review AC-006, Aviation Weather Review AC-45E, Aviation Weather Services Other Information Sources 1. Internet Notes In the 1950s and 1960s pilots were instructed and tested on their ability to read, understand, and interpret weather information for the purposes of safe flight. With the advent and use of phone systems and FAA consolidation of many weather reporting and briefing sites through the 1970s and 1980s, a whole generation of pilots used only phone briefings to gather weather information despite the continued requirement to understand and interpret weather forecast and observation products. With computer communications and display technology, pilots are once again given easy access to weather products for interpretation. In the soaring community, this information can be utilized to evaluate conditions for quality of soaring flight besides that for safety. There is a lot of pressure to remove free access to weather information on the web. Frequently check your web bookmarks as they are constantly changing or no longer valid.

4 Internet Weather Data Upper Air Temperature Soundings
Observed and Forecast Weather Charts Model Forecasts Satellite Imagery 1. Weather Information Sources: The Internet Upper Air Temperature Soundings Observed and Forecast Weather Charts Model Forecasts Satellite Imagery Education / Explanations Soaring Category Info There are a variety of information sources available. The taxpayer-supported DOC/NOAA/National Weather Service provides the basic informational building blocks of weather data for both the public and private sectors of meteorology. The homepage of the NWS at <> can direct you to “local” weather offices and Centers for Environmental Prediction i.e., Aviation, Tropical, Numerical, etc. But there are a number of fine university and private company websites that also provide basic as well as value-added information, e.g., Dr. John “Jack” Glendening’s (BLIPMAP forecasts and other), FSL and NCAR out of the Boulder, CO, area, and Unisys at <>. A large number of internet sites also provide educational information on aviation weather (or meteorological concepts in general) as well as other explanations. Again, due to the constant change of URL addresses this section of the “Western Weather Tutorial” may become dated rather quickly … we can attempt to update about once per year. In the interim, simply use your search engines available on your web browser software to find. Education / Explanations Soaring Category Info

5 National Weather Service
<> NWS National Homepage Select area of interest (‘clickable’ map) All Western Region NWS Offices listed Numerous weather links Current weather Forecast models Satellite images Aviation Wx Center Other sites National Weather Service (NWS) The NWS provides not only local forecast for the general public but also for various communities, such as aviation, fire suppression, marine, and hydrological. Among the NWS offices, the Reno (REV) Weather Forecast Office (WFO) has been the ground-breaking office for providing soaring forecasts through several decades in the Western Region. Their “Soaring Forecast” product provides basic weather information for several key soaring areas. However, all of the NWS offices provide good quality images for satellite, insights into local area-of-responsibility weather, and numerous links to other data, including radar imagery. There are several WFOs that have been placing some degree of soaring weather information on their websites. With Walt Rogers’ automated thermal soaring forecast product coming on-line, their will likely be improvements and additions to many of these existing sites as well as new forecasts for soaring areas that have not had service until now. For a list of NWS Web Sites in the Western United States, go to: <>. For a list of NWS Offices nationwide, go the NWS homepage at <>.

6 Forecast Systems Laboratory
<> Forecast Upper Air Temperature Soundings 40Km grid resolution Out to 16 Hours Spot forecasts (By airport) Forecast Systems Laboratory This site provides forecast upper air soundings (temperature, dew point, wind) for any given point in the United States. The points may be specified by latitude/longitude or by site identifier (airports, etc.). It is driven from computer modeling.

7 Unisys Weather Upper Air Temperature Soundings
<> Upper Air Temperature Soundings Constant Pressure Charts Model Forecast Charts Education / Explanations Unisys Weather A corporation who is the reference point for many of the internet’s university weather web sites. This site (either directly or indirectly accessed) provides a broad range of weather products. Explanations of an educational nature are provided for many of the images, charts, and text information. Multiple panel forecast charts are provided through this site per Kempton Izuno’s discussion in regard to advance planning for long distance soaring flight (reference: Pacific Area Soaring Council’s 1999 Cross-Country Seminar). While satellite imagery is provided, its resolution is not as high as that obtained through National Weather Service (NWS) web pages.

8 National Center for Atmospheric Research (NCAR) [et al.]
<> Upper Air Data (Temperature/Relative Humidity/Wind Info) Other weather data National Center for Atmospheric Research (NCAR) Provides meteorological information with little in the way of explanations. However, upper data is easy to read and the upper air soundings are a little more timely than the Unisys site (as well as a different format for presentation.) Reference the appendix accompanying this presentation for a list of other Internet addresses (URL). Again, this list is only a quick reference and not intended to exclude any one of the myriad of weather information URLs that are available on the web. These specific sites mentioned in the presentation are mentioned only to give an idea of the diversity and wealth of weather information available.

9 Other Weather Info Sources
For the Aircraft Category Fixed base operators Soaring Society of America Associated sites Other Sources Newspapers NWS Weather Radio FAA DUATS Soaring Information A variety of the fixed base operators are also carrying Internet links to weather sources. Especially those links that provide area soaring forecasts in and around their particular location. Weather information does not have to be categorized as “official” to be of use for the soaring community. Trends of temperatures, as well as satellite information and surface pressure depiction, are often carried in major market newspapers. The National Weather Service (NWS) weather radio channels carry climate information at certain times of the day depending on the local procedures. This information combined with specific forecast information provides the soaring pilot with trends and outlooks. While not as comprehensive but still certainly useful for forecast information and current weather, the FAA Direct User Access Terminal System (DUATS) is yet another source besides Internet access to weather products.

10 2. Meteorology Points Atmospheric Soundings Great Basin Applications
Convection concepts Climate Aspects Local Influences 2. Meteorology Review This section could be considered a little like “Meteorology Course #101” as we review of few weather fundamentals and their application to soaring. For other basic meteorological information, see the FAA’s Advisory Circular AC-006, Aviation Weather. Portions also give an insight into some basic meteorology in regard to some weather phenomena around the inter-mountain West. Atmospheric Soundings Great Basin Applications Convection concepts Climate Aspects Local Influences

11 Sounding Basics Small day-to-day changes can make big
differences in a soaring day's characteristics Spot observation versus need to assess task area air mass, including discontinuity lines Altitude noted by Pressure 850 mb Feet (MSL) 700 mb . 10,000 Feet 500 mb . 18,000 Feet Sounding Basics This slide depicts the altitudes and locations of weather balloon soundings in the state of Nevada. Pilots studying trends in preparation for long distance flying should note what has happened with the weather and soundings from that day; and then evaluate closely the “small” changes from that day as a key to what might be different on the day of flight. The determination of the soaring day, of course, is also in consideration of the bigger, synoptic pattern and surface pressure patterns. Soundings are spot observations. The relevance to an air mass of greater area coverage is aided by other tools such as satellite imagery and synoptic pattern analysis.

12 Sounding Sources University of Utah Upper Air Link Unisys Weather Upper Air Link Sounding Sources These sample URLs link to a couple of meteorological data sources that can provide upper air sounding data, I.e., temperature and humidity plots( degrees C.) versus altitude (expressed by pressure in millibars). University of Utah Upper Air Link (through University Corporation for Atmospheric Research – UCAR) Unisys Weather Upper Air Link

13 Lapse Rate Definitions
While numerous aviation texts reference an “average” atmospheric temperature decrease with altitude (lapse rate) of 3.5 degrees F. (2.0 degrees C) per 1000 feet, this lapse condition is only that, an average. On the other hand, the dry adiabatic lapse rate of 5.4 degrees F. (3.0 degrees C.) per 1000 feet occurs with the physical process of raising a parcel of air in the atmosphere. This cooling rate is a function of a decrease in pressure, and no condensation (or the release of latent heat) occurs within the parcel to “warm” or offset the cooling process. A “dry” parcel rising from the surface will rise at the dry adiabatic rate until condensation occurs (at which time it will then rise at the moist or wet adiabatic rate approximately 2 degrees C. per 1000 feet at lower atmospheric levels) or until its temperature is equal to that of the surrounding air (at which time it no longer ascends).

14 Lapse Rates Dry Moist Adiabatic and 14
The moist adiabatic lapse rate is less than the dry as the heat released from the condensation process slows the cooling. 14

15 Definitions - Stable/Unstable
Dry Atmospheric Conditions + A - Temperature decreasing greater than Dry Adiabatic Lapse Rate denotes unstable atmospheric conditions A B Altitude Definitions of Stable/Unstable Lapse rates (temperatures cooling with altitude) greater than the dry adiabatic lapse rate (depicted by the red line) are considered absolutely unstable with a turnover and mixing of the atmosphere. Lapse rates less than the dry adiabatic rate (depicted by the green line) are marginally unstable and may turn unstable depending on the influences of moisture contributions “warming” the parcel due to the release of the latent heat of evaporation to the extent it has buoyancy. B - Temperature not decreasing as fast as Dry Adiabatic Lapse Rate denotes more stable atmospheric conditions ( d + Temperature

16 Temperature Inversions
Surface-Based and Aloft Temperature Inversions Any time the temperature actually increases with a gain in altitude then an “inversion” condition exists. Temperature inversions can be either surface-based or aloft. 16

17 Wind Shear Wind velocity is a change in speed and/or direction
Temperature inversions are boundaries of air layers Shear zone may not be deep or turbulent but... Each layer of air can have a different characteristics: - Wind velocity - Moisture - Parameter gradients + Wind Wind Shear Temperature inversions can mark subtle boundaries to different wind velocities as the FAA Balloon Category is well familiar. Cold air drainage influences from nearby mountains or higher terrain can delay convective triggers for soaring until such a time that slope heating effects negate or reverse slope wind. Layers of air separated by temperature inversions can have not only different wind velocity (speed and direction), but also different moisture characteristics, and rates of change of those characteristics within the layers or the boundary (inversion) itself. SHEAR Altitude ZONE Wind Temperature +

18 Profiles d d A mixed atmosphere is near-adiabatic (left)
Subsidence from high pressure “caps” convection but high enough to facilitate soaring over terrain (right) Profiles Because of terrain considerations, soaring is generally not considered unless the boundary layer is mixed through at least 4000 feet above ground level (AGL) and needs at least 10,000 feet Mean Sea Level (MSL) to transition to over some of the ridges. For long distance soaring, temperature inversions aloft need to allow thermals to reach at least 13,000 feet MSL for consideration of long distance soaring. Temperature inversions aloft are often the result of high pressure aloft upstream or over the soaring area. Air gradually sinking within the high undergoes compression heating thus resulting in a warmed layer of air. This “cap” results in either the maximum altitude of surface based thermals, or a delay in time as the surface heats further before thermals can ‘break through” and reach higher altitudes. Alt. Alt. d d 18 Temperature Temperature

19 Surface-Based Inversion Established with Time
The night-time temperature inversions are formed as the earth radiates away energy overnight (beginning just before sunset) and subsequently cools the air layer adjacent to the surface. As the night progresses the classic surface inversion gets deeper and stronger. Alt. (0600 LT) 19 (0100 LT) (2000 LT) (1700 LT) Time of Day Temperature

20 Surface-Based Inversion Erosion with Time
Temperature inversions are eroded from below, generally, as the surface heats after sunrise. Alt. Time of Day 20 (0600 LT) (0900 LT) (1100 LT) (1400 LT) Temperature

21 Cloud Base / Moisture Layers
T / DP Closure Possible Cloud Layers Moist Adiabatic Lapse Rate Cloud Base / Moisture Layers In looking at temperature soundings from your weather source, anytime the dew point closes to within 4 degrees C. of the temperature at a given level, cloudiness might be observed or expected to develop with its base at that level (on soundings the altitude is expressed in terms of pressure (see later slide for approximate altitude in feet relative to pressure). Again, once condensation occurs due to a rising parcel, the parcel cooling rate lowers to 2 degrees C. per 1000 feet due to the addition of heat from the condensing water vapor. Therefore weaker lapse conditions at that altitude and altitudes above may now be conditionally unstable due to the parcel rising at a moist adiabatic rate of 2 degrees C. per 1000 feet instead of the dry adiabatic rate of 3.0 degrees C. per 1000 feet.

