Weather

Inadvertant thunderstorm penetration

-Attitude of a/c: use attitude indicator to establish attitude for max endurance -Select altitude and heading (4000' to 6000' AGL is the area with the least turbulence) -Cockpit lights: bright -Airspeed: max endurance airspeed -Radio equipment: turn volume own -Do not turn back

Clouds associated with mountain wave

-Cap cloud (caps mountain range) -Lenticular (most familiar sign of wave conditions) -Rotor (dark ominous cloud)

Frost

-Forms by sublimation of water vapor on cold (below 0 degrees), clear nights -Tiny ice crystals -Should be removed from aircraft before takeoff

Mountain wave crossing procedure

-If practicable avoid completely -Avoid lenticular clouds, cap clouds, rotor clouds -Approach mountain range at 45 degrees angle at a high as possible altitude

Clear ice (0 to -10)

-Large supercooled water droplets -Lower cumuliform clouds and in freezing raing -Clear, solid ice -Blunt shape -Hard to break loose

Turbulence of mountain wave

-Usually most dangerous feature -Found on the lee side of mountain (most hazardous feature) -May extend downwind for several miles -Drafts may range from slight bumpiness to 6000 FPM -Helicopter, due to close proximity to surface are especially susceptible

Mature stage of thunderstorms

-Vertical currents: 6000 FPM up, 4000 FPM down -Temperature distribution: warmer in updraft areas and colder in downdraft -Turbulence: most severe in mid-altitude levels -Surface winds: strong and gusty -Precipitation: heavy rain showers

Dissipating stage of thunderstorms

-Vertical currents: all downward -Temperature distribution: colder in cloud than outside -Turbulence: moderate to severe -Surface winds: strong and gusty -Precipitation: heavy rain showers decreasing to light to none

Cumulus stage of thunderstorms

-Vertical currents: upward -Temperature distribution: warmer in cloud than outside -Turbulence: light to moderate -Surface winds: gusty and variable -Precipitation: none outside of cloud

Rime ice

(0 to -20 degrees) -Small water droplets (supercooled) -Stratiform clouds (0-20) and upper cumuliform below -10 to -20 -Rough deposit -Builds to a point -Easy to break loose

Characteristics of high-pressure systems

1. Vertical movement: sinking 2. Movement at surface is outward (divergence) 3. Usually associated with weak pressure gradient and weak winds 4. Visibility usually good but can be restricted due to fog, haze and smoke 5. Usually negligible turbulence near center or vicinity of ridge 6. Flying conditions: good

Frontal fog

1. Warm air forced aloft until precipitation falls 2. Falls through frontal inversion into colder air below, increasing dew point

Upslope fog

1. Warm moist air flowing up rising terrain 2. Cools adiabatically 3. May "cap" moutnains (10-15 knot wind) 4. Usually localized 5. May occur any time upslope adiabatic cooling occurs 6. Persistent

Advection fog

1. Warm, moist air flowing over a cool surface 2. Cool surface lowers temperature of lower layers of air to near dew point 3. Results from surface cooling 4. May occur at any time wind and temperature are favorable 5. Wind speeds up to 15 knots 6. Deep moving, widespread 7. Persistent

Consider fog formation at destination to be

1. When temperature and dew point are to be within 2 degrees 2. When field is near coast or large bodies and large amounts of nuclei are present 3. Check weather reports and forecasts 4. Pick good alternate 5. Consult forecaster

Moist adiabatic cooling rate

1.5 degrees C per 1000 feet. Occurs after saturation takes place in rising air

After LFC what does the lapse rate change to?

1.5, meaning that the cloud cools slower than the surrounding air

Slope of a cold front

1:80 (steep)

What is the altitude of friction level

2000 feet AGL. Above that level winds are Gradient Winds or Winds Aloft

Dry adiabatic cooling rate

3 degrees C per 1000 feet. Occurs when the air is rising and not saturated (no condensation)

SCT

3-4 octas. Not a ceiling

How often are winds and temperature aloft forecasts issued?

4 times per day

BKN

5-7 octas

OVC

8 octas.

Definitions of a front

A boundary between air masses of different densities

High pressure gradient winds (above friction level)

Gradient forces start the wind blowing directly across the isobars into the area of low pressure. Coriolis modifies gradient and causes clockwise flow parallel to the isobars

Low pressure gradient winds (above friction level)

Gradient forces start wind blowing directly across isobars into the area of lower pressure. Coriolis force modifies gradient and causes counterclockwise flow parallel to isobars.

GR

Hail

HZ

Haze

Advection

Horizontal transfer of heat by wind. The transfer of heat horizontally is somewhat greater than vertical transfer of heat

IC

Ice crystals

PL

Ice pellets

Temperature forecasts for winds and temperature aloft forecasts?

