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AMS Weather Studies Introduction to Atmospheric Science, 5th Edition

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Presentation on theme: "AMS Weather Studies Introduction to Atmospheric Science, 5th Edition"— Presentation transcript:

1 AMS Weather Studies Introduction to Atmospheric Science, 5th Edition
Chapter 13 Weather Analysis and Forecasting © AMS

2 Driving Question What is the process involved in making a scientific forecast of the weather? This chapter covers: How forecasts are made Limits of forecast accuracy Making your own weather forecasts © AMS

3 Case-in-Point Evolution of Tornado Forecasting
1884: started by John P. Finley, U.S. Army Signal Corps 950 “tornado reporters” were gathering data with criteria Finley established 1886: program discontinued Word “tornado” disallowed in Signal Corps forecasts for fear of public panic s: Air Force meteorologists Fawbush and Miller developed method for forecasting tornadoes Tornado struck Tinker Air Force Base in Oklahoma City, OK on 20 March 1948; motivated Fawbush and Miller List of six atmospheric conditions that preceded tornado outbreak Those conditions reappeared 5 days later Issued first tornado forecast; accurate, saved lives and aircraft Primarily issued for military installations Eventually, U.S. Weather Bureau adopted/allowed tornado forecasting for public distribution Severe Local Storm Warning Center (now the Storm Prediction Center) established in Norman, OK 1952: ban on “tornado” with issue of first tornado watch © AMS

4 International Cooperation
International Meteorological Organization (IMO) founded in 1878 IMO became the World Meteorological Organization (WMO) Headquartered in Geneva, Switzerland, agency of the United Nations Coordinates the efforts of 189 nations and territories in global weather-monitoring program called World Weather Watch (WWW) Provides meteorological information available internationally Global Observing System Data from 6 geostationary and 3 polar orbiting satellites, 11,000 land stations, 4000 ships at sea, 3000 reconnaissance and commercial aircraft, radar, 1300 radiosonde stations, 1200 drifting and 1300 moored buoys Data transmitted to 3 WMO Centers where maps and charts are created, forecasts prepared Maps/forecasts sent to Regional Specialized Meteorological Centers National Centers for Environmental Prediction (NCEP) responsible for U.S. forecasts © AMS

5 International Cooperation
© AMS Global Observing System

6 International Cooperation
Weather forecasting entails Acquisition of present weather data Graphical depiction of the state of the atmosphere Analysis of data and maps Prediction of the future state of the atmosphere Dissemination of weather information and forecasts to the public © AMS

7 Acquisition of Weather Data
Surface Weather Observations Over 2,000 stations across the U.S. operated by National Weather Service (NWS) personnel Staff of other government agencies, including the Federal Aviation Administration (FAA) Private citizens or businesses Automated stations also located in unmanned locations National Data Buoy Center Data gathered for preparation of weather maps and forecasts, exchange with other nations, and use by aviation Observations taken simultaneously Use Coordinated Universal Time (UTC) © AMS

8 Acquisition of Weather Data
Surface Weather Observations, cont. Automated Surface Observing System (ASOS) Result of 1990s NWS modernization 947 ASOS units in continual operation Reports temperature (ambient/dewpoint), pressure (sea-level, altimeter setting), wind (direction/speed), precipitation accumulation, visibility, obstruction to vision, present weather, sky condition Automated Weather Observation System (AWOS) Similar to ASOS 163 FAA-owned and 1149 non-Federal NWS Cooperative Observer Network Volunteers Provide daily precipitation, and temperature readings © AMS

9 Acquisition of Weather Data
Upper-Air Weather Observations Radiosondes Radio-equipped instrument package Transmits upper air information to a ground station (rawinsonde observation) 92 radiosonde observation stations © AMS

10 Acquisition of Weather Data
10 © AMS Locations of radiosonde observation stations.

11 Weather Data Assimilation, Depiction and Analysis
Weather reported by each observation station is depicted on a map by a station. 11 © AMS

12 Weather Data Assimilation, Depiction and Analysis
Surface weather maps Isobars: Connect points of equal air pressure Isobaric analysis reveals locations of anticyclones and cyclones, troughs and ridges, horizontal pressure gradients Drawn at 4-mb intervals 12 © AMS

13 Weather Data Assimilation, Depiction and Analysis
Surface Weather Maps, cont. Cyclone centers are indicated by the symbol L (low) Closely spaced isobars around cyclone indicate steep pressure gradient and strong winds Fronts originate at storm centers Anticyclone centers are mapped as an H (high) Usually a relatively weak horizontal pressure gradient, shown by widely spaced isobars, resulting in weak or calm winds Synoptic surface maps are drawn every 3 hours for North America, and every 6 hours for the Northern Hemisphere © AMS

14 Weather Data Assimilation, Depiction and Analysis
Upper-Air Weather Maps Plotted on constant- pressure surfaces Height contours labeled in meters above sea level Drawn at 60 m intervals Altitude of pressure surface varies because of mean temperature differences Air pressure drops more rapidly in cold air than in warm, due to density differences Isotherms plotted as dashed lines Drawn at 5 C deg intervals Sample 500-mb analysis (NOAA) © AMS

