Unit 7: Study Session, Aviation Weather

What feature is associated with a temperature inversion? A) A stable layer of air. B) An unstable layer of air. C) Chinook winds on mountain slopes.

A) A stable layer of air. *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.

What are characteristics of a moist, unstable air mass? A) Cumuliform clouds and showery precipitation. B) Poor visibility and smooth air. C) Stratiform clouds and showery precipitation.

A) Cumuliform clouds and showery precipitation.

What are the processes by which moisture is added to unsaturated air? A) Evaporation and sublimation. B) Heating and condensation. C) Supersaturation and evaporation.

A) Evaporation and sublimation.

What conditions are necessary for the formation of thunderstorms? A) High humidity, lifting force, and unstable conditions. B) High humidity, high temperature, and cumulus clouds. C) Lifting force, moist air, and extensive cloud cover.

A) High humidity, lifting force, and unstable conditions.

Which weather phenomenon is always associated with a thunderstorm? A) Lightning. B) Heavy rain. C) Hail.

A) Lightning.

Which weather conditions should be expected beneath a low-level temperature inversion layer when the relative humidity is high? A) Smooth air, poor visibility, fog, haze, or low clouds. B) Light wind shear, poor visibility, haze, and light rain. C) Turbulent air, poor visibility, fog, low stratus type clouds, and showery precipitation.

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

What is a characteristic of stable air? A) Stratiform clouds. B) Unlimited visibility. C) Cumulus clouds.

A) Stratiform clouds.

What are characteristics of unstable air? A) Turbulence and good surface visibility. B) Turbulence and poor surface visibility. C) Nimbostratus clouds and good surface visibility.

A) Turbulence and good surface visibility.

What causes variations in altimeter settings between weather reporting points? A) Unequal heating of the Earth's surface. B) Variation of terrain elevation. C) Coriolis force.

A) Unequal heating of the Earth's surface.

What situation is most conducive to the formation of radiation fog? A) Warm, moist air over low, flatland areas on clear, calm nights. B) Moist, tropical air moving over cold, offshore water. C) The movement of cold air over much warmer water.

A) Warm, moist air over low, flatland areas on clear, calm nights. (Radiation fog is restricted to land because water cools little at night.)

What would decrease the stability of an air mass? A) Warming from below. B) Cooling from below. C) Decrease in water vapor.

A) Warming from below.

One of the most easily recognized discontinuities across a front is A) a change in temperature. B) an increase in cloud coverage. C) an increase in relative humidity.

A) a change in temperature.

Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow A) across a mountain ridge, and the air is stable. B) down a mountain valley, and the air is unstable. C) parallel to a mountain peak, and the air is stable.

A) across a mountain ridge, and the air is stable.

An increase in temperature with an altitude increase A) is indication of an inversion. B) denotes the beginning of the stratosphere. C) means a cold front passage.

A) is indication of an inversion.

Thunderstorms reach their greatest intensity during the A) mature stage. B) downdraft stage. C) cumulus stage.

A) mature stage.

Temperature and radiation variations over land with a clear sky typically lead to A) minimum temperature occurring after sunrise. B) outgoing terrestrial radiation peaking at noon. C) temperature reaching a maximum closer to noon than to sunset.

A) minimum temperature occurring after sunrise.

Cumulus clouds often indicate A) possible turbulence. B) a temperature inversion. C) a dry adiabatic lapse rate.

A) possible turbulence. *Cumulus clouds are formed in a convective updraft, build upward, and are associated with turbulence.

When warm, moist, stable air flows upslope, it A) produces stratus type clouds. B) causes showers and thunderstorms. C) develops convective turbulence.

A) produces stratus type clouds.

Thunderstorms which generally produce the most intense hazard to aircraft are A) squall line thunderstorms. B) steady-state thunderstorms. C) warm front thunderstorms.

A) squall line thunderstorms.

The most frequent type of ground or surface-based temperature inversion is that which is produced by A) terrestrial radiation on a clear, relatively still night. B) warm air being lifted rapidly aloft in the vicinity of mountainous terrain. C) the movement of colder air under warm air, or the movement of warm air over cold air.

A) terrestrial radiation on a clear, relatively still night. *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.

Clouds, fog, or dew will always form when A) water vapor condenses. B) water vapor is present. C) relative humidity reaches 100 percent.

A) water vapor condenses. *Even at 100% humidity, water vapor may not condense, e.g., sufficient condensation nuclei may not be present. *As water vapor condenses, it becomes visible as clouds, fog, or dew.

One weather phenomenon which will always occur when flying across a front is a change in the A) wind direction. B) type of precipitation. C) stability of the air mass.