Lowest altitude where temperature is forecasted is 6000 feet MSL. Temperature forecasts are not issued for within 2500 feet of a location's elevation

Flight conditions encountered with cumulus and cumulonimbus

May be extremely violent, with turbulence, thunderstorms, microbursts, heavy precipitation, possible hair, tornadoes, icing, gusty surface winds, good visibility

Flight conditions encountered with stratus clouds

May extend over large areas causing low ceilings, poor visibility, light steady precipitation, little or no turbulence, icing, and light surface winds

BR

Mist

Mountain wave

Needs stable air with winds in excess of 25 knots blowing across a mountain range

Ceiling by definition

The lowest layer aloft reported as BKN or OVC. If the sky is totally obscured with ground based clouds, the vertical visibility is the ceiling.

Warm front occlusion

When cold front runs over hte warm front, it is called a warm-type occlusion. In this area the coldest air is ahead of the warm front. The warm air is lifted aloft and blocked from the surface

Temperature inversions

When temperature increases with altitude rather than decreases

Cold front occlusion

When the cold front runs underneath the warm front, it is called a cold-type. The coldest air is behind the cold front. Warm air of the warm front is lifted aloft and blocked from the surface

Flying with a left crosswind indicates...

Flying towards a low pressure center

FG

Fog

Cold front definition

The leading edge of a cold air mass normally moving to the southeast

FEW

1-2 octas. Not a ceiling.

Standard MSL pressure

1. 29.92 inches of mercury 2. 1013.2 millibars

Cooling processes

1. Adiabatic: most common, vertical development 2. Nocturnal: low clouds and fog 3. Advection: warm, moist air moving over a colder surface usually producing low clouds

Types of thunderstorms

1. Air mass 2. Frontal

Valley fog

1. Air on slopes cools rapidly at night, becomes more dense 2. Fills valley floor with cooler air, which, if cooled to its dew point, can form fog 3. Gradually deepends

Middle clouds (bases between 6500 and 18000)

1. Altostratus: As 2. Altocumulus: Ac

Radiation fog

1. At night terrestrial radiation cools the earth's surface. Surface cools lower layers of air to dew point 2. Light winds (2-5 knots) deepen cooling action 3. Usually localized 4. Tends to form between midnight and sunrise 5. Dissipates after sunrise

High clouds (bases greater than 18000)

1. Cirrus: Ci 2. Cirrostratus: Cs 3. Cirrocumulus: Cc

Steam fog

1. Cold air over warmer water 2. Water evaporates rapidly, increasing dew point 3. Common over lakes and rivers in fog

Frontal thunderstorms

1. Cold front 2. Squall line 3. Warm front

Air mass thunderstorms

1. Convection 2. Orographic

Categories of clouds

1. Cumulus 2. Stratus

Stages of thunderstorms

1. Cumulus stage 2. Mature 3. Dissipating/anvil

Low level clouds (bases less than 6500 feet)

1. Cumulus: Cu 2. Cumulonimbus: Cb 3. Stratus: St 4. Stratocumulus: Sc 5. Nimbostratus: Ns

Factors affecting fog dissipation

1. Heating 2. Strong wind 3. Greenhouse effect

Height of Troposhphere

1. Height at equator is approximately 60000 feet (hot air rises) 2. Height at poles approximately 25000 feet

Factors conducive to fog formation

1. High moisture content (spread within 2 degrees or less) 2. Condensensation nuclei 3. Cooling action

Semi-permanent pressure areas

1. High pressure tends to form over cooler areas (land in winter months, oceans in summer months) 2. Winter and summer months will cause pressure systems to vary slightly in latitude

Continental air masses are associated with good flying conditions, except for:

1. Intense surface heating may produce strong turbulence with gusts and blowing dust or sand (cTk) 2. Movement of cold, dry air over warm water may produce dense fog or low overcast skies with drizzle or snow

Hazards associated with icing

1. Loss of autorotative capability 2. Reduces lift 3. Increases drag 4. Increases weight 5. Decreases stall speed 6. Reduces visibility when ice forms on windshield 7. Reduces airflow to engines when ice forms on screens 8. Pitot and/or static source icing results in instrument error

Altitude of cloud type (nearest 100 AGL)

