Quiz: Weather Theory 1

Answer (C) is correct. (FAA-H-8083-25B Chap 12) Frost does not change the basic aerodynamic shape of the wing, but the roughness of its surface spoils the smooth flow of air, thus causing an increase in drag and an early airflow separation over the wing, resulting in a loss of lift.

Answer (A) is correct. (FAA-H-8083-25B Chap 12) Frost that is not removed from the surface of an airplane prior to takeoff may make it difficult to get the airplane airborne at normal takeoff speed. The frost disrupts the airflow over the wing, which increases drag.

Answer (B) is correct. (AC 00-6B Chap 3) Frost forms when both the collecting surface is below the dew point of the adjacent air and the dew point is below freezing. Frost is the deposition of water vapor to ice crystals.

Answer (A) is correct. (FAA-H-8083-25B Chap 12) Frost does not change the basic aerodynamic shape of the wing, but the roughness of its surface spoils the smooth flow of air, thus causing an increase in drag and an early airflow separation over the wing, resulting in a loss of lift.

Answer (C) is correct. (AC 00-6B Chap 16) Advection fog forms when moist air moves over colder ground or water. It is most common in coastal areas. Upslope fog forms when wind blows moist air upward over rising terrain and the air cools below its dew point. Both advection fog and upslope fog require wind to move air masses.

Answer (A) is correct. (AC 00-6B Chap 16) Radiation fog is shallow fog of which ground fog is one form. It occurs under conditions of clear skies, little or no wind, and a small temperature/dew point spread. The fog forms almost exclusively at night or near dawn as a result of terrestrial radiation cooling the ground and the ground cooling the air on contact with it.

Answer (B) is correct. (AC 00-6B Chap 16) Advection fog forms when moist air moves over colder ground or water. It is most common in coastal areas.

Answer (C) is correct. (AC 00-6B Chap 16) Steam fog forms in winter when cold, dry air passes from land areas over comparatively warm ocean waters and is composed entirely of water droplets that often freeze quickly. Low-level turbulence can occur, and icing can become hazardous.

Answer (A) is correct. (AC 00-6B Chap 3) As water vapor condenses, it becomes visible as clouds, fog, or dew.

Answer (C) is correct. (AC 00-6B Chap 14, 18) Rain falling through colder air may freeze during its descent, falling as ice pellets. Ice pellets always indicate freezing rain at a higher altitude.

Answer (C) is correct. (AC 00-6B Chap 18) Freezing rain usually causes the highest accumulation rate of structural icing because of the nature of the supercooled water striking the airplane.

Answer (C) is correct. (AC 00-6B Chap 18) Two conditions are necessary for structural icing while in flight. First, the airplane must be flying through visible moisture, such as rain or cloud droplets. Second, the temperature at the point where the moisture strikes the airplane must be freezing or below.

Answer (B) is correct. (AC 00-24C, AIM Para 7-1-26) Pilots should anticipate possible hail with any thunderstorm but especially beneath the anvil of a large cumulonimbus.

Answer (B) is correct. (FAA-H-8083-25B Chap 12) During the mature stage of a thunderstorm, precipitation descends through the cloud and drags the adjacent air downward, creating a strong downdraft. The downdraft spreads out along the surface, well in advance of the parent thunderstorm cell, as a mass of cool, gusty air. Adverse winds always are found within thunderstorms and often many miles from the precipitation area. Crosswinds, gusts, and variable winds (i.e., sudden wind shifts) can lead to a crash during takeoffs, approaches, and landings. Therefore, the best decision would be to delay departure from the departure airport until the thunderstorm has dissipated at the arrival airport.

Answer (B) is correct. (AC 00-6B Chap 19) The mature stage of a thunderstorm begins when rain begins falling. This means that the downdrafts are occurring sufficiently to carry water all the way through the thunderstorm.

Answer (A) is correct. (AC 00-6B Chap 19) A thunderstorm, by definition, has lightning, because lightning causes the thunder.

