Fundamentals of Weather

Question 1

At what rate does atmospheric pressure decrease with an increase in altitude?

Answer 1

At a rate of approximately 1”Hg per 1,000 feet

Question 2

What are the standard temperature and pressure values for sea level?

Answer 2

15 degrees Centigrade and 29.92” Hg

Question 3

State the general characteristics in regard to the flow of air around high and low pressure systems in the northern hemisphere?

Answer 3

Low pressure - air flows inward, upward, and counterclockwise

High Pressure - air flows outward, downward, and clockwise

Question 4

What causes the winds aloft to flow parallel to the isobars?

Answer 4

The coriolis force causes winds aloft to flow parallel to the isobars

Question 5

Why do surface winds generally flow across the isobars at an angle?

Answer 5

Surface friction

Question 6

When temperature and dew point are close together what type of weather is likely?

Answer 6

Visibile moisture in the form of clouds, dew, or fog

Question 7

What factor primarily determines the type and vertical extent of clouds?

Answer 7

The stability of the atmosphere

Question 8

What is the difference between a stable and unstable atmosphere?

Answer 8

Stable resists any upward or downward displacement.

An unstable allows upward or downward disturbances to grow into a vertical or convective current.

Question 9

How do you determine the stability of the atmosphere?

Answer 9

When temperature decreases uniformly and rapidly as you climb, you have an indication of unstable air. If the temperature remains unchanged or decreases only slightly with altitude, the air tends to be stable. When air near the surface is warm and moist, expect instability.

Question 10

List the effects of stable and unstable air on clouds, turbulence, precipitation, and visibility

Answer 10

Clouds - S - stratiform - U - cumuliform
Turbulence - S- smooth - U - rough
Precip - S- steady - U -Showery
Vis - S - fair to poor - U - good

Question 11

What are the main types of icing an aircraft may encounter?

Answer 11

Structural, induction, and instrument

Question 12

Name the three types of structural ice

Answer 12

Clear - forms when large drops strike aircraft surface and slowly freeze

Rime - small drops strike and freeze rapidly

Mixed - combination of rime and clear, rough accumulation, intermingled with snow or ice

Question 13

What are the intensity categories of aircraft structural icing?

Answer 13

Trace - rate of accumulation slightly greater than sublimation, anti ice equip. not used unless encountered for extended period of time
Light - rate of accumulation may create problem if flight is prolonged. Occasional use of anti ice removes or prevents accumulation
Moderate - the rate of accumulation is such that even short encounters become potentially hazardous. use of anti ice or diversion necessary.
Severe - rate of accumulation is greater than anti ice ability to remove, immediate diversion necessary

Question 14

What is the definition of the term freezing level and how can you determine where it is?

Answer 14

Lowest altitude in the atmosphere over a given location at which that air temperatures reaches freezing.

Icing forecasts and PIREPS, Area forecasts, AIRMETs, SIGMETs, and low level significant weather charts are examples

Question 15

What factors must be present for a thunderstorm to form?

Answer 15

A source of lift
Unstable air
High moisture content

Question 16

What are squall line thunderstorms?

Answer 16

A non frontal, narrow band of active thunderstorms. Frequently develop ahead of cold front in moist, unstable air. Most intense weather hazard to aircraft.

Question 17

State two basic ways that fog may form?

Answer 17

By cooling air to the dew point

By adding moisture to the air

Question 18

What are the 5 types of fog?

Answer 18

Advection
Ice Fog
Radiation
Upslope
Precipitation induced fog

Question 19

What causes radiation fog to form?

Answer 19

Clear sky, little or no wind, small temp-dew point spread (high relative humidity). forms almost exclusively at night or near daybreak.

Question 20

What is advection fog and where is it most likely to form?

Answer 20

Forms when moist air moves over colder ground or water. Most common along coastal areas but often develops deep in continental areas. May occur with winds, cloudy skies, over wide geographic area, at any time. It deepens as wind speed increases up to about 15 knots. Stronger wind lifts fog into layer of low stratus of stratocumulus.

Question 21

Define upslope fog.

Answer 21

Forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the upslope wind ceases, the fog dissipates. Unlike radiation fog, it can form under cloudy skies. it is most common along eastern slopes of the Rockies. Can be dense and extend to high altitudes.

Question 22

Define ice fog.

Answer 22

Occurs in cold weather when the temperature is much below freezing and water vapor sublimates directly as ice crystals. Same conditions as radiation fog but temps are usually -25 °F or colder. It occurs mostly in arctic regions, but is not unknown in middle latitudes during the cold season.

Question 23

What is precipitation induced fog?

Answer 23

When relatively warm rain or drizzle falls through cool air, evaporation from precip saturates the cool air and forms fog. Dense and can continue for extended time period. Commonly associated with warm fronts, but can occur with slow moving cold fronts and with stationary fronts.

Question 24

Other than fog, what are several other examples of IFR weather producers?

Answer 24

Low clouds (stratus), haze, smoke, blowing obstructions to vision, and precipitation. Fog and low stratus restrict navigation by visual reference more often than all other weather phenomena.