Chapter 7

48) At approximately what altitude above the surface would the pilot expect the base of cumuliform clouds if the surface air temperature is 82°F and the dewpoint is 38°F?

10,000 feet AGL (The height of cumuliform cloud bases can be estimated using surface temperature/dew point spread. Unsaturated air in a convective current cools at about 5.4°F/1,000 feet, and dew point decreases about 1°F/1,000 feet. In a convective current, temperature and dew point converge at about 4.4°F/1,000 feet. Thus, if the temperature/dew point spread is 44°F (82°F - 38°F), divide 44 by 4.4 to obtain 10,000 feet AGL.)

32) A pilot can expect a wind-shear zone in a temperature inversion whenever the wind speed at 2,000 to 4,000 feet above the surface is at least

25 Knots

49) What is the approximate base of the cumulus clouds if the surface air temperature at 1,000 feet MSL is 70°F and the dewpoint is 48°F?

6,000 feet MSL (The height of cumuliform cloud bases can be estimated using surface temperature/dew point spread. Unsaturated air in a convective current cools at about 5.4°F/1,000 feet, and dew point decreases about 1°F/1,000 feet. In a convective current, temperature and dew point converge at about 4.4°F/1,000 feet. Thus, if the temperature and dew point are 70°F and 48°F, respectively, at 1,000 feet MSL, there would be a 22°F spread that, divided by the lapse rate of 4.4, is approximately 5,000 feet AGL, or 6,000 feet MSL (5,000 + 1,000).

63) What feature is associated with a temperature inversion?

A stable layer of air

60) What are the characteristics of an unstable atmosphere?

A warm, humid air mass

58) What measurement can be used to determine the stability of the atmosphere?

Actual lapse rate (Atmospheric stability is determined by vertical movements of air. Warm air rises when the air above is cooler. The actual lapse rate, which is the decrease of temperature with altitude, is therefore a measure of stability.)

42) What types of fog depend upon wind in order to exist?

Advection fog and upslope fog

40) In which situation is advection fog most likely to form?

An air mass moving inland from the coast in winter.

31) Where does wind shear occur?

At all altitudes, in all directions

53) If an unstable air mass is forced upward, what type clouds can be expected?

Clouds with considerable vertical development and associated turbulence

57) What are characteristics of a moist, unstable air mass?

Cumuliform clouds and showery precipitation

37) What are the processes by which moisture is added to unsaturated air?

Evaporation and sublimation (Evaporation is the process of converting a liquid to water vapor, and sublimation is the process of converting ice to water vapor.)

34) If the temperature/dewpoint spread is small and decreasing, and the temperature is 62°F, what type weather is most likely to develop?

Fog or low clouds

22) In which environment is aircraft structural ice most likely to have the highest accumulation rate?

Freezing rain

26) How does frost affect the lifting surfaces of an airplane on takeoff?

Frost may prevent the airplane from becoming airborne at normal takeoff speed

25) Why is frost considered hazardous to flight?

Frost spoils the smooth flow of air over the wings, thereby decreasing lifting capability

24) How will frost on the wings of an airplane affect takeoff performance?

Frost will disrupt the smooth flow of air over the wing, adversely affecting its lifting capability

55) A stable air mass is most likely to have which characteristic?

Poor surface visibility

66) Which weather conditions should be expected beneath a low-level temperature inversion layer when the relative humidity is high?

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

39) Low-level turbulence can occur and icing can become hazardous in which type of fog?

Steam fog

51) What is a characteristic of stable air?

Stratiform clouds

56) Steady precipitation preceding a front is an indication of

Stratiform clouds with little or no turbulence

27) Which conditions result in the formation of frost?

The temperature of the collecting surface is at or below the dewpoint of the adjacent air and the dewpoint is below freezing

35) What is meant by the term "dewpoint"?

The temperature to which air must be cooled to become saturated

47) What cloud types would indicate convective turbulence?

Towering cumulus clouds

54) What are characteristics of unstable air?

Turbulence and good surface visibility

2) What causes variations in altimeter settings between weather reporting points?

Unequal heating of the earths surface. (Unequal heating of the Earth's surface causes differences in air pressure, which is reflected in differences in altimeter settings between weather reporting points.)

41) What situation is most conducive (likely) to the formation of radiation fog?

Warm, moist air over low, flatland areas on clear, calm nights

59) What would decrease the stability of an air mass?

Warming form below

28) An almond or lens-shaped cloud which appears stationary, but which may contain winds of 50 knots or more, is referred to as

a lenticular cloud

44) The suffix "nimbus," used in naming clouds, means

a rain cloud

30) Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow

across a mountain ridge, and the air is stable

36) The amount of water vapor which air can hold depends on the

air temperature

65) When there is a temperature inversion, you would expect to experience

an increase in temperature as altitude increases.

61) Clouds with extensive vertical development over mountainous terrain are a sign of

an unstable air mass

62) The stability of an air mass can usually be determined by

cloud types and the type of precipitation

5) Convective circulation patterns associated with sea breezes are caused by

cool, dense air moving inland from over the water.

46) What clouds have the greatest turbulence?

cumulonimbus

3) The wind at 5,000 feet AGL is southwesterly while the surface wind is southerly. This difference in direction is primarily due to

friction between the wind and the surface. (Winds aloft at 5,000 ft. are largely affected by Coriolis force, which deflects wind to the right, in the Northern Hemisphere. But at the surface, the winds will be more southerly (they were southwesterly aloft) because Coriolis force has less effect at the surface where the wind speed is slower. The wind speed is slower at the surface due to the friction between the wind and the surface.)

1) Every physical process of weather is accompanied by, or is the result of, a

heat exchange

43) Clouds are divided into four families according to their

height range

33) When may hazardous wind shear be expected?

in areas of low-level temperature inversion, frontal zones, and clear air turbulence

23) The presence of ice pellets at the surface is evidence that there

is a temperature inversion with freezing rain at a higher altitude

67) An increase in temperature with an altitude increase

is indication of an inversion

68) Temperature and radiation variations over land with a clear sky typically lead to

minimum temperature occurring after sunrise

50) Cumulus clouds often indicate

possible turbulence

52) When warm, moist, stable air flows upslope, it

produces stratus type clouds

29) Crests of standing mountain waves may be marked by stationary, lens-shaped clouds known as

standing lenticular clouds

64) The most frequent type of ground or surface-based temperature inversion is that which is produced by

terrestrial radiation on a clear, relatively still night

45) The conditions necessary for the formation of cumulonimbus clouds are a lifting action and

unstable, moist air

21) One in-flight condition necessary for structural icing to form is

visible moisture

38) Clouds, fog, or dew will always form when

water vapor condenses