Answer (A) is correct. (AC 00-6B Chap 19) A squall line is a nonfrontal, narrow band of active thunderstorms. It often contains severe, steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Answer (B) is correct. (AC 00-6B Chap 19) The mature stage of a thunderstorm begins when rain begins falling. This means that the downdrafts are occurring sufficiently to carry water all the way through the thunderstorm.

Answer (B) is correct. (AC 00-6B Chap 19) The cumulus stage of a thunderstorm has continuous updrafts that build the storm. The water droplets are carried up until they become too heavy. Once they begin falling and creating downdrafts, the storm changes from the cumulus to the mature stage.

Answer (A) is correct. (AC 00-6B Chap 19) Thunderstorms reach their greatest intensity during the mature stage, where updrafts and downdrafts cause a high level of wind shear.

Answer (B) is correct. (AC 00-6B Chap 19) Thunderstorms have three life cycles: cumulus, mature, and dissipating. It is in the dissipating stage that the storm is characterized by downdrafts as the storm rains itself out.

Answer (A) is correct. (AC 00-6B Chap 19) Thunderstorms form when there is sufficient water vapor, an unstable lapse rate, and an initial upward boost (lifting) to start the storm process.

Answer (B) is correct. (AC 00-6B Chap 19) A nonfrontal, narrow band of active thunderstorms that often develops ahead of a cold front is known as a squall line.

Answer (B) is correct. (AC 00-6B Chap 19) The most hazardous atmospheric phenomenon near thunderstorms is wind shear turbulence.

Answer (C) is correct. (AC 00-24C) Attempting to hold altitude and airspeed in severe turbulence can lead to overstressing the airplane. Rather, you should set power to what normally will maintain VA and simply attempt to maintain a level flight attitude.

Answer (C) is correct. (AC 00-6B Chap 17) When unstable air is lifted, it usually results in considerable vertical development and associated turbulence, i.e., convective activity.

Answer (A) is correct. (AC 00-6B Chap 11) Moist, stable air flowing upslope can be expected to produce stratus type clouds as the air cools adiabatically as it moves up sloping terrain.

Answer (A) is correct. (AC 00-6B) Cumulus clouds are formed in a convective updraft, build upward, and are associated with turbulence.

Answer (C) is correct. (FAA-H-8083-25B Chap 12) 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 ft., and dew point decreases about 1°F/1,000 ft. In a convective current, temperature and dew point converge at about 4.4°F/1,000 ft. Thus, if the temperature and dew point are 70°F and 48°F, respectively, at 1,000 ft. MSL, there would be a 22°F spread that, divided by the lapse rate of 4.4, is approximately 5,000 ft. AGL, or 6,000 ft. MSL (5,000 + 1,000).

Answer (C) is correct. (AC 00-6B Chap 13) Towering cumulus clouds are an early stage of cumulonimbus clouds, or thunderstorms, that are based on convective turbulence, i.e., an unstable lapse rate.

Answer (B) is correct. (FAA-H-8083-25B Chap 12) 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.

Answer (B) is correct. (AC 00-6B Chap 13) The greatest turbulence occurs in cumulonimbus clouds, which are thunderstorm clouds.

Answer (B) is correct. (AC 00-6B Chap 19) Unstable, moist air, in addition to a lifting action, i.e., convective activity, is needed to form cumulonimbus clouds.

Answer (B) is correct. (AC 00-6B Chap 13) The suffix “nimbus” or the prefix “nimbo” means a rain cloud.

Answer (B) is correct. (FAA-H-8083-25B Chap 12) The four families of clouds are high clouds, middle clouds, low clouds, and clouds with extensive vertical development. Thus, they are based upon their height range.

Answer (B) is correct. (AC 00-45H Chap 4.1) An isobar connects areas of similar barometric pressure. On a surface analysis chart, isobars are used to depict the sea-level pressure pattern; they are depicted with a series of solid black lines surrounding the defined pressure area. The interval between isobars is typically 4 mb, based on a standard pressure gradient.