1. Low: bases up to 6500 feet 2. Middle: bases 6500 feet to 18000 feet 3. High: bases over 18000 feet

Names used to describe various types of clouds

1. Nimbus or nimbo: rain cloud 2. Alto: middle level clouds 3. Cirrus/cirro: high level clouds

Two types of temperature inversions

1. Nocturnal inversion: happening on cool clear night 2. Frontal inversion: where cold air lifts warmer air aloft

Air masses over the United States

1. North American High 2. Siberian High 3. Bermuda High

Stability factors

1. OLR less than moist adiabatic cooling rate (1.5) air will be stable 2. OLR greater than dry adiabatic cooling rate (3.0) air will be absolutely unstable 3. OLR between dry and moist adiabatic cooling rates (1.5 and 3.0) air will be conditionally unstable

Types of fog

1. Radiation fog 2. Advection fog 3. Upslope fog 4. Valley fog 5. Frontal fog 6. Steam fog 7. Ice fog

Formation of freezing rain

1. Rain falls from frontal inversion through wedge of polar air 2. Rain droplets freeze on aircraft as clear ice 3. Most common with warm fronts

Three stability conditions

1. Stable (air that resists vertical movement) 2. Unstable (air moving vertically) 3. Conditionally unstable

Frontal discontinuities

1. Temperature 2. Moisture content (dew content) 3. Pressure (fall then rise) 4. Wind shift (90 degrees)

Conditions affecting atmosphere circulation (three cell theory)

1. Uneven heating of earth's surface: land and water heat at different rates 2. Rotating earth causes Coriolis force 3. Tilt of the Earth on its axis

Conditions conducive to the development of thunderstorms

1. Unstable or conditionally unstable air 2. High moisture content (high dew point) 3. Lifting actions: convection, orographic or frontal

Characteristics of low-pressure systems

1. Vertical movement: rising 2. Movement at the surface: inward 3. Usually associated with strong pressure gradient/strong winds 4. Visibility limited by clouds, fog, precipitation 5. Can be associate with turbulence, in vicinity of sharp trough 6. Flying conditions: poor

Stationary front definition

A front which is not moving. Normally considered stationary with a speed of zero to less than 5 knots

Definition of atmosphere

A great envelope of air that surrounds the earth and rotate with it. Approximately one-half the air by weight is within the first 18000 feet

Definition of air mass

A large body of air whose physical properties (temperature and moisture) are horizontally uniform

Microburst

A short-lived, powerful downburst of air associated with convecti ve activity with diameters up to 1/2 mile, lasting 5-15 minutes

Dry microburst

A typical dry microburst is produced by cumulus cloud with little or no surface rain. If extremely dry, the storm will produce virga.

Moisture content as a factor in atmospheric stability

Air with high moisture content tends to be more unstable than dry air, if lifting action occurs

Level of Condensation

Altitude to which the air must be lifted for condensation to take place. Clouds will form at this altitude: temperature and dew point are the same

In which direction does gradient force act?

Always acts from high to low pressure, perpendicular to the isobars

Water vapor content: Relative humidity

Amount of water vapor in the air expressed ass a percent, compared to what it could hold at that temperature

Level of Free Convection

An altitude at which the temperature of the air inside the parcel of air being lifted becomes the same as the surrounding air. Any further lifting iwll cause the air inside the parcel to become warmer than the surrounding air and have its own lifting force. Thunderstorms may begin to form at this point

Ridge

An elongated area of high pressure

Trough

An elongated area of low pressure

Types of occlusions

Cold and warm. Name of occlusion is derived from which front as the colest air and affects the surface

Movement of open wave

Travels in an easterly direction along the line of the original front from which it is formed

High pressure patterns

Anticyclone: areas where pressure is higher than all surrounding pressure. Indicated by a closed system of isobars, pressure increasing toward the center

Ice fog

Any time fog forms in very cold temperature with abundant nuclei, tiny ice crystals are produced by sublimation (-25 or colder)

Low pressure patterns

Areas where pressure is lower than all surrounding pressure: indicated by a closed system of isobar pressure decreasing toward the center

Drift correction during frontal passage

As soon as you note a free-air temperature change, anticipate a drift correction to the right

Formation of open wave

Cold front weather associated with the cold front, warm front weather associated with warm front, and warm air in the open area between the two fronts. Winds in the open area are generally SW

North American High

Cold, dry air from Canada moving south, usually originates within the Arctic Circle

Slope of warm front

Average 1:200

Flight considerations for open wave

Avoid crest of wave and cold front portion.

