Presentation on theme: "Instrument Ground School Basic Weather"— Presentation transcript:
1 Instrument Ground School Basic Weather Authored By Lt Colonel Garrett L. Sager 30-Jan-2006TX-129 Fort Worth Senior Squadron Modified by Lt Colonel Fred Blundell TX-129 Fort Worth Senior Squadron For Local Training Rev Jan-2014
2 This Training Slide Show is a project undertaken by Lt Colonel Fred Blundell of the TX-129 Fort Worth Senior Squadron, Fort Worth, TX for local use to assist those CAP Members interested in advancing their skills. The information contained herein is for CAP Member’s personal use and is not intended to replace or be a substitute for any of the CAP National Training Programs. Users should review the presentation’s Revision Number at the end of each file name to ensure that they have the most current publication.
3 Instrument Ground School Weather OverviewHazards to FlightCauses & Types of WeatherSources of Information
4 Instrument Ground School Weather OverviewAs pilots, we deal with weather every time we fly.As Instrument Pilots, our knowledge of weather must be more in depth than VFR pilots.
5 Instrument Ground School Weather Hazards to Flight“Most Weather is Flyable” – Robert BuckThere are 3 principle Weather Hazards can really get you into trouble:Low Visibility / CeilingsThunderstormsIce
6 Instrument Ground School Weather Causes of WeatherAll weather processes are directly associated with the exchange of heatAs an example, updrafts, caused by solar heating of the surface, cause cumulus clouds as the air raises and the moisture condenses, releasing the heat absorbed at the surface.
7 Instrument Ground School Weather Causes of WeatherUnequal heating of the Earth’s surface causes differences in temperature & pressure (and altimeter settings)Points of equal pressure are connected on weather maps using lines called “isobars”Wind flows from high-pressure to low pressure.Flow is perpendicular to isobars
9 Instrument Ground School Weather Causes of WeatherCoriollis force deflects wind to the right in Northern hemisphere.Earth rotates under the wind, causing an apparent change in wind direction.Coriollis force acts perpendicular to wind direction, and is proportional to wind speedIt deflects wind so strongly that wind subsequently flows parallel to isobars.
10 Instrument Ground School Weather Causes of WeatherCoriollis force deflects wind to the right in Northern hemisphere.It’s greater at higher altitudes, since wind near the surface (below 2000 AGL) is slowed back friction.Since surface winds are slower, they are less effected by Coriollis force.Near the surface, the pressure gradient may be stronger than Coriollis force, causing the wind to flow across the isobars.
11 Instrument Ground School Weather Layers of the AtmosphereTroposphereFrom the surface to the “tropopause”, the boundary between the troposphere & stratosphere.Most of our weather occurs in the troposphereHeight of tropopause varies from about 25,000 feet near the poles, to about 37,000 feet in the mid-latitudes, to about 65,000 at the equator.
12 Instrument Ground School Weather Layers of the Atmosphere
13 Instrument Ground School Weather Layers of the AtmosphereTroposphereAt the tropopause, temperature and wind vary greatlyAn abrupt change in the temperature lapse rate occurs at the tropopauseUp to the tropopause, temperature decreases with altitudeAbove the tropopause, temperature is constant with altitude.
14 Instrument Ground School Weather Layers of the AtmosphereStratosphereLayer above the troposphereLow moisture, and few cloudsTemperature remains relatively constant with altitude in the stratosphere.This creates a temperature inversion.Only the most powerful thunderstorms have sufficient energy to climb into the stratosphere.
15 Instrument Ground School Weather Layers of the AtmosphereJet Stream – a narrow, disjointed, wandering “river” of air.Flows from west to east, near the tropopauseBy definition, has speeds > 50 ktWeaker & farther north during summerStronger & farther south during winterMoves with pressure ridges & troughs.
16 Instrument Ground School Weather Air MassesAir Masses are large regions of air with uniform temperature and moisture properties.The boundary between air masses is called a “front”.A “warm front” occurs when a warmer air mass overtakes a cooler oneA “cold front” occurs when a cooler air mass overtakes a warmer one.
17 Instrument Ground School Weather Air Masses - StabilityLapse Rate – the change in temperature with altitude“Adiabatic” lapse rate is the temperature change due to expansional cooling.Dry adiabatic lapse rate is 3C per 1000 ftAdiabatic lapse rate varies from 1.1C to 2.8C, depending on moisture contentAverage adiabatic lapse rate is 2C per 1000 ft.
18 Instrument Ground School Weather Air Masses - StabilityLapse rate can be used to gage atmospheric stability.Actual lapse rate is sometimes referred to as “ambient” lapse rate – average 2C per 1000 ftLapse rate > 2C per 1000 ft, combined with high humidity indicates an unstable atmosphere, and thunderstorms are likely.Moist air is less stable than dry air, because it cools more slowly with altitude, so it must rise higher to cool.
19 Instrument Ground School Weather Air Masses - StabilityCloud Formation due to liftingDetermined by the stability of the air before lifting.Turbulence & cumuliform clouds (vertical development) are created when unstable air rises.Stable air lifted by mountain slopes creates stratiform clouds.Unstable air lifted by mountain slopes creates cumuliform clouds.