22 The Drying Process 10000 Ft MSL 5000 Ft MSL Sinking, Heating
Moisture, Deficit Air 10000 Ft MSL Rising,Cooling Condensing The Orographic Drying Process A simple picture illustrates the process by which moisture is depleted from the atmosphere as it rises from the west over the Sierra Nevada … and its impact on western Nevada soaring. This process is applicable to any terrain-induced atmospheric lifting process. As air rises up the Sierra Nevada the moisture in the air condenses, forming clouds, and ultimately raining out the initial moisture. As air reaches the crest of the Sierra Nevada and descends it undergoes compressional heating and drying. A further lift / descent cycle occurs as air passes the White / Inyo Mountains along the South Sierra Nevada. Should moisture and clouds again condense and dissipate over the White Mountains then further drying occurs. After this drying process, the air mass of western Nevada is moisture deficit. The result for western Nevada soaring is that any cumuliform clouds will have cloud bases 3-4,000 feet higher than any cloud bases on the windward side of the Sierra Nevada. Additionally, the lower levels have less moisture so visibilities are very good. This additional airspace below the cloud bases due to the drier air in western Nevada is necessary to allow “comfortable soaring altitudes” for cross-country flight over the high desert valleys and adjacent mountain ranges. 5K Ft Sierra Nevada White Mtns 5000 Ft MSL Owens Valley Great Basin MSL San Joaquin Valley

23 De-Stabilizing Process
Colder Air Advection above, and/or Warm Air Advection below will de-stabilize Delta-T increase! Moisture presence also de-stabilizes De-Stabilizing Process With lapse rate defined as a temperature decrease with altitude, anything that increases that lapse rate can be considered de-stabilizing or making the atmosphere more unstable. That process can occur by the upper level of air cooling and/or making lower levels warmer. As mentioned previously, moisture can de-stabilize the air mass as well. But since soaring flight is concerned with Day VFR flight, I will not generally discuss moisture contributions except to the extent that moisture results in visible convection markers (cumulus to thunderstorms).

24 Basin Thunderstorm / Microbursts
Develop Adjacent cells Classic short duration 60Kt+ Sink Rates Regardless of cell size Wind shifts Degrade ceiling and visibility Thunderstorms represent one of the best of the atmosphere’s severe weather generators. Tornadoes, hail, lightning, heavy precipitation, icing, turbulence, and high wind can all occur with a severe thunderstorm cell. Obviously all of these severe weather occurrences are very dangerous to the aviation community ... but a more insidious aspect can be the threat of high wind emanating from a downburst, a rapidly descending column of more dense air from the thunderstorm cell. For an airborne aircraft, the downdraft speed of a downburst can be of the order of 6000 feet per minute (FPM) or 60 knots. It has been told on more than one occasion of soaring pilots in the Great Basin caught in a downdraft at 14,000 feet MSL and landing within 2 minutes. A microburst is a smaller-time and horizontal scale version of the downburst. With the downburst can come rapidly lowering ceilings and visibilities in precipitation. Not all is “bad” for soaring as the downburst strikes the ground its characteristic upward curl provides a zone of tremendous upward movement. Gliders reaching the edge of the downburst may find themselves in an uncontrollable ascent into cloud base. At the same time visibilities may be lowered along the leading edge of this “gust front” due to lifted dust and sand. This lifting process along the gust front can support convection initiation and subsequently more thunderstorms. Remember the stages of thunderstorm development. cumulus, mature, and dissipating. During the cumulus stage and mature stage inflow (updrafts) often are occurring immediately next to rain/virga shafts. For a single cell, these updrafts may be occurring from all the way around the cell/cloud until adjacent cell growth affects the updraft symmetry.

25 Mojave Desert Downburst
Gust fronts from high-based thunderstorms can result not only in dramatic wind velocity changes but also in degraded visibility from raised dust such as the photograph taken by Cindy Brickner of Caracole Soaring. Courtesy of Caracole Soaring, California City, CA) 25

26 Microburst Sounding Microburst Sounding
This Elko upper air sounding shows a relatively dry air mass at the lower atmospheric levels with mid-level moisture indicated by the dew point closure with the temperature. This provides for a high cloud base around 16,000 feet. With surface temperatures reaching the lower 90s F., convection occurred up to 16,000 feet and then the rising air condensed and triggered thunderstorm development. For the inter-mountain west, this classic “inverted-V” upper air sounding depicts a high potential for a microburst environment.

27 Thunderstorm Activity (#1)
Presence of "cap"; and "penetration" of cap (observed time vs. forecast time?) Winds aloft Cell movement Anvil spread Thunderstorm Activity (#1) (Visible satellite image of August 11, 1998, around 4:00 PM PDT) Ideally for soaring flight, we want convection to occur vigorously in the lower levels of the atmosphere to sufficient altitudes for soaring flight over the Great Basin terrain. Altitudes of 15,000 feet to 18,000 feet MSL are ideal. Of course, higher than 18,000 feet is usually not available due to airspace considerations, and less than 15,000 feet terrain clearance becomes a concern. A “cap” on the convection by a temperature inversion limits vertical motion so that moisture factors do not enter the convection process for thunderstorm development. Of course, thunderstorms will diminish lift potential in a broad area due to precipitation processes, cloud formation shadowing the surface, and limiting lift areas at the cell location with generally sinking air surrounding the cell. The presence of thunderstorms adds an additional factor to the astute cross-country soaring pilot’s decision-making process in regard to routes to fly. It is important to remember the wind aloft direction around 10-15K feet for the direction of thunderstorm movement and the wind direction around 30K feet for any cirrus anvil movement. The resulting sinking air and/or surface shadowing will considerably reduce route options. While the presence of a temperature inversion cap can stop or at least delay thunderstorm development, the pilot must continually evaluate the character and tops of cumuliform clouds relative to the inversion altitude. For example, cumulus clouds remaining quite formed up to and well into the inversion early in the day may indicate the inversion will be eroded and that thunderstorms will be likely in the afternoon with so much more heating yet to occur.

28 Thunderstorm Activity (#2)
Air mass Thunderstorms Favored spots Outflow Thunderstorm Activity (#2) (Visible satellite image of August 11, 1998, around 4:00 PM PDT) In consideration of favored air mass thunderstorm locations, return routing or timing may be altered to avoid being caught away from the return point. There are generally favored thunderstorm locations in many areas around the country. As an example, with no forcing mechanisms such as convergence or widespread moisture fields along the Sierra Nevada Mountains from Truckee, CA, southward, favored locations are: Mt. Siegal (southeast of Minden); Mt. Patterson (north of Bridgeport); Mt. Leviathan (northwest of Bridgeport); Mt. Grant (east of Flying 'M'); Mt. Whitney (west of Lone Pine); Split Mountain (northwest of Independence); Mt. Warren/ Mt. Dana (west of Mono Lake), Olancha Peak (southwest of Owens Lake...but not usually a problem area), and Mt. Rose (southwest of Reno...affects last of flight into Truckee and Air Sailing).

29 Radar Radar Doppler Weather Surveillance Radar (WSR-88D) image of rain and snow shower activity as seen from the NWS Salt Lake City weather radar for February 17, 2000, at 1640Z. This image is downloaded from the internet through the “Intellicast” commercial vendor. Since January 2001, radar information is available through both NWS Internet Websites as well as commercial company sites.

30 Classic Supercell Thunderstorm
Light Rain Moderate/Heavy Rain & Hail Gust Front Hook echo Hook echo Anvil Edge Severe Thunderstorms This image is a conceptual model of a severe thunderstorm. Reference the thunderstorm as if it were moving northeast (a favored direction for severe cells). If you were the cell, the right rear quadrant of this cell is where the severe weather often occurs, i.e., tornado, hail, and the damaging high winds emanate. The cirrus anvil is spread out to the northeast. Lift might be found, if you have any altitude between terrain and cloud base, along the depicted meso-scale fronts. But large areas of cloudiness and areas of slowly sinking air around the cell do not make this a desirable, planned lift source for soaring flight. Gust fronts can provide tremendous lift but it may be unmanageable due to lowered cloud bases let alone the dangers associated with the cell itself. Generally, thunderstorms are to be avoided not sought. Further explanation on supercell thunderstorms…(compliments of the DOC/NOAA/NWS Storm Spotting Training material) On the left we see a top view of a supercell while on the right is a radar view showing precipitation location and intensity. The center of the mesocyclone circulation is denoted by the green circle on the left and the white circle on the right. The leading edge of the rain-cooled downdraft air is denoted by the cold front or gust front. The counterclockwise rotation of the mesocyclone and a smaller scale downdraft on the southwest or west side of the thunderstorm produces the hook appearance as precipitation is wrapped around the southwest portion of the circulation. (Diagram adapted from C. A. Doswell III, 1985: The Operational Meteorology of Convective Weather. NOAA Tech Memo ERL ESG-15.) Reference the thunderstorm as if it were moving northeast (a favored direction for severe cells). Down to the south and southeast of the cell is an extending, flanking line. Ahead of this flanking line and to the east of the cell are general areas of lift. As mentioned, though, cirrus and other areas of sink around the cell are not consistently conducive for soaring flight … especially if there are other cells in the vicinity to complicate the flow patterns. Supercell Thunderstorm (top view) Nautical miles 5 10 WSR-88D Radar Image 30 National Weather Service

31 Convection Circulation
Temperature Differences Uneven heating leads to differing air density and ultimately supports a thermal circulation Terrain/slope contributions Surface heating capacity = f(ground and lower air mass moisture content) Convection Circulation Given no large-scale pressure patterns influencing air movement, different rates of heating the surface will lead to differing air densities adjacent to the earth’s surface subsequently supporting a convection process subsequently moving the air. The surface heating capacity is a function of several items but moisture plays a very important role. Since water has a tremendous heat storage capacity before its temperature will rise, the presence of moisture in either vegetation or water will delay the convection process due to the delay in temperature rise.