Answer (A) is correct. (AC 00-6B Chap 10) Of the many changes that take place across a front, the most easily recognized is the change in temperature. When flying through a front, you will notice a significant change in temperature, especially at low altitudes.

Answer (A) is correct. (AC 00-6B Chap 10) The definition of a front is the zone of transition between two air masses of different air pressure or density, e.g., the area separating high and low pressure systems. Due to the difference in changes in pressure systems, there will be a change in wind.

Answer (C) is correct. (AC 00-6B Chap 10) A front is a surface, interface, or transition zone of discontinuity between two adjacent air masses of different densities. It is the boundary between two different air masses.

Answer (A) is correct. (AC 00-6B) At night, heating is absent, but terrestrial radiation continues cooling the earth’s surface. Cooling continues until shortly after sunrise, when incoming solar radiation once again exceeds outgoing terrestrial radiation. Minimum surface air temperature usually occurs shortly after sunrise.

Answer (A) is correct. (FAA-H-8083-25B Chap 12) Normally, as air rises and expands in the atmosphere, the temperature decreases. However, when the temperature of the air rises with altitude, this indicates that a temperature inversion exists.

Answer (A) is correct. (AC 00-6B Chap 21) Beneath temperature inversions, there is usually smooth air because there is little vertical movement due to the inversion. There is also poor visibility due to fog, haze, and low clouds (when there is high relative humidity).

Answer (C) is correct. (AC 00-6B Chap 17) By definition, a temperature inversion is a situation in which the temperature increases as altitude increases. The normal situation is that the temperature decreases as altitude increases.

Answer (A) is correct. (AC 00-6B Chap 16) An inversion often develops near the ground on clear, cool nights when wind is light. The ground loses heat and cools the air near the ground while the temperature a few hundred feet above changes very little. Thus, temperature increases in height, which is an inversion.

Answer (A) is correct. (AC 00-6B Chap 2) A temperature inversion is associated with an increase in temperature with height, a reversal of normal decrease in temperature with height. Thus, any warm air rises to where it is the same temperature and forms a stable layer of air.

Answer (A) is correct. (AC 00-6B Chap 3) Evaporation is the process of converting a liquid to water vapor, and sublimation is the process of converting ice to water vapor.

Answer (B) is correct. (AC 00-6B Chap 3) Air temperature largely determines how much water vapor can be held by the air. Warm air can hold more water vapor than cool air.

Answer (C) is correct. (AC 00-6B Chap 3) Dew point is the temperature to which air must be cooled to become saturated or have 100% humidity.

Answer (C) is correct. (AC 00-6B Chap 16) The difference between the air temperature and dew point is the temperature/dew point spread. As the temperature/dew point spread decreases, fog or low clouds tend to develop.

Answer (C) is correct. (FAA-H-8083-25B Chap 12) Every physical process of weather is accompanied by, or is the result of, a heat exchange. A heat differential (difference between the temperatures of two air masses) causes a differential in pressure, which in turn causes movement of air. Heat exchanges occur constantly, e.g., melting, cooling, updrafts, downdrafts, wind, etc.

Answer (B) is correct. (AC 00-6B Chap 17) Wind shear is the abrupt rate of change of wind velocity (direction and/or speed) per unit of distance and is normally expressed as vertical or horizontal wind shear. Hazardous wind shear may be expected in areas of low-level temperature inversion, frontal zones, and clear air turbulence.

Answer (C) is correct. (AC 00-6B Chap 17) When taking off or landing in calm wind under clear skies within a few hours before or after sunset, prepare for a temperature inversion near the ground. You can be relatively certain of a shear zone in the inversion if you know the wind is 25 kt. or more at 2,000 to 4,000 feet. Allow a margin of airspeed above normal climb or approach speed to alleviate the danger of stall in the event of turbulence or sudden change in wind velocity.

Answer (C) is correct. (AC 00-6B Chap 17) Wind shear is the eddies in between two wind currents of differing velocities, direction, or both. Wind shear may be associated with either a wind shift or a wind speed gradient at any level in the atmosphere.