20 Instrument Ground School Weather Air Masses - StabilityStable AirStratiform Clouds & FogSmooth AirSteady PrecipitationFair – poor visibility, due to haze & smoke
21 Instrument Ground School Weather Air Masses - StabilityUnStable AirCumuliform CloudsTurbulent AirShowery PrecipitationGood Visibility (outside of clouds)
22 Instrument Ground School Weather Air Masses - StabilityCold air moving over warm surface results in turbulence, cumuliform clouds and good visibilityThis is due to the cold air being heated by surface, creating instability and lifting actionPrecipitation growth rate is enhanced by lifted, moisture laden air currents that condense, increasing droplet size.
23 Instrument Ground School Weather Air MassesFrontsWind changes across a frontWind shear may occur ahead of a warm front.Wind shear may occur just after a cold front passesSquall lines may develop ahead of a cold frontFrontal waves and low-pressure cyclones usually from in slow moving cold fronts, or stationary fronts
34 Instrument Ground School Weather Temperature InversionsA temperature inversion is when temperature increases or remains constant with altitude, rather than decreases.Results in warm, stable air below the inversionMay develop near the ground on cool, clear nights with light wind, due to terrestrial radiation.Stability results in smooth air, and haze, fog or low clouds.
35 Instrument Ground School Weather Temperature & DewpointThe ability of the air to hold moisture is directly related to it’s temperature.Warm air holds more moisture than cold airThe temperature at which the air is 100% saturated is called the “dew point”.If the air temperature is within 3C (5F) of the dewpoint and is decreasing, expect low clouds and fog to form.
36 Instrument Ground School Weather Temperature & DewpointFrost may form on a surface, if the surface temperature is below the dew point and the dew point is below freezing.Water vapor is visible when it condenses into clouds, fog or dew.Evaporation is when liquid water converts to vaporSublimation is when ice converts directly to vapor.
37 Instrument Ground School Weather FogRadiation Fog occurs with clear skies, little wind, and small temperature – dew point spread over land – usually low flat areasGround cools faster than air, cooling air very close to surface, resulting in a temperature inversion.
38 Instrument Ground School Weather FogAdvection Fog forms when warm moist air, usually from over a large body of water, moves over cool land.Requires WindOften happens in coastal areasUpslope Fog results from warm, moist air being forced up sloping terrain.
39 Instrument Ground School Weather FogPrecipitation Induced FogCaused by warm air dropping rain into cooler air beneathEvaporation from the precipitation saturates cooler air below, causing fog.Occurs easily in industrial areas, where pollution creates an abundance of nuclei for the moisture to condense onto.
40 Instrument Ground School Weather Cloud FamiliesHigh CloudsIce crystals – little threat of aircraft icing.Middle CloudsLow CloudsClouds with extensive vertical development.Cumulus, cumulonimbus
41 Instrument Ground School Weather Cloud FamiliesStanding Lenticular Altocumulus clouds (ACSL) are lens-shaped, and form on the downwind side of mountain ridges.Indicate very strong turbulence
42 Instrument Ground School Weather Cumulus CloudsCumulus clouds occur in unstable, moist air with a lifting action.Turbulence occurs at & below cloud level“Nimbus” means rain cloudTower cumulus is an early sign of cumulonimbusCumulonimbus Clouds (thunderstorms) contain the greatest turbulence.
43 Instrument Ground School Weather Thunderstorms3 stage life cycleCumulus – the building stage.Towering Cumulus, with continuous updraftsMatureGreatest Intensity, both updrafts & downdraftsDissipatingContinuous downdrafts, raining out.
47 Instrument Ground School Weather ThunderstormsProduces wind shear turbulenceIf penetrating a thunderstorm, fly straight ahead, set power for turbulence penetration speed, and try to maintain level attitude.Do not turn around – turn increases load factor on airplaneNo not try to maintain altitudeSevere Thunderstorms should be avoided by at least 20 miles.May cause turbulence and hail miles from the storm.
48 Instrument Ground School Weather Thunderstorms“Squall Line” is a non-frontal, narrow band of thunderstorms forming ahead of a cold frontMost severe conditions – hail, turbulence, tornados, etc.A “squall” is defined as a sudden increase in wind speed of at least 16 kts up to 22 kts, lasting for more than 1 minute.
49 Instrument Ground School Weather ThunderstormsEmbedded thunderstorms are storms that are obscured by cloudy conditions, haze layers, etc.Visual “see & avoid” may be inadequate“Spherics” or weather radar are essential to avoiding embedded thunderstorms.Radar detects precipitation, not instrument conditions.
50 Instrument Ground School Weather IcingTests indicate that frost, snow or ice with texture similar to coarse sandpaper reduces lift by up to 30%, and increased drag by up to 40%.“Freezing Level” is the altitude where freezing temperatures exist.Can be determined using the average lapse rate of 2C per 1000 ft.
53 Instrument Ground School Weather IcingRequires 2 conditionsVisible MoistureTemperature at or below freezingFreezing rain results in the fastest and greatest accumulation of ice.Indicates warmer temperatures above – temperature inversion.
55 Instrument Ground School Weather IcingIce pellets caused by rain freezing at higher altitudeHeavy, wet snow means temperature is above freezing at your altitude.It formed above you, but is on the verge of meltingFrost on the wings disrupts the flow over the wings, and should be removed before flight.