32 Elevated Thermal Source
Great Basin Mountains Mountain slopes normal to incoming energy Less attenuation Air density Moisture Pollutants Less mass of air to heat for greater buoyancy Elevated Thermal Source This slide describes one of the factors that enhance thermals (convection) in the inter-mountain West, the elevated thermal source. The incoming of the sun is most efficient in areas such as the Great Basin in the West for the following reasons: 1) The slope of the mountains increases the angle at which the sun’s energy hits the surface and allows more energy per unit area (and a greater heating rate); 2) The height of the terrain into the atmosphere is relatively high (mountain tops from 10,000 feet to 14,000 feet millibars to 600 millibars of pressure). This places already 1/4+ of the atmosphere’s mass below the altitude of the thermal source. Therefore there is less atmospheric attenuation of the incoming energy from air mass, moisture, and many man-made pollutants. The geographic location of the Great Basin downstream of the moisture depleting Sierra Nevada Mountains also allows for an efficient dry heating of the surface; and, 3) Because the air density is less at higher altitudes, the mass of air to be heated adjacent to the surface is less than a similar volume at higher pressure (lower altitudes). Therefore, the effective temperature of the “mountain tops” is higher than a dry adiabat from Great Basin valley surface temperatures might depict...on the order of about 2 degrees C.

33 Climate and Other Influences
Climate and Terrain Considerations Modifying Influences and Contributions Thunderstorm Indices Climate and Other Influences This section continues to discuss the unique combination of Great Basin characteristics, along with some meteorological indices, that affect soaring in the intermountain and desert portions of the western United States.

34 Climate and Terrain Time of year Humidity factors
Great Basin Time of year Diurnal temperature spread Humidity factors Terrain rising aspects (and TAS) Climate and Terrain The Ely, Nevada, temperature versus the time-of-year depicts the peak in temperatures in the July time period (and is similar to all Great Basin locations ). The peak in incoming solar energy occurs in late June with the highest sun angle and longest days (next slide). But heating and drying are normally still occurring through June, so therefore the best surface heating efficiency is normally reached in the July time period. Late spring rain/snow or the cessation earlier than normal cool season rain/snow can impact the time of this peak . Further study regarding the occurrence of wet El Nino years or dry La Nina years could give some clue to a variation in this peak of heating. Dew points are normally around 30 degrees F. in the heat of the summer except when moisture surges occur or in immediate proximity to one of the few lakes around the Basin. The combination of dry mountains and high basin valleys allows for flights to be conducted in low density air. Therefore high true air speeds (TAS) and subsequently high ground speeds are attainable and allow for longer distance flights given similar atmospheric lift capabilities at lower altitudes. Taking advantage of thermals going higher from elevated thermal sources, flights from Minden southeastward toward the Sierra Nevada and White/Inyo Mountains are able to “step up” due to the average rise in terrain height.

35 Sunset / Sunrise / Normal Temps
Reno, NV Sunrise / Sunset June 1 5:34 AM PDT / 8:20 PM PDT July :35 AM PDT / 8:30 PM PDT Aug 1 5:58 AM PDT / 8:12 PM PDT Sep 1 6:27 AM PDT / 7:30 PM PDT Normal Maximum/Minimum Temperatures June / ()T=37.2F) July / ()T=41.7F) Aug / ()T=42.5F) Sunset / Sunrise / Normal Temperatures Reference for length of day from June 1st to September 1st at Reno, NV. Also the average diurnal spread of temperature between minimum and maximum for Reno, NV, for the months of June, July, and August. Note that the longest days of the year are late in June (near July 1st) with close to 15 hours of daylight but that the ground is still in the drying process as diurnal temperature variations have not yet reached their peak. The combination of still relatively long days and dry ground makes July up through early August an optimum time for a lot of long soaring cross-country flights.

36 Great Basin Temps Great Basin Average Delta-Temperatures For the month of July around the Great Basin, the average daily diurnal temperature variation (delta-T) reflects the relatively dry air mass of the area. Note that Reno ranks as one of the larger delta-T locations. This large delta-T is due to the smaller, enclosed basin of the Truckee Meadows (and the Carson Valley for Minden) cooling dramatically at night due to mountain slope cooling effects and then heating with incoming solar energy the next day. Larger basins or plains, such as that at Tonopah, or the windier locations such as Tehachapi, do not have as large an average delta-T due to this lack of pooled, slope-cooled air. Yet this climate characteristic of a large delta-T, reasonably good everywhere in the Great Basin area, can be indicative of excellent soaring characteristics. It reflects minimal moisture so that energy translates into sensible heat rather than latent heat in moisture. That incoming energy effectively and quickly heats smaller volumes of air in the smaller valleys or air basins for early convection during a soaring day. It is important to note what the average delta-T is for a location, however, in planning purposes. Any temperature trend toward larger-than-average delta-T for an area would likely be indicating better-than-average convection initiation (thermal development) for that site.

37 In another pictorial presentation format, the average delta-T (change in temperature) between the maximum and minimum temperatures is presented for July (averaged from the years from 1960 through 1990). The Y-Axis lists selected locations in the Inter-Mountain West. The X-Axis (from left to right) is marked for degrees F. of average change between the maximum and minimum temperature for the July Time Period. Note the consistency of the geographic locations in Northern and Central Nevada to provide high diurnal temperature variations. Remember this is indicative of the general lack of atmospheric and surface moisture, tremendous heating capability due to terrain orientation, small air basins that have the capability to trap cold air from drainage at night, and minimal wind mixing. 37

38 The Drying Process 10000 Ft MSL 5000 Ft MSL Sinking, Heating
Moisture, Deficit Air 10000 Ft MSL Rising,Cooling Condensing The Orographic Drying Process A simple picture illustrates the process by which moisture is depleted from the atmosphere as it rises from the west over the Sierra Nevada … and its impact on western Nevada soaring. This process is applicable to any terrain-induced atmospheric lifting process. As air rises up the Sierra Nevada the moisture in the air condenses, forming clouds, and ultimately raining out the initial moisture. As air reaches the crest of the Sierra Nevada and descends it undergoes compressional heating and drying. A further lift / descent cycle occurs as air passes the White / Inyo Mountains along the South Sierra Nevada. Should moisture and clouds again condense and dissipate over the White Mountains then further drying occurs. After this drying process, the air mass of western Nevada is moisture deficit. The result for western Nevada soaring is that any cumuliform clouds will have cloud bases 3-4,000 feet higher than any cloud bases on the windward side of the Sierra Nevada. Additionally, the lower levels have less moisture so visibilities are very good. This additional airspace below the cloud bases due to the drier air in western Nevada is necessary to allow “comfortable soaring altitudes” for cross-country flight over the high desert valleys and adjacent mountain ranges. 5K Ft Sierra Nevada White Mtns 5000 Ft MSL Owens Valley Great Basin MSL San Joaquin Valley

39 Major Modifying Influences(#1)
Washoe Zephyr Nevada Sinks Mono Lake Shear Basin Air Terrain "Holes" Major Modifying Influences(#1) While the resident air in the Great Basin and other basins in the West generally have good soaring characteristics, there are factors that influence the soaring characteristics locally around the Great Basin, as an example. Some of those influences are: 1) Washoe Zephyr (afternoon surface west winds) originating from the cooler, denser air around Lake Tahoe (pulled into the western valleys of the Great Basin from the establishment of a thermal low during the course of the day’s heating); 2) Mono Lake Shear (again the influence of more dense air around Mono Lake offset to the east-northeast by local convection circulations); 3) Basin air pushed up and modified from the coastal valleys of Southern California and even the Southern San Joaquin Valley stabilizing the air in the southern end of the Inyo Mountains and Southern Owens Valley. Even if the flow is not extensive, the lower elevations of the Inyo Mountains will be washed out and devoid of thermals; 4) Sinks of the Great Basin that capture what little surface water is available. Even though standing water is not always present, the subsurface does contain some moisture again robbing the surface of higher sensible heat, e.g., the Carson Sink; and, 5) Terrain “holes”: —Lower terrain that demands higher surface temperatures to provide the same kind of maximum thermal altitude as surrounding mountains or valleys (and usually do not due to energy attenuation and other previously listed effects, e.g. Death Valley, Saline Valley); —Upstream lake influences such as Walker Lake on the Hawthorne area, Pyramid Lake on Wadsworth/Fernley, and the Great Salt Lake around the east-northeast corner of the Great Basin.

40 Major Modifying Influences(#2)
Topaz Flow Mammoth Lakes June Lake Major Modifying Influences(#2) Besides the previously mentioned air mass modifying influences, a rather consistent subset of convergence lines or areas similar in mechanism to the “Washoe Zephyr” exists along the east side of the Sierra Nevada in eastern California and western Nevada: 1) Topaz Flow: Southeast of Minden a “convergence” line sets up due to the confluence of the Washoe Zephyr and flow from local wind influences in and around Topaz Lake; 2) Mammoth Lakes: From Mammoth Pass air flow moving east and then turning toward the south interacts with up-valley southerly flow from the Owens Valley and develops an area that tends to favor thermal development. Rather than an organized convergence line due to the disruptive effect of terrain frictional influences, the location of this convergence “area” will vary depending upon the strength of the Owens Valley flow; and, 3) June Lake: Like the Mammoth Lakes area but rather due to air turning northward from Mammoth Pass, an area of lift from upslope and up-valley flow favors an area of lift in the vicinity of June Lake north of Mammoth Pass.