BL

Blowing

Types of clouds associated with occlusions

Both warm and cold front types: stratiform and cumuliform

Bermuda High

Brings warm, moist air from the Gulf of mexico and causes precipitation in the summer months and fog in the winter

Lapse rate

Change in temperature with altitude. Standarad temperature lapse rate is 2/1000 feet

Indications of frontal passage (in flight)

Check OAT gauge

Flight procedures for air mass thunderstorms

Circumnavigate by at least 20 miles

Stratus clouds definition

Clouds with horizontal development; generally formed in stable air

Cumulus clouds definition

Clouds with vertical development formed by rising air. Tops may reach over 60,000 feet

Siberian High

Cold air from Siberia, changes to moist air over the North Pacific Ocean and enters the northwestern US as cold, moist air

"COR" meaning

Correction to previous report

Clouds associated with cold fronts

Cumuliform predominant

Flight considerations for cold fronts and squall lines

DON'T GO. Land and wait for it to pass.

"The spread"

Difference between temperature and dewpoint. Condensation may occur when the spread is 2 degrees C or less

DZ

Drizzle

Natural air

Dry air plus various amounts of water vapor and condensation nuclei

Composition of the atmosphere

Dry air-nitrogen 78%, oxygen 21%, other gases 1%

DU

Dust

DS

Dust storm

PO

Dust/sand swirls

When are TAFs valid?

Each TAF is valid for 24 hours, some TAFs are now being issued witha 30 hour valid. Prepared one-half hour prior to scheduled transmission times

How often are weather depiction charts transmitted

Every three hours

How frequently are surface analysis charts transmitted

Every three hours. Data is normally 2-6 hours old when used by an aviator in a weather station.

Obstructions include what?

FG, HZ, FU...etc

Flying with a right crosswind indicates...

Flying toward a high pressure

Coriolis force

Force developed by unequal speed of rotation of the earth's surface. Speed is greater at the equator than at the poles. Causes wind deflection.

Pressure gradient force

Force exerted by the change in pressure per unit of horizontal distance. This force causes the wind to blow

Formation of clouds

Formation is the direct result of saturation. Saturation is generally the result of cooling

FC

Funnel cloud

Flight considerations for warm fronts

General problems are low ceilings and poor visibilities. Fly below freezing levels and ensure sufficient fuel

Flight considerations for stationary front

General recommendation is the same as a warm front

RVR is given when?

Given in feet when prevailing visibility is 1 SM or less and/or the measured runway visibility for the designated instrument runway is 6000 feet or less

Winds and temperature aloft forecasts issued speeds

Given in knots (two digits): 1312 means the winds are from 120 at 12 knots

Low pressure surface winds (below surface level)

Gradient force becomes predominate and causes the surface wind to flow across isobars converging toward the low pressure. 30 degrees in counter-clockwise direction

FEW000, SCT000, or BKN000

Indicates less than full obscuration coveering 5/8 to 7/8 sky coverage

Definition of isobars

Lines connecting points of equal pressure corrected to sea level, usual spaced 4 mb apart

DR

Low drifting

Stability

Lower cased letter (themodynamic classification)

Moisture content classification code

Lower-case letters 1. c-Continental-formed over land, moisture content low 2. m-Maritime-formed over water, moisture content high

SKC

No clouds below 12000 feet

When is TAF preapred?

One-half hour prior to scheduled transmission times

P versus R prefix on RVR reportable values?

P indicates a value higher or an M to indicate a value lower than RVR reportable values (V means variable)

PR

Partial

BC

Patches

Two types of frontal fog

Prefrontal and postfrontal

Cause of frontal weather

Primary cause of frontal weather is the lifting of warm moist air by colder air. Therefore all fronts have a temperature inversion.

Wet microburst

Produced by cumulus cloud with heavy rain

Indications of frontal passage (ground)

Pronounced wind shift and change in air temperature, note a change in dew point and barometric pressure

Methods of heat transfer

Radiation, conduction, convection, advection

RA

Rain

Primary factors affecting frontal weather

Slope and speed, moisture content and stability

FU

Smoke

SN

Snow

SG

Snow grains

GS

Snow pellets/small hail

Types of icing

Rime ice, clear ice, frost

SA

Sand

SS

Sandstorm

MI

Shallow

SH

Showers

Movement of occlusion front

Similar to an open wave, movement to the east

Slope of stationary front

Similar to warm front (1:200)

Formation of occlusions

Since cold fronts move faster than warm fronts, the cold portion of the open wave will overtaked the warm front portion. The cold front either runs underneath or over the warm front. The warm air sector is blocked away from the surface and one of the fronts is lifted aloft

PY

Spray

SQ

Squalls

"w" stability classification

Stable, air is warmer than the surface: 1. Horizontal development type clouds and possible fog 2. Low ceilings 3. Poor visibility 4. Smooth, stable air with little or no turbulence 5. Occasional light continuous drizzle or rain

Buys Ballot Law

Standing with your back to the wind, in the northern hemisphere, the low will be on your left

Clouds associated with warm front

Stratiform predominant

FZ

Supercooled/freezing

High pressure surface winds (below friction level)

Surface friction decreases wind speed which decreases Coriolis force. Diverges wind at an angle of 30 degrees (still in the clockwise direction)

TAF

Terminal Aerodrome Forecast

Water vapor content: Saturation

The air has all the water vapor it can hold at that temperature. The capacity of air to hold water vapor doubles for every 20 degrees farenheit increase in temperature

The results of coriolis force

The force acts perpendicular to the right of the wind. It is the greatest at the poles and zero at the equator. The force becomes equal and opposite of the gradient force and deflects the wind to flow parallel to the isobars.

