15. Weather Flashcards by Dennis Turney

When is a sea breeze most suitable for soaring?

Sea breeze = wind from ocean to shore
In afternoon when land is hotter than water.

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If a flight is made from low pressure to high pressure without the altimeter being reset, the altimeter will indicate?

Lower than actual altitude

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CONDITION most conducive to frost formation?

Surface temp below freezing & air temp is below freezing
Sublimation = solid to gas without passing thru liquid state.
Frozen dew is hard and transparent.
Frost is white and opaque.

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Conditions resulting in frost?

Collecting surface at or below dewpoint of adjacent air. AND
Dewpoint is below freezing.

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If outside air temp at a given altitude is warmer than standard, then the density altitude is

higher than pressure altitude

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Weather condition beneath a low level temp inversion layer when the relative humidity is high?

Smooth air, poor visibility, fog, haze, low clouds

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An air mass moving inland from the coast in winter is likely to result in

Fog
Advection fog Advection happens over land AND water. Radiation is only land.

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What is absolute altitude?

Altitude above ground level

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Stable air mass characteristics

Stratiform clouds & fog
Continuous precip
Smooth air
Fair to poor visibility

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Unstable air mass characteristics

Thunderstorms
Cumuliform clouds
Showery precip
Rough air -turbulence
Good visibility

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Why is frost hazardous to flight?

Spoils smooth air flow over wind and decreases lift

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Clouds, fog, or dew will always form when

Water vapor condenses

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Temperature inversion results in what weather condition?

An increase in temp as altitude increases

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An almond or lens shaped cloud that appears stationary but can have winds of 50 knots or more is called?

Lenticular

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What condition would tend to increase density altitude at a given airport?

An increase in air temp

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Unstable air mass approaching. Which would not be a concern?
Thunderstorms, turbulent air, stratiform clouds

stratiform clouds

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Relationship of strong thermal to sink between them.

Strong thermal = High sink

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If temp and dewpoint spread is small and decreasing and the air temp is 62F, what type of weather is likely to develop?

Fog or low clouds

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Moist stable air flowing upslope can be expected to ?

Stratus type clouds. Upslope fog
Warm stable air up slope = stratiform
Warm unstable air up slope = cumuliform

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Condition when indicated altitude = true altitude

At sea level with standard conditions.
29.92 & 59F
When altimeter is adjusted to actual barometric pressure.

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Steady precipitation preceding a front is an indication of

Stratiform clouds with little turbulence.
Stable Warm air overriding a front = stratiform
Unstable Warm air overriding a front = Cumuliform

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Moisture is added to air by what two processes?

Evaporation and sublimation

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Boundary between 2 air masses =

Front

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Nimbus referring to a cloud means

rain cloud

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Situation conducive to formation of radiation fog?

Warm moist air over flatland areas on clear calm nights

When is advection fog most likely to form

Air mass moving inland from the coast in winter

Advection fog

Layer of warm moist air moves over a cold surface

Upslope fog

Moist air moves up a slope. Stable air = Stratus Unstable air = Cumuliform Requires wind to form

Steam Fog / Sea Fog

Cold dry air mass moves over warm water. Resembles smoke Coldest month of the year Low level turbulence & icing

Ice Fog

When weather is much below freezing (-25F) and water vapor turns directly into ice crystals.

Stable air characteristic? Stratiform clouds, Unlimited visibility, Cumulus clouds

Stratiform clouds

Crests of standing mountain waves may be marked by stationary lens shaped clouds known as

standing lenticular

The amount of water vapor air can hold depends on

Air Temperature

Clouds are divided into 4 families according to their

Height range

Where and under what condition can lift be found in stable conditions?

Upwind side of slopes when sufficient wind is present

What is density altitude?

Pressure altitude corrected for non standard temperature

When warm moist stable air flows upslope it produces

Stratus clouds

Which feature is associated with a temp inversion? unstable layer of air, chinook winds on mtn slopes, stable layer of air

Stable layer of air

Stable air mass? poor surface visibility, showery precip, turbulent air

Poor surface visibility

How to obtain pressure altitude for flights below 18000 MSL?

Set Kolsman window to 29.92

What measurement can be made to determine the stability of the atmosphere?

Actual lapse rate. In high lapse rate = unstable Low lapse rate = stable If you are surrounded by an air mass that has a high lapse rate, then any local heating of the ground will allow thermals to develop. If surrounding lapse rate is low, then thermals from local heating will be weak.

What is the std lapse rate?

2C / 1000' A high lapse rate indicates greater than normal change in air temp with altitude and is characteristic of Unstable Air

What is the DALR?

Dry adiabatic lapse rate = 3.0C / 1000'

Std T & P at sea level?

29.92 " Hg 59F 1013.2 millibars 15C

In flight condition for structural icing to form? visible moisture, small temp/dewpoint spread, stratiform clouds

Visible moisture & temp at or below 32F

Highest accumulation rate of structure icing? Freezing rain, freezing drizzle, cumulus clouds with below freezing temp

Freezing rain Supercooled water freezes on impact with plane. Thunderstorms can create supercooled rain. large supercooled droplets make clear icing very rapid between 0C - -15C

Unstable air? Stratiform clouds, good visibility, poor visibility

good visibility

Clouds, fog, and dew will always form when

water vapor condenses

Weather feature will always occur when flying across a front? stability, type of precip, wind direction

wind direction

What types of fog depends on wind to exist?

Advection and upslope fog

Development of thermals depends on

solar heating

What is dewpoint?

The temp that air must be cooled to become saturated

The most frequent type of surface based temp inversion is produced by

Terrestial radiation on a clear calm night. Ground radiates heat and cools faster than surrounding air

Convective circulation patterns associated with sea breezes are caused by?

Land absorbing and radiating heat faster than the water. Sea breeze = breeze from the sea = afternoon

True altitude = ?

Vertical distance between plane and sea level

One of the most easily recognized discontinuities across a front are? increase in cloud coverage, increase in RH, change in temp

Change in temp Types of fronts referencing new air to the air its replacing 1. Warm 2. Cold 3. Stationary 4. Occluded

What would decrease the stability of an air mass?

Heating from below

Mtn wave turbulence could be anticipated when 40 knot or higher winds blow? parallel to mtn and air is stable, across mtn range and air is stable down a mountain valley and air is unstable

Across a mtn range and air is stable

At 5000' AGL winds are SW. At ground level winds are South. Diff in direction is due to

Friction between the wind and the surface. SFC slows wind. The more rough the terrain the more it affects direction and speed. Coriolis force deflects air to the right in Northern hemisphere

A pilot can expect wind shear zone in a temp inversion when the wind speed at 2000' - 4000' AGL is ?

25 knots

What signals the BEGINNING of a mature stage of a thunderstorm?

Precipitation begins to fall. 1. Cumulus stage - clouds increase in vertical height 2. Mature stage - Rain forms and starts falling. Condensing action reduces temp causing downdrafts. Most violent part of thunderstorm. 3. Dissipating - Anvil shape cloud. Downdrafts take over spreading surface winds and lower temps

Every physical process of weather is accompanied by or is the result of ?

Heat exchange

What to do when landing with icing conditions?

Fly faster than normal landing & approach speeds

The evidence of ice pellets at the surface is evidence that there is ?

a temp inversion with freezing rain at a higher altitude

Under what conditions will pressure altitude and true altitude be the same?

When standard atm conditions exist

Where does wind shear exist?

At all altitudes in all directions horizontal and vertical.

What causes variations in altimeter settings between weather reporting stations?

Unequal heating of atmosphere