41 Favorable for Great Basin Soaring
Pressure Patterns Favorable for Great Basin Soaring High location (aloft) Ridge aloft east of task area (or far west) Low pressure (aloft) Not strong or close enough to bring strong gradient wind De-stabilizing Influences Split flow in the upper wind field with weak trough Allows for Instability aloft but good surface heating Thermal Trough (surface) Through interior CA (better if along the coast!) Pressure Patterns Meteorologically high pressure right over or immediately to the west of the desired flight area is not ideal due to strong subsidence (or sinking air) aloft. Often in such a situation the temperature inversion cap is at or below 14,000 feet MSL and that subsequently inhibits strong, consistent thermals to high enough altitudes to encourage the longer basin flights. Some of the factors that have been observed to support good thermal generation are the presence of weak low pressure aloft. This low would have lighter wind flow due to its associated weaker height gradient aloft (winds less than 20 knots through 15,000 feet MSL.) thus allowing good surface heating with no little cloudiness and minimal dissipation or shearing of thermals. At the same time the cooler air aloft with the low center or trough axis provides one of the components of de-stabilizing the atmospheric lapse rate. The location of the surface thermal trough through Central California’s Central Valley or farther west provides the positive pressure gradient from the Great Basin to the west and south thereby suppressing the intrusion of stabilizing air into the western valleys of the basin.

42 Pressure Gradients(#1)
Stable Air Movement to the Western Great Basin Great Basin to Interior California 4 mb Reno to Sacramento delta-P inhibits Washoe Zephyr development Pressure Gradients(#1) Again, there are numerous factors that can modify or weaken the better soaring characteristics of the Great Basin air mass. What does it take to bring these characteristics into effect or minimize them in the Great Basin soaring area? The key is in the location of the surface thermal trough. There are a few key indicators that a soaring pilot should look at to help determine what might bring more stable air into the task area based on pressure patterns. From basic meteorology, remember that the larger the pressure difference between two locations, the higher the resulting wind between those two locations. Note: Look at the Reno to Sacramento pressure gradient (delta-P). A rule-of-thumb by Doug Armstrong is looking at the difference in the Reno and Sacramento (or interior valley of California) surface pressure. A delta-P of 4 millibars (Reno higher than Sacramento) will likely eliminate or effectively delay the onset of the Washoe Zephyr through the Minden area and other western Basin locations. Some value between 3 to 4 millibars will effectively delay the onset until late in the day, and delta-P values less than 3 millibars simply inhibit but not usually eliminate the zephyr during the summer months. In the West, the presence of any large bodies of water westward of a given site will tend to weaken thermal activity until some distance downwind where soil temperatures again reheat the lower atmosphere.

43 Pressure Gradients(#2)
Stable Air Movement to the Western Great Basin South CA Coast to Desert Interior Depth of marine layer greater than 1500' MSL 3+ mb Los Angeles (LAX) to Daggett (DAG) Central CA Coast to Desert Interior 6+ mb San Francisco to Las Vegas Depth of marine layer greater than 2000' MSL Pressure Gradients (#2) 2) Stabilized air pushing in from the southern California coast will produce active shear lines in the Mojave Desert area. Normally these shear lines will not be active if the marine temperature inversion along the south coast is less than 1500 feet MSL. When the Los Angeles to Daggett pressure gradient reaches 3 millibars or greater and the marine layer is 1500 to 2500 feet, very good soaring along shear lines is present in the Mojave Desert. If the onshore push of marine air gets stronger due to higher pressure gradients and/or the marine layer climbs above 3000 feet MSL, a major push of air develops all the way through the Mojave Desert and up the Owens Valley. Subsequently, thermal development along the base of the Inyo and White Mountains is suppressed along with the strong southerly flow through the Owens Valley; and, 3) The San Joaquin Valley is likely to push modified and more stable air into the Southern Owens Valley when the San Francisco to Las Vegas delta-P is greater than 6 millibars and the depth of the marine layer along the Central California coast is 2000 feet MSL or higher.

44 Thermal Detractors <Cirrus Anvil from Thunderstorms <Cirrus
Macro-scale Level <Cirrus Anvil from Thunderstorms <Cirrus Around jet stream cores Small pressure perturbations / waves <Convective Cloud Cover More than 50% sky cloud cover <Other Relative Humidity gradients Thermal Detractors 1) It is important to note the upper level winds, especially around the 30,000 foot MSL level, prior to any flight in the western United States. While thunderstorms indicate an atmosphere capable of supporting soaring flight, the cirrus anvils from thunderstorms shade tremendous areas thus reducing or eliminating thermal development in those areas. The direction of wind aloft gives the pilot where lift may be suppressed from thunderstorm cirrus anvil shading. 2) Cirrus also shades the earth and reduces the energy at the surface to generate consistently strong thermals. Besides the development from thunderstorms, cirrus can form with only mild changes in either pressure or humidity aloft. Due to the relative insensitivity of humidity sensors compared to the relatively minor changes in humidity necessary to generate cirrus cloud fields, cirrus is very difficult to forecast. Pilots need to remain vigilant in the course of their flight for any high cloud development. 3) Thermals begin to diminish in frequency and strength when the convection process covers too much of the sky. The ground shadowing from cloud cover greater than 50% begins to cut-off thermal development. However, by understanding the lift processes around cumulus clouds and virga, cross-country flight can be extended beneath such cloud “over-development.” 4) Areas with a lot of moisture can begin to impact the ability for the ground to heat. Therefore, thermal strength with a lot of ground moisture, like over-development, is weakened compared to the typically strong western U.S. lift rates. On the other hand, moist lower levels of the atmosphere with drier air overhead provide inhancement to the thermal strength.

45 Thermal Enhancers <Rising terrain steps to southeast of Minden
Great Basin <Rising terrain steps to southeast of Minden Minden to Patterson/Bridgeport +2000' Patterson to Whites +1000' and more <Convergence / Shear Mono Lake Shear Line Flying “M” Shear Line <Small air basins Fixed volume of air to heat (valley vs. plain) <Other Summer wave or wave-encouraged cloud streets Thermal Enhancers The terrain rises in steps from Minden to the southeast. From Minden to the Patterson/Bridgeport area, the terrain, valleys and mountains, rise about 2000 feet; and from Patterson to the White Mountains another rise of feet occurs. This enables the elevated heat source effects to provide better thermal consistency and strength once the pilot begins the cross-country flight. While not comprehensive, there are a couple of prime examples of shear and/or convergence line development from mountain-valley or air mass discontinuity that pilots should recognize as thermal enhancing. Specifically, the air moving off Mono Lake and east-northeastward provides lift along the air mass discontinuity (or shear) line. However, remember the air coming off Mono Lake, and like any other body of water, is stable behind such lines with little in the way of thermal activity. To overshoot the shear line and end up well into the stable air will result in a landout! Similarly, afternoon up-canyon northwest breezes will often converge in the Flying M area enhancing thermals in the vicinity. Comments have already been rendered in a previous slide about the benefit of smaller air basins providing smaller volumes of air to heat for quicker, consistent thermal development compared to their larger neighboring basins or plains. Other thermal lift enhancement can come with increasing westerly flow aloft and a tendency for a summer “mountain wave.” Sometimes the surface and lower atmospheric levels will still heat sufficiently for thermal development, but there will be a tendency for thermal lift to form in lines roughly parallel to the ridges (enhanced by the mid-level lifting process associated with wave-like conditions). This is a bit different than a classic mountain wave which can occur given the proper conditions and weather system strength. The conditions of “warm season” mountain wave have been seen infrequently and pilots should be aware of the possibilities, but this phenomenon will not be discussed specifically other than this reference.

46 Mojave Desert Shearlines
Wind through the mountain passes adjacent to the Mojave Desert brought on by thermal induced pressure differences results in convergence (or shear lines) in the Mojave Desert. 46

47 Mono Lake Shear Line Mono Lake Shear Line “Typically” present
Example: 6/13/99 Mono Lake Shear Line … June 13, 1999 … Synoptic Situation A developing trough off the California Coast began to support southwesterly wind flow aloft into California. As the day progressed the western portions of Nevada more strongly came under the influence of the trough as well. While the western Nevada skies were essentially clear, the lifting process associated with a “shear line” and just enough moisture from Mono Lake or residual low level moisture ahead of the trough, provided for a “marked” Mono Lake Shear Line. Numerous and favored shear line locations are prevalent in the deserts and mountain areas and are known by the experienced, long distance, cross-country soaring pilots. In flying the Great Basin area, analysis of current wind flows (observed by pilot or automated stations) can give important clues to the locations of lift in either shear lines or enhanced thermal areas. Prior to the event High Pressure had been present over and just east of Nevada with very light, westerly wind flow aloft. Temperatures were seasonal with the mid to upper 80s F. noted over much of Nevada. Surface pressure patterns indicated that “normal” afternoon west winds were likely for western Nevada valleys. Visible convection around Mt. Patterson as denoted by satellite imagery began around 1 PM PDT. 47

48 Mono Lake Shear Line Visible Satellite Imagery for 530 PM PDT 6/13/99 (0045Z 6/14/99) A look at the visible markings of the Mono Lake Shear Line late in the day. As the day had progressed west wind flow through Tioga Pass, west of Mono Lake, passed over the lake and had sufficient moisture to “mark” the presence of the lift with cumulus in the developed shear line. Again, the typically dry southwest flow over western Nevada and the Southern Sierra Nevada brought little other cloudiness except for this lifting process along the shear line. 48

49 Mono Lake Shear Line Visible Satellite Image for 2130Z 6/13/99 (230 PM PDT) Note that convection had already begun to develop some cloudiness around Mono Lake no doubt from elevated heat sources by 2:30 PM PDT. Noted for early activity, Mt. Patterson environs are already showing well developed cumulus. Little else in the way of cloudiness is seen in the area to the north and east of Mono Lake with the “dry” southwest wind direction over western Nevada during this time period. Note the total time from its inception at Mono Lake to the ring pushed well to the northeast was only about 4 hours (1:45 PM to 5:45 PM PDT.) 49

50 Flying “M” Shear Line Flying “M” Shear Line “Typically” present
Example: 6/14/99 Flying “M” Shear Line … June 14, 1999 With a trough continuing to develop along the California Coast but not progressive, or eastward moving, during this day, wind flow aloft was southwest but relatively weak over western Nevada. High pressure aloft remained in place over Nevada with surface pressure gradients supporting westerly wind flow in the valleys during the afternoon. Reno reached a high of 89 degrees F. after a morning low of 55F. Another such shear line frequently sets up in the vicinity of Barron Hilton’s Flying “M” Ranch during the early afternoon hours. This shear line is the result of up-valley wind from the northwest as it interacts with the higher mountains south through the Flying “M” headquarters. It is generally along an east-west axis. 50