Which prevailing winds affect the United States

The prevailing westerlies

Occluded front definition

The result of a faster moving cold front overtaking a slower moving warm front. The effect is one front on top of the other squeezing warm air between

Water vapor content: Dew point

The temperature to which the air must be cooled for it to become saturated and for a cloud to form. The higher the dew point, the more water vapor is present in the air

Radiation

The transfer of heat by electromagnetic waves: 1. Insolation-incoming from the sun (short wave) 2. Terrestrial-outgoing from the sun (long wave)

Winds associated with occlusions

The winds ahead of an occlusion may vary from south to east, but are generally from the SE. Winds behind an occluded front will generally be from the NW.

Which direction to cold air masses move?

They move south of their source origins

What type of winds does a weak pressure gradient force create?

This results in light or calm winds and is generally associated with high-pressure systems

What type of winds does a steep gradient force create?

This results in strong winds and is generally associated with low pressure

TS

Thunderstorms

+FC

Tornado/waterspout

Warm front definition

Trailing edge of a cold air mass moving generally to the northeast, being overridden by warmer air

Conduction

Transfer of heat by physical contact.

Convection

Transfer of heat by way of a gas in a vertical movement

Weather associated with warm front

Type: low ceilings, poor visibility, rain, drizzle, fog, scattered or embedded thunderstrms, possible clear ice and/or freezing rain Coverage: wide spread, 400-600 miles ahead of surface position Winds: generally from the SW behind and from the SE ahead of front Movement: to the NE Speed: average 15 knots

Weather associated with cold fronts

Type: post frontal, violent Coverage: critical area is 50 miles wide Winds: from the NW behind the front, from the SW ahead of the front Movement: to the SE Speed: average 25 knots. If faster, squall lines will form

Weather associated with stationary front

Type: similar to warm front Coverage: large area similar to warm front Winds: except in areas of showers, winds are light and variable, but generally tend to parallel the front in opposite directions Movement: unpredictable Speed: 0 to 5 knots

The movement of air over the surface of the earth is caused by ___________

Uneven heating. Changes in temperature and density causes air to be warmed at the equator and rises. Air flows toward the poles, air cooled at poles and descends flows toward the equator.

UP

Unknown precipitation

"k" stability classification

Unstable, air is colder than the surface: 1. Vertical development type clouds 2. Generally good ceilings (except with precipitation) 3. Excellent visibility 4. Pronounced instability (turbulence) 5. Occasional local thunderstorms, heavy showers, hail, snow flurries

Temperature

Upper-case letter 1. A-source region Arctic, temperature is the coldest 2. P-source region Polar, temperature is cold 3. T-source region Tropical, temperature is warm 4. E-source region, Equatorial, temperature is warmest

Freezing rain definition

Visible moisture and below freezing temperatures

Definition of fog

Visible moisture with base below 50 feet and no visible downward motion (above that is a cloud)

VA

Volcanic ash

Which direction do warm air massees move?

Warm air masses move north out of their source regions

Clouds associated with stationary front

Warm front type: stratiform

Definition of open wave

Wave-like appearance on the weather map with one portion of a cold front and the other a warm front with an open area in between

Weather associated with occlusion fronts

Weather combines widespread low ceiling and poor visibilities and severe weather. Most severe occurs in the early stages of the occlusion. This is the most violent front.

Frontal formation

When two high pressure cells exist so that the circulation of air is converging between them, a front is formed. Due to circulation around these cells, the warmer air from one cell is meeting colder air from the other. Converging air currents veer upward creating a zone of low pressure

Wind direction is in reference to which type of north?

Wind direction is in reference to TRUE north and is reported to the nearest 10 degrees

Flight considerations for occluded fronts

Worst possible weather. Avoid apex by at least 50-100 miles. Wait, circumnavigate, or fly through the warm or stationary front seperately

Layers of the atmosphere

a. Troposphere (closest to earth) b. Tropopause (boundary zone) c. Stratosphere (above troposphere)

Frontal thunderstorms

land