Answer (A) is correct. (AC 00-6B Chap 17) Always anticipate possible mountain wave turbulence when the air is stable and winds of 40 kt. or greater blow across a mountain or ridge.

Answer (B) is correct. (AC 00-6B Chap 17) Lens-shaped clouds, which indicate crests of standing mountain waves, are called standing lenticular clouds. They form in the updraft and dissipate in the downdraft so that they do not move as the wind blows through them.

Answer (C) is correct. (AC 00-6B Chap 17) Lenticular clouds are lens-shaped and indicate the crests of standing mountain waves. They form in the updraft and dissipate in the downdraft, so they do not move as the wind blows through them. Lenticular clouds may contain winds of 50 kt. or more and are extremely dangerous.

Answer (B) is correct. (AC 00-6B Chap 7) 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.

Answer (C) is correct. (AC 00-6B) Winds across mountains cause mountain waves that are associated with severe turbulence, strong vertical currents, and icing. The extent of the turbulence is relative to the height of the ground, speed of the wind, and instability of the atmosphere. With adequate moisture, lenticular clouds will form at the top of each wave.

Answer (B) is correct. (FAA-H-8083-25B Chap 12) The stability of the atmosphere depends on its ability to resist vertical motion. As air temperature and air moisture increase, the density of the air decreases, causing it to rise. This creates an unstable atmosphere in which small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity.

Answer (A) is correct. (AC 00-6B Chap 12) When air is warmed from below, even though cooling adiabatically, it remains warmer than the surrounding air. The colder, more dense surrounding air forces the warmer air upward, and an unstable condition develops.

Answer (C) is correct. (FAA-H-8083-25B Chap 12) Atmospheric stability influences weather by affecting the vertical motion of air. Stable air suppresses vertical motion, but unstable air enhances it. Clouds formed in stable air will be shallow and layered, e.g., stratus clouds. Clouds formed in unstable air will have more height and be of the cumulus or cumulonimbus type. Precipitation from stratus clouds tends to be over large areas and lasts for long periods. Precipitation from cumulus clouds tends to be more intense and lasts for short periods.

Answer (B) is correct. (AC 00-6B Chap 12) 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.

Answer (A) is correct. (FAA-H-8083-25B Chap 12) Characteristics of an unstable air mass include cumuliform clouds, showery precipitation, turbulence, and good visibility, except in blowing obstructions.

Answer (C) is correct. (AC 00-6B Chap 10) Steady precipitation preceding a front is usually an indication of a warm front, which results from warm air being cooled from the bottom by colder air. This results in stratiform clouds with little or no turbulence.

Answer (C) is correct. (AC 00-6B Chap 12) Characteristics of a stable air mass include stratiform clouds and fog, continuous precipitation, smooth air, and fair to poor visibility in haze and smoke.

Answer (A) is correct. (FAA-H-8083-25B Chap 12) Characteristics of an unstable air mass include cumuliform clouds, showery precipitation, turbulence, and good visibility, except in blowing obstructions.

Answer (A) is correct. (AC 00-6B Chap 10) Characteristics of a stable air mass include stratiform clouds, continuous precipitation, smooth air, and fair to poor visibility in haze and smoke.

Answer (C) is correct. (AC 00-6B Chap 9) Sea breezes are caused by cool and more dense air moving inland off the water. Once over the warmer land, the air heats up and rises. Thus the cooler, more dense air from the sea forces the warmer air up. Currents push the hot air over the water where it cools and descends, starting the cycle over again. This process is caused by land heating faster than water.

Answer (C) is correct. (AC 00-6B Chap 4) Thermals are updrafts in small-scale convective currents. Convective currents are caused by uneven heating of the Earth’s surface. Solar heating is the means of heating the Earth’s surface.

Answer (A) is correct. (FAA-H-8083-25B Chap 12) Unequal heating of the Earth’s surface causes differences in air pressure, which is reflected in differences in altimeter settings between weather reporting points.