51 Flying “M” Shear Line Visible Satellite Image for 330 PM PDT 6/14/99 (2230Z) Shear line presence is shown by a few cumulus markers on this 330 PM PDT satellite image. Note the the north-south line well east of Mono Lake and another line running east-to-west from south of Walker Lake and south of the Flying “M” Ranch headquarters. This is a favored location for early afternoon thermals for pilots. On this particular day, little else was noted in the dry flow aloft over western Nevada except for the presence of the two marked shear lines. The early development (often by 1 PM PDT) of the shear line south of the Flying “M” is likely a function of winds up from the Bridgeport area and interacting with air from the Smith Valley and later in the day from the up-valley wind through the Flying “M.” The development of the north-south line southeast of Flying “M” and over the Lucky Boy Pass area also represents interaction from wind from the southwest from the Southern Sierra and the different air mass in Central Nevada. 51

52 Flying “M” Shear Line Visible Satellite Image for 5 PM PDT 6/14/99 (0000Z 6/15/99) With time, the cumulus markers for the shear lines under discussion have enhanced while few other cumulus are noted in the western Nevada area. With the incoming upper air trough and falling surface pressures over central Nevada, southwest wind up from Bridgeport and south wind from the Owens Valley continue to support the shear lines late in the afternoon on this day. The western valleys of Nevada are likely having moderate afternoon west winds. Note the cloud streeting present over east-central Nevada as some slight moisture increases at lower levels support cumulus development in that area. 52

53 Mountain Wave 1) Rotor located beneath wave crests generally at or near the height of the disturbing terrain tops. Detrimental in two ways: 1) Turbulent flow (by definition!), and 2) Wind flow reversal possibilities as rotor can oscillate or move up and down in the atmosphere. If the rotor contacts the ground the flow switches to southeast rather than a prevailing direction of northwest as depicted in the example diagram. 2) Mountain wave is a laminar flow above rotor level. It is smooth ... turbulence in a wave is that associated with the rotor zones! 3) Note that wave crests slope upwind with altitude ... but the first wave is downwind of the wind flow disturbing range. Lift is NOT linked to a wave on the upwind side of the mountain slopes. If lift is in this area, it is slope/ridge lift! 4) Lenticular clouds are in the smooth air and form because of lifting, cooling, and condensing due to moisture availability. Cloud moisture evaporates by the downwind edge as air is descending from the wave crest and heats due to pressure increases. 5) Lift is found as air ascends ahead of the wave crest. Climbout on tow is accomplished by utilizing the lift on the leading edge of the rotor or (if you are lucky) in lift areas ahead of the rotor in smoother air. Thermals can sometimes be supported due to the upward lifting on the upwind side of the rotor, depending upon thermal structure of the lower atmosphere. 6) Note the depicted temperature profile of a mountain wave. A temperature inversion needs to be present near the ridge top height. The lapse temperature conditions below and above the stable layer (inversion layer) allow the wave to propogate vertically. That is why the wave can go to great heights (>50,000 feet MSL) even though the mountains are only 10,000 feet high! The stable layer allow the wave to form and propogate downstream (if there are no further disturbing boundaries that cancel or augment the wave). (Notes Continue) 53

54 Mountain Wave Visible Satellite Image for 615 PM PDT 6/15/99 (0115Z 6/16/99) Mountain wave denoted on the lee of the Sierra Nevada from the Minden area at least as far south as Inyokern. Due to the late afternoon sun angle, the cloud-free Southern Sierra crest is visible but the lifting action of the primary mountain wave at the lee visibly marks the wave with lenticular clouds. Wave Notes (continued): 7) Aeromedical aspects: Wave generally forms with strong winds that occur during our cool season months when the jetstream is at lower latitudes. Therefore it can be -20 deg C or colder at altitudes of 18,000 feet or less! Dress warm! Oxygen use is a given as waves have the potential to take you to high altitudes. 8) Risk factors include, but not limited to, turbulence in rotor; cloud cover filling below while flying in wave (undercast!); Flutter problems as you begin to fly in regions where you have high True Air Speeds vs. Indicated Air Speed, e.g., Glider at 80 Knots penetrating upwind from one wave to another at 20,000 feet actually flying at 112 Knots TAS!!!; Watch speed-to-fly when you are in sink as you have to fly FAST to get from one wave lift zone to the next !!!; Lastly, watch cloud clearances. You are likely to be flying in a regime where jet traffic could pop out of clouds at 450 knots plus. If above 10,000 feet you need to remember there is a reason for that 1-mile horizontal cloud clearance!! 54

55 Mountain Wave Wave Presence for Long Distance Flight Example: 6/15/99
Late Spring Mountain Wave Development; Wednesday, June 15, 1999 As a short-wave trough (upper air disturbance) swings through the general trough position along the California Coast, the wind flow aloft increases slightly over the Southern Sierra Nevada with consistent light-to-moderate south-southwest wind at the ridge tops (15-25 knots). In keeping with guidelines written up by Meteorologist Doug Armstrong in Carl Herold’s book, Glider Crewing and Landing Sites in the Deserts of California and Nevada, a mountain wave did develop during the afternoon hours of the 15th. Similar situations occur more frequently than many might suspect with Sierra Nevada wave conditions having been observed into July (altitudes to 27,000 feet MSL). [Presenter’s Comments: Note the variety of weather that can occur in short period of time in the last three examples presented: June 13th gave us the Mono Lake Shear Line; June 14th the Flying “M” Shear Line; and the 15th a full Sierra Mountain Wave!] Again, see the Appendix for a summary of meteorological notes by Doug excerpted from Carl’s book. 55

56 Moisture Surges Southwest U.S. Monsoon
Warm Season Sources Southwest U.S. Monsoon Low level and/or mid-level Significantly deep trough developing moisture field due to the dynamics But a southwest flow is generally a very dry flow East Pacific hurricane activity Mid/High Clouds with a major hurricane release of its accompanying moisture Moisture Surges Generally for the Great Basin, a southwest wind flow aloft is a drying flow and provides essentially “blue” conditions. Advection or movement of moisture into the Great Basin can occur from different directions with each affecting soaring conditions. The establishment of a southeast wind flow aloft with bring sub-tropical monsoon moisture into the area. Often the initial stages simply raise humidity levels around the 12,000 to 16,000 foot elevation and provide cumulus markers for distance flying. Sometimes mid-level, non-convective cloudiness and/or cirrus is moved into the area that suppresses thermal development due to cloud shadowing. Yet other times the moisture surge will be at the lowest levels noted by a rise in surface dew points at observing stations along the Colorado River and into the Southern Great Basin. This, too, will result in cumulus development in the thermal process. Another source of moisture (and cloudiness) will be a stronger, developing trough or low pressure center with its associated dynamics and upward air movement. Any low capable of producing its own moisture field by good vertical motion is likely to inhibit long-distance flying because of cloud shadowing as well as thermal shearing with increased wind. One other source of moisture sufficient to provide cloudiness or increased water vapor is the East Pacific hurricane. Weaker hurricanes, tropical storms, or depressions may send only increased water vapor and few mid-level clouds north toward the Great Basin resulting in cumulus markers for soaring. Either too strong thermal conditions with this increased water vapor will often result in widespread thunderstorms, or stronger hurricanes will send so much moisture in the form of mid- and high-level cloudiness that thermals are suppressed due to cloud shadowing. Satellite imaging is the best tool for monitoring the progress of moisture surges toward the Great Basin ... minor surges best monitored by the water vapor images. Widespread cloudiness will be depicted best on the visible and infrared imaging.

57 East vs. West Great Basin
Time of Year Sub-Tropical Moisture Progression Parawon UT (Late June/Early July) East NV (Mid-Late July) West NV (Late July/Early August) Slower Thermal Processes Dry west; Slower start per moisture-deficit More attenuation; CA and local “Haze” West NV, slightly lower terrain West Great Basin Enhancements Shear line influences prevalent within 50 s.m. of the Sierra Nevada Front East vs. West Great Basin Time of Year Sub-Tropical Moisture Progression -Parawon UT (Late June/Early July) -East NV (Mid-Late July) -West NV (Late July/Early August) Sub-tropical moisture can begin to influence the 4-corner states of New Mexico, Arizona, Colorado, and Utah as early as late June. As the warm season or summer progresses, its influence spreads westward with occasional northward thrusts, depending on other synoptic pattern changes. However, Eastern Nevada is often over-developed because of the proximity to wind flow advecting sub-tropical moisture versus that of Western Nevada. Slower Thermal Processes -Dry west; Slower start per moisture-deficit Less moisture contribution to the instability or lifting process with the West Great Basin generally being drier. -More attenuation; CA and local “Haze” As mentioned, atmospheric attenuation due to man’s influences is now more prevalent in the West Great Basin including the Southern California Deserts than even a decade ago. This attenuation delays convection time with its influence. -West NV (Central and East NV with higher terrain) The valley portions of the East Great Basin tend to be slightly higher than the West and therefore provide slightly better thermal conditions on that account. Enhancement in West Great Basin -Shear line influences prevalent within 50 statute miles of the Sierra Nevada Front. While there is shear line presence in all of the Great Basin, they appear to be greater in number and variability close to the Sierra Nevada and Tehachapi Mountains. 57

58 Soaring = f(Moisture Changes)
Hypothesis: Annual Climate Changes Impact Soaring Moisture Contribution Dew Points rise to the southeast over the Great Basin La Nina/El Nino Influences La Nina Dry south; Thunderstorms develop less frequently El Nino Moist ground delays (thermal) soaring season Upon initiation, more thunderstorm activity Other Climatic Oscillations’ Impact? Arctic Oscillation, Pacific Decadal, Madden-Julian Oscillation Soaring as a function of Moisture Changes Hypothesis: Annual Climate Changes Impact Soaring I state that the recently advertised meteorological phenomenon such as El Nino, La Nina, etc., are providing changes from Great Basin soaring norms. This is hypothesis is obvious and meteorologically sound. What is more difficult is projecting how the changes influence the summer soaring season in the Great Basin. Moisture Contribution -Dew Points rise to southeast across the Great Basin as flow patterns change that favor southerly flow more often. La Nina/El Nino Influences -La Nina There is a climatic tendency for it to be drier to the south under a La Nina condition. Therefore thunderstorms tend to develop less often and thus less over-development in shutting down thermal production. -El Nino With El Nino situations there is more surface moisture with above normal rainfall. Therefore the moist ground delays (thermal) the soaring season. With the additional East Pacific Hurricane activity under an El Nino, there is also more thunderstorm development during the warm season. -Other Climatic Oscillations’ Impact? There are several other types of atmospheric oscillations under study, e.g., Arctic Oscillation, Pacific Decadal, and the Madden-Julian Oscillation. The impact and timing of these oscillations, while quite observable, are yet under study for their climatological influences in the Western United States (and subsequently their impact on soaring meteorology!) 58

59 Infrared Satellite Imagery
Cloud top temperature Good delineator for high clouds Infrared Satellite Imagery Infrared satellite imagery is very useful for determining the altitude of the highest clouds by comparing the cloud top temperatures as measured by satellite with the area upper air temperature soundings. The area coverage of mid and high level cloudiness is well delineated by such imagery. Low level cloudiness can be hard to detect on such imagery as the cloud temperatures can be very close to that of the earth.