15 Weather Data Assimilation, Depiction and Analysis
Upper-Air Weather Maps, cont. Cyclonic and anticyclonic curvature shown in contours by troughs and ridges in the prevailing westerlies Center of a ridge is relatively warm with high height contours, labeled with an H. Often linked to a warm-core anticyclone at the surface. Center of a trough relatively cold with low height contours, labeled with an L. Often linked to a cold-core extra-tropical cyclone at the surface. Winds that blow across isotherms produce air advection Cold air advection occurs where winds blow from colder to warmer locations Warm air advection occurs where winds blow from warmer to colder locations 15 © AMS

16 Weather Data Assimilation, Depiction and Analysis
Computerized data management systems Spurred by deluge of real-time weather information AWIPS (Advanced Weather Interactive Processing System) Used by NWS Offices since 2000, AWIPS II began roll-out in 2011 Receives and organizes ASOS data plus analysis and guidance products from NCEP Allows meteorologists to display, process, and overlay images, graphics, and other data 16 © AMS

17 Weather Prediction Hydrometeorological Prediction Center
Short range: 12-, 24-, 36-, and 48-hr forecasts Medium range: 3- to 7-day extended outlooks Climate Prediction Center Long range: 6-10 day, 8-14 day, 30-day (monthly), 90-day (seasonal), and multiseasonal outlook Numerical Weather Forecasting Computers programmed with numerical model of the atmosphere Model of equations relate wind, temperature, pressure, and water vapor concentration Current data used to predict atmospheric properties only a few minutes into the future, that prediction becomes the starting point for another few minutes into the future, that prediction… Repeated until 12-, 24-, 36-, and 48-hr forecasts are achieved 17 © AMS

18 Weather Prediction Numerical Weather Forecasting
Computers programmed with a numerical model of the atmosphere Model of equations that relate wind, temperature, pressure, and water vapor concentration Uses present data to predict values of atmospheric properties for a grid of points on a uniform pressure surface Millions of computations go into 12, 24, 36, and 48-hr forecasts 18 © AMS

19 Weather Prediction North American Mesoscale Model (NAM)
Contains NOAA Environmental Modeling System (NEMS) Divides troposphere into 60 vertical layers Forecasts every 6 hours out to 84 hours Nested Window Run (NWR) Contains images from Weather Research and Forecast Model (WRF) Run 4x a day, forecasts at 3-hr increments to 2 days Rapid Update Cycle (RUC) Features 50 levels with horizontal resolution of 13 km Provides short-range, hourly numerical weather guidance Rapid Refresh (RR) scheduled to replace RUC Global Forecast System (GFS) 64-level model operating at different resolutions and forecast periods Runs 4x a day 19 © AMS

20 Weather Prediction To optimize weather forecasting with numerical models: Ensemble forecasting Numerical model generates several forecasts based on slightly different initial conditions If forecasts are consistent, they are considered reliable Model Comparison Comparison is made among forecasts produced by different models If they agree, the forecast issued with a high level of confidence If forecasts are inconsistent using either technique, forecast is considered unreliable 20 © AMS

21 Weather Prediction Forecasting Tropical Cyclones
U.S. Army Signal Corps initially in charge of observation/ forecasting 1873: gathered reports from Cuba to help detect tropical cyclones 28 September 1874: first plotted hurricane 1890: forecasting moved to civilians (U.S. Weather Bureau) Little attention paid to tropical cyclones 1898: Spanish-American War increased interest in tropical cyclone forecasting Fear hurricane destroying U.S. fleet increased weather stations in the Caribbean Technological advances Invention of radio allowed ship-to-shore reports 1930s: upper air monitored 1950s: weather radar at coastal stations observed tropical storms 1960s: remote sensing via satellites began Recently, buoys have provided additional information Aircraft can now deploy dropwindsondes (similar to a radiosonde) to receive sounding from inside storm 21 © AMS

22 Weather Prediction Forecasting Tropical Cyclones
1940s: Atlantic hurricane forecasting split between Weather Bureau offices in Miami, New Orleans, Washington, DC, Boston, and San Juan 1967: designated Miami office as the National Hurricane Center (NHC) Today, forecasting split between NHC and the Central Pacific Hurricane Center (CPHC) in Honolulu. NHC responsible for issuing statements for tropical cyclones in Atlantic basin and eastern Pacific basin to 140°W Operates SLOSH model for prediction of storm surges CPHC activated when tropical cyclone develops in central Pacific 22 © AMS

23 Weather Prediction Forecasting Tropical Cyclones
Predicting track and intensity Forecasts issued every 6 hours, up to 72, 96 and 120 hrs Track forecasts based on climatology, numerical models, and experience of forecaster © AMS

24 With lengthening forecast period, error increases.
Weather Prediction Atlantic hurricane track forecast error, and basin intensity forecast errors. With lengthening forecast period, error increases. 24 © AMS

