Authored By Lt Colonel Garrett L. Sager 30-Jan-2006 Modified by Lt Colonel Fred Blundell TX-129 Fort...

INSTRUMENT GROUND SCHOOL

BASIC WEATHER

Authored By Lt Colonel Garrett L. Sager 30-Jan-2006

TX-129 Fort Worth Senior SquadronModified by Lt Colonel Fred BlundellTX-129 Fort Worth Senior Squadron

For Local Training Rev 5.0 02-Jan-2014

1

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.

Instrument Ground School Weather

WeatherOverviewHazards to FlightCauses & Types of WeatherSources of Information

3

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.


4

Hazards to Flight“Most Weather is Flyable” – Robert BuckThere are 3 principle Weather Hazards can

really get you into trouble:○ Low Visibility / Ceilings○ Thunderstorms○ Ice


5

Causes of WeatherAll weather processes are directly associated

with the exchange of heat○ As 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.


6

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

7


8


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 speed○ It deflects wind so strongly that wind

subsequently flows parallel to isobars.

9


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.

10


Layers of the AtmosphereTroposphere

○ From 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.

11


Layers of the Atmosphere

12


Layers of the AtmosphereTroposphere

○ At the tropopause, temperature and wind vary greatly

○ An 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.13


Layers of the AtmosphereStratosphere

○ Layer above the troposphere○ Low moisture, and few clouds○ Temperature 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.

14


Layers of the AtmosphereJet Stream – a narrow, disjointed, wandering

“river” of air.○ Flows from west to east, near the tropopause○ By definition, has speeds > 50 kt○ Weaker & farther north during summer○ Stronger & farther south during winter○ Moves with pressure ridges & troughs.

15


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 one○ A “cold front” occurs when a cooler air mass

overtakes a warmer one.

16


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 content○ Average adiabatic lapse rate is 2C per 1000 ft.

17


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.

18


Air Masses - StabilityCloud Formation due to lifting

○ Determined 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.

19


Air Masses - StabilityStable Air

○ Stratiform Clouds & Fog○ Smooth Air○ Steady Precipitation○ Fair – poor visibility, due to

haze & smoke

20


Air Masses - StabilityUnStable Air

○ Cumuliform Clouds○ Turbulent Air○ Showery Precipitation○ Good Visibility (outside of clouds)

21


Air Masses - StabilityCold air moving over warm surface results in

turbulence, cumuliform clouds and good visibility○ This 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.

22


Air MassesFronts

○ Wind changes across a front○ Wind shear may occur ahead of a warm front.○ Wind shear may occur just after a cold front

passes○ Squall lines may develop ahead of a cold front○ Frontal waves and low-pressure cyclones

usually from in slow moving cold fronts, or stationary fronts

23


Fronts

24


Fronts

25


26

Fronts


27

Fronts


28

Fronts


29

Fronts


30

Fronts


31

Fronts


32

Fronts


33

Fronts


Temperature InversionsA temperature inversion is when temperature

increases or remains constant with altitude, rather than decreases.○ Results in warm, stable air below the inversion○ May 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.

34


Temperature & DewpointThe ability of the air to hold moisture is directly

related to it’s temperature.○ Warm air holds more moisture than cold air○ The 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.

35


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

vapor○ Sublimation is when ice converts directly to

vapor.

36


FogRadiation Fog occurs with clear skies, little wind,

and small temperature – dew point spread over land – usually low flat areas○ Ground cools faster than air, cooling air very

close to surface, resulting in a temperature inversion.

37


FogAdvection Fog forms when warm moist air, usually

from over a large body of water, moves over cool land.○ Requires Wind○ Often happens in coastal areas

Upslope Fog results from warm, moist air being forced up sloping terrain.

38


FogPrecipitation Induced Fog

○ Caused by warm air dropping rain into cooler air beneath

○ Evaporation 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.

39


Cloud FamiliesHigh Clouds

○ Ice crystals – little threat of aircraft icing.Middle CloudsLow CloudsClouds with extensive vertical development.

○ Cumulus, cumulonimbus

40


Cloud FamiliesStanding Lenticular Altocumulus clouds (ACSL)

are lens-shaped, and form on the downwind side of mountain ridges.○ Indicate very strong turbulence

41


Cumulus CloudsCumulus clouds occur in unstable, moist air with

a lifting action.○ Turbulence occurs at & below cloud level○ “Nimbus” means rain cloud○ Tower cumulus is an early sign of

cumulonimbusCumulonimbus Clouds (thunderstorms) contain

the greatest turbulence.

42


Thunderstorms3 stage life cycle

○ Cumulus – the building stage. Towering Cumulus, with continuous

updrafts○ Mature

Greatest Intensity, both updrafts & downdrafts

○ DissipatingContinuous downdrafts, raining out.

43


Thunderstorms

44


ThunderstormsAlways has lightning, since lightning causes

thunder.Produced by cumulonimbus clouds, and occur

with○ Water Vapor○ Unstable Lapse Rate○ Lifting Action

45


46

Thunderstorms


ThunderstormsProduces wind shear turbulence

○ If 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 altitude

Severe Thunderstorms should be avoided by at least 20 miles.○ May cause turbulence and hail miles from the storm.

47


Thunderstorms“Squall Line” is a non-frontal, narrow band of

thunderstorms forming ahead of a cold front○ Most 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.

48


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.

49


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.

50


Icing

51


52

Icing


IcingRequires 2 conditions

○ Visible Moisture○ Temperature at or below freezing

Freezing rain results in the fastest and greatest accumulation of ice.○ Indicates warmer temperatures above –

temperature inversion.

53


54

Icing


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.

55


Weather InformationFlight Service DUATS“The Weather Channel”Internet Sources

○ NOAA / ADDS○ Intellicast○ FOUS

56


Reading:Aviation Weather Gleim Study Unit 8: Aviation Weather

57


Questions?

Always Think Safety!58


Authored By Lt Colonel Garrett L. Sager 30-Jan-2006 Modified by Lt Colonel Fred Blundell TX-129 Fort...

Documents

Transcript of Authored By Lt Colonel Garrett L. Sager 30-Jan-2006 Modified by Lt Colonel Fred Blundell TX-129 Fort...