60 Water Vapor Satellite Imagery
Moist and dry air boundaries Active convection often along interface Determine Raob representativeness of task area? Water Vapor Satellite Imagery Water vapor satellite imagery shows the overall extent of water vapor (not visible moisture). The demarcation between dry and more moist air masses is very pronounced. Often this discontinuity of moisture fields will act as a focus for thunderstorm development...or well-defined cumulus. Also, some clue to the upper air sounding’s area representativeness of moisture can be determined by this type of satellite imagery. As you look at this image note that the black-to-dark or brownish areas show an atmosphere that is very dry. White areas are more moist with perhaps some cloudiness. Green areas,under the depicted color scheme (shown along the bottom of the image), are areas of cloudiness. In task-planning, fly into the area of the more moist (water vapor) air early in the day to take advantage of early cumulus development, but plan to be out of such an area and toward drier areaas before any thunderstorm over-development can occur.

61 3. Synoptic-Scale Weather Patterns
Weather Types Favorable to Long Distance Soaring Type #1: Four-Corner High Type #2: Strong Ridge Type #3: Low Center, Trough, Short-wave Proximity Type #4: Building Ridge Aloft 3. Synoptic-Scale Weather Pattern Recognition Weather Types Favorable to Long Distance Soaring Based on reports from tasks pilots have flown and what I have studied, I have currently classified four types of synoptic-scale weather patterns that seem to support or be favorable for long distance flying in the Great Basin. In conjunction with discussions with Carl Herold and his input, consider what follows as examples of these weather types with a variant on Type #3. More examples of these weather pattern types can be found courtesy of the Pacific Area Soaring Council (PASCO) and Carl Herold in their “Cross-Country Soaring Seminars” in 1999 and These weather types are numbered and classified by the following weather features: Type #1: Four-corner high; Type #2: Strong ridge; Type #3: Low center, trough, or short wave proximity; and, Type #4: Building ridge aloft.

62 Type #1: The Four-Corner High
High pressure centered aloft near the Four Corner area of the Southwest U.S. Most recognized, "Classic" long flight pattern Good low level heating de-stabilizes the air mass Light surface wind Lower layer warm air advection Monsoon moisture tap ... therefore usually not a long-lived pattern Good soaring ... but days get truncated with afternoon TSTMs... often widespread Map Type #1: The Four-Corner High When long flights are recalled in the Great Basin area, the “classic” weather pattern that comes to mind is that of the four-corner high pressure situation ... and for good reason. When occurring, this pattern produces consistently good soaring over the area. Good low-level heating develops over the Great Basin from generally light wind allowing good surface heating in bright sun and warm air advection at the lower levels in a southerly wind flow. Often the pressure over the Great Basin is higher than that of interior California and surface afternoon westerly winds in the western Basin valleys are suppressed so minimal afternoon washout occurs. The initial advances of increased water vapor provide cumulus markers without thunderstorm over-development. The axis of the ridge east of the area and lower pressure aloft lifts any inversion “capping” to relatively high altitudes (often in excess of 16,000 feet MSL). Unfortunately a wind flow from the southeast in July and August provides only about 24 to 48 hours before too much moisture arrives and widespread thunderstorms develop. Therefore one must be ready to fly the first day of this pattern because it is unusual for the pattern to last more than two days, and quite often only provide one day before afternoon thunderstorm activity prematurely truncates soaring days.

63 Type #1: 6/18/88 ASI to Keeler and return Map Type #1: June 18, 1988
A long flight was made down to Keeler from Air Sailing under the classic scenario. The delta-P from Reno to Sacramento was 2.8 mb but Tonopah to Fresno was 5.3 Mb. Not only was high pressure in place near New Mexico but a weak trough of low pressure was passing aloft through Washington and Oregon de-stabilizing areas well to the north. With the axis of the ridge to the east and lower pressure just off the Baja California coast, the subsidence inversions were not strong nor even readily apparent in referring to the soundings for Winnemucca and Las Vegas. With maximum temperatures climbing to the lower 90s F. in the northern Great Basin, thermals shot up to 18,000 feet MSL plus before encountering a cap. Notice the moisture presence around Las Vegas as depicted by the Desert Rock sounding. The morning millibar delta-T at Winnemucca was around 30.

64 6/18/88 Raobs WMC 94/50 RNO 90/58 TPH 83/52 LAS 98/78 6/18/88 Raobs

65 Type #2: Strong Ridge Light wind Low level heating
Thermal trough well to the west of task area Impulse aloft over ridge axis; or, Ridge axis aloft east of the task area Map Type #2: Strong Ridge This pattern is associated with surface temperatures that are much above normal but the ridge axis is offset to the east and therefore not “capping” thermals by the subsidence inversion. Light wind, bright sun, high maximum surface temperatures, and normal to slightly above normal diurnal temperature variations are noted. The thermal trough is well to the west of the task area to allow for minimal afternoon Zephyr washout. Again, this weather type is well recognized as one providing excellent soaring conditions.

66 Type #2: 8/9/96 Long-lived, extraordinary pattern
Numerous 1000Km flights Over a 4-day period Map Type #2: August 9, 1996 August 9th was in the middle of one of the best soaring periods this forecaster has ever seen. Over the period beginning Wednesday, August 7th, and going through Sunday, August 11th, there were at least kilometer flights accomplished from Minden, Truckee, Tehachapi, and the Flying ‘M’. The lift conditions were so good that in a couple of those flights the task was flown without benefit of water. The day of August 9th was singled out as the example because a number of 1000-kilometer flights were flown on that day (including Hannes Linke who didn’t have a working barograph and Peter Ryder who did it without water from the Flying ‘M’!). It was also the 2nd day that Rob Morgan flew the task from Tehachapi because his barograph didn’t work when he flew it on the 8th! It is highly unusual for such outstanding conditions to persist more than a couple of days without leading to either over-development or a change in the pattern to less ideal conditions. Note that high pressure was west of Nevada but a weak impulse was crossing the ridge axis off the Washington/Oregon coast that lifted the subsidence cap. The surface delta-P from Reno to California was 5.3 millibars so the thermal trough was well entrenched through interior California and the afternoon Zephyr was eliminated.

67 8/9/96 WMC 98/48 RNO 95/53 TPH 95/61 LAS 99/80 Daytime maximum temperatures for the western Great Basin were in an upward trend throughout the period, e.g. on the 7th, Reno’s high was 84 degrees F., jumping to 92F on the 8th, 95F on the 9th, 98F on the 10th, and then 99F on the 11th. Moisture influx was not occurring rapidly with only winds of 5 knots or less from the surface throughout the convection layer. Thermals were generated early in the day and quickly rose up to the strong subsidence cap at 18,000 feet MSL. There was just sufficient moisture to allow high-based cumulus but not enough to support thunderstorms. The delta-T from 850 to 500 millibar showed values in the lower to mid 30s. High/low temperatures around the Basin: Winnemucca 98/48, Reno 98/53, Tonopah 95/61, and Las Vegas 99/80.

68 Type #3: Low Center, Trough, or Short Wave Proximity
Ridge axis to the east; Trough axis proximity De-stabilizing by cold air advection aloft But light wind and/or split in the jet aloft Thermal trough closer to NV; but... Low level Zephyr washout delayed Still able to heat lower levels Prevalent pattern for long distance soaring! Map Type #3: Low Center, Trough, or Short Wave Proximity This weather pattern seemed to be the most prevalent, even if not the best, in providing soaring conditions for long distance flying. Low pressure, in the form of a weak trough or a closed low pressure center, and the ridge axis east of the area, provides for an de-stabilized atmosphere over the Great Basin. If the wind flow aloft is weak, thereby not shearing thermals, and sunny conditions prevail for good surface heating, cooler air accompanying the trough aloft contributes to large vertical totals (850- to 500-millibar temperature lapse rate) and de-stabilizes the atmosphere with little accompanying subsidence inversion. It often takes a split in the wind flow aloft to provide light wind with a trough in the vicinity of the Great Basin. Often the surface thermal trough is closer to Nevada but that only affects the western Basin valleys in the afternoons and not necessarily adversely affects lift and altitude along the higher terrain of the state. A bigger positive factor is the thermal consistency and altitude providing terrain clearance.

69 Type #3: 7/7/88 Flight of 350 miles Map Type #3: July 7, 1988
Following a weak surface frontal passage through the Pacific Northwest, a weak southwest wind flow persisted over Nevada with a slowly filling trough aloft. High pressure had built over the Pacific Northwest at the surface and provided a delta-P from Reno to Interior California of 3.2 to 4.1 millibars. Sunny conditions prevailed and there was a warming trend underway for the area. A flight of 350 miles was undertaken on what appears to have been a “weak” thermal day, but thermals remained consistent and undoubtedly elevated heat source thermals played a role in providing enough time to fly the task. It appears that 14,000 feet MSL was the likely maximum altitude used for this flight and undoubtedly the start time was not until the afternoon hours.

70 7/7/88 Raobs <WMC 84/54 <RNO 84/49 <TPH 90/56 <LAS 103/77

71 Type #3(a): Proximity of Low Pressure Center
<Low off Southern California coast provides cooler air aloft upstream to de-stabilize <Elevated heat source influence contributions Map Type #3(a): Proximity of Low Pressure Center This is considered a sub-type or variant of the “Trough” pattern. Cooler air aloft associated with low pressure centers is one of the key components in de-stabilizing an air mass and supporting long distance soaring flight. While high pressure may be located over Nevada, the proximity of a low upstream, with its cooler air aloft, provides good soaring conditions as long as that low is weak enough to not support strong vertical motion and resulting cloudiness.