25 Weather Prediction Forecasting Tropical Cyclones
SLOSH (Sea, Lake and Overland Surges from Hurricanes) model predicts location and height of storm surge Probability forecast included in advisory statements since 1983 Hurricane Watch: winds of at least 119 km (74 mi) possible within the next 36 hours Hurricane Warning: hurricane conditions expected in 24 hours or less Watches and warnings also issued for tropical storms 25 © AMS

26 Weather Prediction During the 20th century, tropical cyclone fatalities in the U.S. generally trended downward. Property damage has trended upward since the 1980s 26 © AMS

27 Weather Prediction Aviation Weather Center (AWC)
Located in Kansas City, MO Supports FAA Forecasts for aviation interests 27 © AMS

28 Weather Prediction Storm Prediction Center (SPC) Located in Norman, OK
Forecasts severe storms Also monitors fire weather, blizzards Convective outlooks identifying areas expected to experience severe and non-severe thunderstorms in 1-3 days. Issued several times a day Specify areas of severe thunderstorm risk 28 © AMS

29 SPC Day 1 convective outlook issued at 1259Z on 2 March 2012.
Weather Prediction SPC Day 1 convective outlook issued at 1259Z on 2 March 2012. © AMS

30 Weather Prediction River Forecast Centers (RFC)
13 centers located nationwide Develops river, reservoir, and flood forecasts Monitors and forecasts river discharge and stage Locations of River Forecast Centers. © AMS

31 Weather Prediction Marine Forecasting Space Weather Forecasting
Ocean Prediction Center located in Camp Springs, MD Issues forecasts, warnings, guidance for mariners, fisheries recreational boaters Space Weather Forecasting Space Weather Prediction Center (SWPC) located in Boulder, CO Monitors phenomena such as the aurora, solar wind, and solar cycle Scales used that rank severity from 1 to 5 © AMS

32 Weather Prediction Forecast Skill Declines rapidly after 48 hrs,
minimal beyond 10 days Missing or inaccurate observational data Failure to detect all mesoscale and micro-scale circulation systems Imprecise equations in numerical models 1-5 day forecasting Slow but steady improvement Better understanding of atmospheric processes Larger and faster computers More reliable and sophisticated observational tools Denser weather observational networks worldwide Tracking an early winter cyclone. © AMS

33 Weather Prediction Computers won’t replace meteorologists
The best forecasters rely on knowledge, experience, and intuition Begin with previous and current observations Must analyze and interpret computerized predictions Those forecasts are adapted to regional and local circumstances © AMS

34 Weather Prediction Long-Range Forecasting Climate Prediction Center
Monthly, seasonal and multi-seasonal generalized climate outlooks Long range forecasting relies on teleconnections Linkage between changes in atmospheric circulation occurring in widely separated regions of the globe 30-day (monthly) outlooks Relies on circulation patterns at 700 mb level Identifies areas of persistent warm and cold air advection 90-day (seasonal) outlooks Relies on long-term trends and recurring events Computer attempts to match past trends with present conditions 15-month (multi-seasonal) outlooks began in 1995 Each month 13 forecasts are issued, Each covers a 3-month period Subsequent 3-month forecast overlaps previous by 2 months © AMS © AMS

35 © AMS

36 Weather Prediction Single-Station Forecasting
Short-term weather prediction based on observations at one location Forecasts usually generalized and tentative Fair-weather bias Fair-weather days outnumber stormy days almost everywhere Predicting all fair-weather days would be correct more then half the time Persistence Weather episodes persist for some period of time (if it has been cold and storm for several days, it may continue that way for awhile) Climatology Forecast prepared based on previous years weather © AMS

37 Weather Prediction Private Sector Forecasting
Television and radio stations, some newspapers, and private forecast services Some private meteorologists tailor forecasts to specific needs of their commercial, agricultural, or industrial clients Supplement the efforts of government forecasters © AMS

38 Communication and Dissemination
NCEP maps and charts transmitted to local NWS Forecast Offices to guide meteorologists in preparing local forecasts Weather information then distributed to the public When hazardous weather threatens Outlooks: provided for advanced notice Watches: hazardous weather is possible based on current or anticipated conditions Advisories: anticipated weather hazards; less serious then those covered by warnings Warnings: hazardous weather is occurring in the region or imminent © AMS

39 Communication and Dissemination
NWS also issues Tornado Warning: detection of a thunderstorm that is known or likely to produce a tornado Heavy Snow Warning: snowfall of at least 10 to 15 cm (4 to 6 in.) expected in less then 12 hrs Blizzard Warning: blowing or falling snow with sustained winds of 56 km (35 mi) per hr or higher, reducing visibility to less then 400 m (1300 ft) Flash Flood Watch: flash flooding possible within watch area Flash Flood Warning: dangerously rapid rise in river level is imminent or occurring Public receives weather reports and forecasts via radio, NOAA weather radio, TV, Internet, newspapers © AMS


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