72 Type #3(a): 6/19/93 1000Km flights from Truckee And Minden area
Map Type #3(a): June 19, 1993 Despite higher pressure just east of the area, low pressure off the Southern California coast de-stabilized the atmosphere aloft for the Southern Sierra Nevada in combination with near normal afternoon surface high temperatures. The surface delta-P between Reno and Interior California was 4.3 millibars thereby suppressing afternoon Zephyr development. Again, mountain top heat sources provided much better altitudes than Basin valley locations. There were several 1000-kilometer flights from the Minden and Truckee area with this pattern.

73 6/19/93 Raobs <WMC 86/47 <RNO 88/57 <TPH 86/54 <LAS 94/72

74 Type #4: Building Ridge Aloft
2 Examples / Next 4 Slides <Temperature trend upward Surface temps climbing faster than aloft Subsidence not strong Large diurnal temperature spread in transition <Light wind aloft Height gradient small <Suppression of westerly washout Map Type #4: Building Ridge Aloft After a trough passage and pressures aloft begin to rise, strong subsidence may or may not develop. Surface temperatures starting below normal will begin a recovery and there are cases that show long distance soaring occurs during this temperature recovery period. What is required is enough strong energy to raise surface temperatures faster than temperatures aloft. This is usually accomplished by light wind and suppression of the Zephyr. It is during these periods that above normal diurnal temperature variations often occur.

75 Type #4: 6/13/88 500 Mile Flight Map Type #4: June 13, 1988
Following a weak trough passage through Western Nevada, pressure aloft began to rise. Note the residual cool air at the surface in the Truckee Meadows as Reno reported a low temperature of 27 degrees F. ... but recovered to a high temperature for the day of 81F. Thermals reached sufficient altitude and strength to support a 500-mile soaring flight. The delta-P of 3.5 millibars from Reno to Interior California undoubtedly helped the temperature recovery with light wind at the surface as well as aloft.

76 6/13/88 Raobs <WMC 81/42 <RNO 81/27 (!!!) <TPH 78/M
<LAS 95/70 6/13/88 Raobs Note: Look at the extreme diurnal variation in the Reno minimum and maximum temperature on this date.

77 Map Types also varied as season passed!
This chart represents a breakdown of various map types associated with soaring reports received over the warm season (summer) of 2000. Type # Corner Classic Type #2 17 Strong Ridge Type #3 23 Low Pressure Trof Type #4 5 Building Ridge Their does appear to be a Prevalence for a favored synoptic pattern by the time of year, I.e., -May/June Type #3 -July Type #1 -August/Sept Type #2 Map Types also varied as season passed! 77

78 4. Weather Forecasting Forecast Funnel Soaring Indices
Automated Soaring Forecasts Dr. Jack and BLIPMAP Other Automated Forecasts NWS IFPS (Gridded Data) 4. Forecasting Background In reviewing the climate, the Great Basin has been determined to provide consistent long-distant flights. Data for individual starting sites must be reviewed by the pilot so that favorable conditions are known and recognized. As previously discussed, factors such as higher than normal diurnal temperature variation are good indicators that the soaring is above average (in conjunction with synoptic patterns). Most long distant flights fail to utilize the earliest part of the day. In doing so up to 50 miles of distance may be lost in not recognizing the conditions that would allow flight as early as possible. Local expertise is invaluable in this area and consultation with experienced Great Basin pilots will avoid this pitfall. The Forecast Funnel involves using weather data in working toward a given flight day, in order: -Site Climate Knowledge; -Outlook Forecasts (8-10 Day Time Period); -Extended and Zone Forecasts (2-7 Day); -Persistence; and, -Flight Day.

79 A Glider Pilot’s Forecast Funnel
A Process of Soaring Forecast Refinement Site Climate Outlook Forecasts Extended and Zone Forecasts (2-7 Day) Persistence Flight Day The Glider Pilots’s Forecast Funnel … Empowering the Soaring Pilot to Forecast In reviewing the climate, the Inter-mountain West has been determined to provide consistent long-distant flights. Data for individual starting sites must be reviewed by the pilot so that favorable conditions are known and recognized. As previously discussed, factors such as higher than normal diurnal temperature variation are good indicators that the soaring is above average (in conjunction with synoptic patterns). Most long distant flights fail to utilize the earliest part of the day. In doing so up to 50 miles of distance may be lost in not recognizing the conditions that would allow flight as early as possible. Local expertise is invaluable in this area and consultation with experienced Great Basin pilots will avoid this pitfall. The Forecast Funnel involves using weather data in working toward a given flight day, in order: -Site Climate Knowledge; -Outlook Forecasts (8-10 Day Time Period); -Extended and Zone Forecasts (2-7 Day); -Persistence; and, -Flight Day weather parameters as previously discussed.

80 Soaring Indices(#1) Thermal Index Lift = f()T) Great Basin
(Thermal) Soaring Indices (#1) The Thermal Index (TI) is well-defined in soaring texts. Its application in the Great Basin is only significant to the extent that it confirms that a parcel remains buoyant through whatever level is selected as a reference (whether that level is 10,000 feet or 15,000 feet MSL). Rather it is more important in the Great Basin to additionally account for the maximum altitude of the thermals as an indicator of thermal strength. Courtesy of NWS Forecasters Doug Armstrong and Chris Hill in 1975, an empirical equation for maximum lift, the Soaring Index (SI) was developed that stressed the importance of both delta-T, like the TI, and the maximum thermal altitude. The reasoning behind incorporating the maximum altitude for the determination of maximum lift is that given enough altitude, some acceleration of the rising parcel through the convective layer occurs and thus provides better lift than the TI might indicate based on reference level delta-T alone. The Soaring Index also has weaknesses in that it can not account for the influences of humidity, which can add as much as 30-50% to the buoyancy of a rising thermal into drier air. The density difference of a surface parcel increases as it encounters drier air aloft so thermals get stronger with altitude. Therefore, relative humidity “boundaries” are also important as thermal enhancer or detractors. Additionally, thermals have tremendous mass such that they may “punch” through layers without being moved to a large extent by the layer mean wind.

81 Soaring Indices (#2) Soaring Index
Great Basin Soaring Index Lift = f(Convection Altitude and )T) Soaring Indices (#2) John Joss’ book, SoarSierra, provides the actual equation for the Soaring Index (which might be better named the Great Basin Soaring Index to avoid confusion with the term being loosely applied all across the country for various other soaring forecast algorithms). Defining the following: LNEC...Temperature (degs C) at 4000' AGL from the morning sounding; LXEC...Temperature (degs C) at altitude of the dry adiabat of the afternoon maximum surface temperature intersecting the morning temperature sounding; ALTx….Altitude (feet MSL) that the dry adiabat from the forecasted surface maximum temperature intersects the morning sounding; Then the Soaring Index is the expected lift at the time of the maximum temperature expressed in Feet Per Minute (FPM); SOARING INDEX = {[(LNEC-LXEC) x 10] + ALTx/100}3 The Great Basin Soaring Index is used by NWS Reno in their computations for maximum lift on their soaring forecast product.

82 Vertical Totals [)T(deg C) 850 mb to 500 mb]
Soaring Indices (#3) Great Basin Vertical Totals [)T(deg C) 850 mb to 500 mb] Upper 20s average to good 30 to 34 very good 35+ excellent (too unstable many times) Soaring Indices (#3) Another good index for thermal activity is that of the temperature lapse rate (in degrees C.) between the 850-millibar and the 500-millibar level (a vertical delta-T, or vertical total). Delta-T values in the upper 20s are about “average” to “good” for thermals. Usually higher thermal altitudes are going to eventually be reached when the lower 30s are seen, and especially so by the mid 30s. An effective “limit” is 42 degrees C. for the vertical total of the dry adiabatic lapse rate between 850- and 500-millibar levels. Vertical totals reaching the mid 30s or higher tend to reflect an atmosphere getting unstable and will favor widespread thunderstorm development, especially with any increase in moisture.

83 Instability Indices(#1)
Great Basin K-Index Uses Vertical Totals and 2 fixed reference levels )T(C) dew point(C) dew point depression(C) 5+ = some cumulus possibilities Thunderstorms increase in the range Instability Indices (#1) The K-Index is an indicator of thunderstorm activity. The Great Basin, with its tremendous capabilities to support dry thermal development, necessitate a different set of “K” values than presented in many meteorological texts, the FAA’s Advisory Circular AC-006, Aviation Weather, included. The K-Value is defined as: delta-T(C) dew point(C) dew point depression(C) Lower K-values generate thunderstorms for the Great Basin. The presence of any mid-level moisture represented by reduced 700-millibar dew point depressions or low-level moisture indicated by the 850-millibar dew point generally result in some cumulus (a loose threshold K-value of 5 seems to indicate cumulus possibilities, and a thunderstorm at a couple of the “favored” locations). A combination of higher than normal low-level dew points and mid-level moisture (a K-value of or more) indicates thunderstorms in many if not all of the “favored” locations. But these K-thresholds vary extremely. The synoptic weather pattern and the overall moisture in the air mass can detract from or increase the threat of thunderstorms for the same K-value from situation to situation. By the time the K-value reaches the upper 20s, however, over-development from thunderstorms around the sounding site consistently reaches the likely category.

84 Instability Indices (#2)
Great Basin Lifted Index (LI) and Showalter Index (SI) Lower layer moisture influences on the convection process / thunderstorm indicator > 10 stable (weak convection) < -4 too unstable (severe weather) Instability Indices (#2) The Lifted Index (LI) and Showalter Index (SI) reflect the delta-T (like the Thermal Index) at 500-millibar after taking into consideration lower level moisture parameters. Meteorology texts indicate LI and SI values greater than 10 represent generally too stable an atmosphere for thunderstorm development...and values less than -4 almost always indicate severe thunderstorm development. These threshold values seem to apply to the Great Basin reasonably well with ideal values for thermal development in parenthesis: Showalter (+7>+3) This index uses temperature and dew point at the 850 mb level raised as a parcel dry adiabatically until saturation; and then moist adiabatically to the 500 mb level( 18,000 ft MSL). The difference in temperature between the lifted parcel in degrees C from the 500 mb ambient temperature becomes the value of the index. Normal ranges are linear from +20 to -10 with plus values more stable and the thunderstorm threshold around +4 (degrees C.) Lifted Index (+5>0) This index is similar to the Showalter except that the initial temperature and dew point in the lifting process start at 100 mb above the surface (to minimize surface temperature and humidity effects.) The thunderstorm threshold is around 0.

85 Thermal Lift Indices Work
Thermal Index (Williams/Higgins) Maximum Lift (Lindsay/Lacy) Soaring Support (Aldrich/Marsh) Soaring Index (Armstrong-Hill) Soaring Lift Indices Work . Thermal Index (Williams/Higgins) Williams 1955 / Higgins published Thermal Index 1963 . Maximum Lift (Charles Lindsay and Stan Lacy) Regression equations based on Frederick MD Flights Forecaster’s Handbook #3; Soaring Meteorology for Forecasters (9/72) . Soaring Support Individual Contributions to Soaring John Aldrich (Weather Bureau, Los Angeles) and John Marsh (Weather Bureau, Reno) late 60s/early 70s Soaring Index (NWS Forecasters Doug Armstrong and Chris Hill; NWS Reno mid-1970s) (Diagram courtesy of John Joss in SoarSierra) 85

86 Wave Strength Forecasting
Wave Nomogram (Herold/Armstrong) Wave Strength Forecasting Wave Nomogram - March 1986 (Carl Herold/Doug Armstrong) Use of Change-In-Pressure along with observed Maximum Wind Speed between 10K-20K feet. 86

87 Traditional Soaring Forecasts
Persistence Nowcasting Soundings Satellite Analysis Algorithm Use Traditional Soaring Forecasts Persistence Nowcasting Soundings Satellite Analysis Algorithm Use 87

88 Thermal Index Prediction (TIP) Dr. John W. (Jack) Glendening
Estimate for the Current Day Thermal Soaring Potential Two Day Thermal Soaring Outlook Several Sites Mountain Top Experiment (Walker Ridge) Thermal Index Prediction (TIP) Dr. John W. (Jack) Glendening -Estimate for the Current Day Thermal Soaring Potential -Two Day Thermal Soaring Outlook -Several Sites: Avenal, Hollister; Minden; Williams; Mt.Williams; Crazy Creek; State College, PA; Arlington, WA. -Mountain Top Experiment for Walker Ridge (Adjusts for the difference between smoothed model terrain and actual ridge elevation.) URL: (TIP Forecasts) URL: (Experimental TIP Forecast for Walker Ridge) URL: (Thermal Index Definitions and Theory Page) URL: URL: 88

89 Boundary Layer Information Predictor Maps(BLIPMAP)
Thermal Soaring Parameters (over a geographic region) -Numerical Model Outputs General Air Mass Lift Boundary Layer Information Predictor Maps (BLIPMAP) (Dr. John W. (Jack) Glendening) . Thermal soaring parameters over a geographic region . Numerical model post-processing Thermal Updraft Velocity (W*); Height of Critical Updraft Strength (Hcrit); Boundary Layer Top; Thermal Height Variability; Buoyancy/Shear Ratio (B/S); Wind Speed, Wind Direction, Convergence in Boundary Layer; Maximum Boundary Layer Relative Humidity; Over-development Potential; Boundary Layer Condensation Level (LCL); Convective Available Potential Energy (CAPE); Boundary Layer Depth; and, Surface Heating. General air mass lift; NOT small-scale terrain enhancement; Use relative differences as indicators Output can be single charts or automated over time for a given day URL: Single Time or Sequence URL: 89

90 Wind Information Predictions (WINDIP)
(Simple Mountain Wave Prediction) “Alert” WINDIP List Assumptions Longer Forecast Time Predictions URL: Wind Information Predictions (WINDIP) (Dr. John W. (Jack) Glendening) -Simple Mountain Wave Prediction Components of: Wind speed (Kts), Wind direction, Wind component normal to ridge axis. Available and displayed in a table predicting mountain wave components for several types of numerical models. -Assumptions -Forecast from “Armstrong” Criteria only, I.e.: 700 mb Wind >= 25Kts; 300 mb Wind >= 65Kts; and, Use only within 45-degrees of normal from the ridgeline. -Empirical criteria used to predict mountain wave occurrence are necessarily simplistic and omit several factors which affect wave formation, particularly atmospheric stability. -Longer Forecast Time Predictions (but accuracy beyond 5 days especially inconsistent due to numerical model divergence) -Predictions are for the same forecast period and provided for several models (to indicate forecast variability at a given time). In fact, similar model solutions for a given time period provide some degree of confidence to the numerical solutions provided by WINDIP. 90

91 Linear Wave Interpretation Page (LWIP)
Description Interpretation Notes Links Linear Wave Interpretation Page (LWIP) (Dr. John W. “Jack” Glendening) Description -Mountain wave updraft strength (vertical velocity) is predicted at 1 km intervals from a large-scale forecast of wind and temperature structure. Specifically for locations around Lake Tahoe/Reno (Sacramento Grid) and the Owens Valley (Lemoore Grid). -Displayed as plan views at two different heights and as a cross-section (altitude in km; multiply by 3 for ~1000s of feet) Interpretation -Linear model may produce stronger and more extensive waves than actually occur. -Again, look for “relative predictions” and trends rather than absolute forecasts. -Mountain wave predictions depend upon a large-scale sounding forecast of wind and temperature which differs for each grid. -Boundary layer (thermal layer) is not considered, so waves can be incorrectly forecast to extend down to the surface. Notes: -Atmospheric Sounding predicted by large-scale model of Dr. Ronald B. Smith of Yale University and in collaboration with Dr. James D. Doyle of Navy Research Laboratory at Monterey -Linear theory doe not represent conditions when the airflow around the mountain -Depends on large-scale flow, so “local” mountain waves will differ from those predicted when local wind is different than model. -Since model only allows 3 separate atmospheric layers, predicted waves will be less complex than actually observed Links: URL: URL: 91

92 Automated Thermal Soaring Forecasts
Walt Rogers (WX), MIC CWSU ZLA Two Parts: 1.Pure Model Output (top portion) 2.NWS Forecast Temps as base (lower portion) Limitations NWS Websites Automated Thermal Soaring Forecasts Through the use of numerical model forecasts for the boundary layer meteorology (lower 1 Kilometer of the atmosphere), soaring parameters are being gathered by a program written by Walt Rogers, NWS Meteorologist In Charge working in the FAA’s Los Angeles Air Route Traffic Control Center. This program was in the implementation and testing phase through the summer of 2001 and has been implemented as of January An example product output is being depicted in this slide for the California City soaring area in the Mojave Desert. The program is designed for those NWS Offices who have soaring areas that would provide the FAA with a briefing tool for the soaring community. Along with this automated program, an educational explanation of soaring meteorology terms and equations provide a training tool for all levels of soaring pilots. The implementation and subsequent program output for various Southern and Central California soaring sites leads me to call for input of maximum altitudes and lift rates (in thermal soaring) for an accuracy evaluation of the model forecast output. Input can be made to me, Dan Gudgel at: and/or Walt Rogers at: A brief explanation of the output: -Conditions are presented for three time periods during the day (10 AM, 1 PM, and 4 PM PST); -Top of the Lift is presented (MSL); -Lift rates and Soaring Index at the specified time; -Other indices (K-Index, Lifted Index, and the Lifted Condensation Level); and, -Trigger temperature is also presented for the specified site and other nearby locations. Two Parts: 1.Pure Model Output (top portion) The top potion of the forecast is based upon the (current) 20-km grid of the Meso-scale Analysis Prediction System (MAPS). The soaring parameters forecast and displayed in the top portion are pure model output for three different time periods during the forecast day. 2.NWS Forecast Temps as base (lower portion) This portion provides a man-machine mix whereby the surface temperatures forecast by the NWS at given locations are paired with the closest MAPS Model grid point sounding. Limitations: 1.The model terrain at 20-km grid spacing depicts California terrain poorly. 2.Winds are not currently placed as output parameters but that is planned. 3.Virtual temperature is used for the Model Output surface temperature. 4.Man-machine mix often does not reflect agreement between model forecast and forecaster expectation at the actual soaring site, therefore, soaring parameters are unable to be computed when the surface temperature dry adiabat is not high enough for the model soaring forecasts. NWS Websites at URL: (where ***** is NWS Office Name, I.e., Hanford, Oxnard, etc.) URL: where ***** is NWS Office Name, I.e., Hanford, Oxnard, etc. 92

93 Interactive Forecast Preparation System (IFPS)
“Flagship” Products Not Text -Forecasters Edit Gridded Data Graphical Products -Customer Requested Output Interactive Forecast Preparation System (IFPS) Weather Bureau/National Weather Service products have always been “text.” The IFPS is allowing forecasters to actually edit gridded data sets. The output from that editing is displayed either the traditional text form or displayed in graphical form per the customer requests. The end product is in essence a Man-Machine Mix; and by virtue of the on-going editing process within the NWS Offices, it is more easily updated for use at the time of customer request. Internet Access through the NWS Websites: <> Man-Machine Mix 93

94 Gridded Data Graphical Display of Requested Weather Parameter(s) 94
Examples of terrain sensitive surface and dew point temperature charts as output from the Interactive Forecast Process System and the gridded data set from the NWS Office at Tucson, Arizona. 94

95 5. Miscellaneous Information
Aero-medical Considerations 5. Miscellaneous Information --Aero-medical Considerations

96 Aeromedical Considerations
Soaring good enough that... <Oxygen requirements <Water <Sun protection Aeromedical Considerations Great Basin and West soaring is very good but the conditions giving us that good soaring can be physically harsh to pilots. Remember the high altitude giving us high true air speeds requires oxygen use. Even if you are flying at 11,000 feet MSL for a good portion of the day (hopefully higher), the high temperatures and resulting density are the equivalent of 14,000 feet on a typical Nevada July day. The use of oxygen, lower vapor pressures aloft, and plenty of sun also depletes body moisture at an alarming rate. Bright sunshine over several hours is fatiguing to the eyes and body. In all cases, the first physiological symptom that occurs with any of the above aeromedical conditions is the loss of judgment. Don’t be caught short of wits. Plan to avoid these pitfalls by following a regimen that never lets one of these factors come into being. The best tool you have for completing a long distance flight is your power to analyze ahead of time and adapt to the changing conditions over a long course and time period. Without your judgment you can’t complete the task ... and in a worse case you can hurt yourself!

97 Meteorological Concepts for Soaring in the Western U.S.
Dan Gudgel Meteorologist/Towpilot/CFIG 134 South Olive Street Lemoore, CA (w) ext.223 (h) Meteorological Concepts and Tools for Long Distance Soaring The information compiled from earlier presentations in the Cross-Country Seminars ( ) along with this Brief provides the Soaring Pilot (and aviation in general) an overview of the transition occurring in meteorological services. For any questions, please feel free to inquire and I will attempt to get an answer or reference source for your benefit. Dan Gudgel c/o National Weather Service 900 Foggy Bottom Road Hanford, CA (w) ext.223 (h) Or home

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