A) wind direction.

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? A) 9,000 feet AGL. B) 10,000 feet AGL. C) 11,000 feet AGL.

B) 10,000 feet AGL.

What are the characteristics of an unstable atmosphere? A) A cool, dry air mass. B) A warm, humid air mass. C) Descending air in the northern hemisphere.

B) A warm, humid air mass.

What measurement can be used to determine the stability of the atmosphere? A) Atmospheric pressure. B) Actual lapse rate. C) Surface temperature.

B) Actual lapse rate. *The stability of the atmosphere 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.

In which situation is advection fog most likely to form? A) A warm, moist air mass on the windward side of mountains. B) An air mass moving inland from the coast in winter. C) A light breeze blowing colder air out to sea.

B) An air mass moving inland from the coast in winter. *Advection fog forms when moist air moves over colder ground or water. It is most common in coastal areas.

What feature is normally associated with the cumulus stage of a thunderstorm? A) Roll cloud. B) Continuous updraft. C) Frequent lightning.

B) Continuous updraft.

What clouds have the greatest turbulence? A) Towering cumulus. B) Cumulonimbus. C) Nimbostratus.

B) Cumulonimbus. *The greatest turbulence occurs in cumulonimbus clouds, which are thunderstorm clouds.

During the life cycle of a thunderstorm, which stage is characterized predominately by downdrafts? A) Cumulus. B) Dissipating. C) Mature.

B) Dissipating.

When may hazardous wind shear be expected? A) When stable air crosses a mountain barrier where it tends to flow in layers forming lenticular clouds. B) In areas of low-level temperature inversion, frontal zones, and clear air turbulence. C) Following frontal passage when stratocumulus clouds form indicating mechanical mixing.

B) In areas of low-level temperature inversion, frontal zones, and clear air turbulence.

Which weather phenomenon signals the beginning of the mature stage of a thunderstorm? A) The appearance of an anvil top. B) Precipitation beginning to fall. C) Maximum growth rate of the clouds.

B) Precipitation beginning to fall.

Which conditions result in the formation of frost? A) The temperature of the collecting surface is at or below freezing when small droplets of moisture fall on the surface. B) The temperature of the collecting surface is at or below the dewpoint of the adjacent air and the dewpoint is below freezing. C) The temperature of the surrounding air is at or below freezing when small drops of moisture fall on the collecting surface.

B) The temperature of the collecting surface is at or below the dewpoint of the adjacent air and the dewpoint is below freezing. *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.

If there is thunderstorm activity in the vicinity of an airport at which you plan to land, which hazardous atmospheric phenomenon might be expected on the landing approach? A) Precipitation static. B) Wind-shear turbulence. C) Steady rain.

B) Wind-shear turbulence.

You are avoiding a thunderstorm that is in your flightpath. You are over 20 miles from the cell; however, you are under the anvil of the cell. Is this a hazard? A) No, you are at a safe distance from the cell. B) Yes, hail can be discharged from the anvil. C) Yes, this is still in the area of dissipation.

B) Yes, hail can be discharged from the anvil. *When under the anvil, the hazards you are most likely to encounter are clear air turbulence and hail. Pilots should anticipate possible hail with any thunderstorm but especially beneath the anvil of a large cumulonimbus.

The suffix "nimbus," used in naming clouds, means A) a cloud with extensive vertical development. B) a rain cloud. C) a middle cloud containing ice pellets.

B) a rain cloud.

The amount of water vapor which air can hold depends on the A) dewpoint. B) air temperature. C) stability of the air.

B) air temperature. *Air temperature largely determines how much water vapor can be held by the air. Warm air can hold more water vapor than cool air.

The destination airport has one runway, 8-26, and the wind is calm. The normal approach in calm wind is a left-hand pattern to runway 8. There is no other traffic at the airport. A thunderstorm about 6 miles west is beginning its mature stage, and rain is starting to reach the ground. The pilot decides to A) depart expecting the thunderstorm to dissipate prior to arrival, then land on runway 8. B) delay departure until the thunderstorm has dissipated. C) fly an approach to runway 26 since any unexpected wind due to the storm will be westerly.

B) delay departure until the thunderstorm has dissipated. *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.

The wind at 5,000 feet AGL is southwesterly while the surface wind is southerly. This difference in direction is primarily due to A) stronger pressure gradient at higher altitudes. B) friction between the wind and the surface. C) stronger Coriolis force at the surface.

B) 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.

Clouds are divided into four families according to their A) outward shape. B) height range. C) composition.

B) height range.

A nonfrontal, narrow band of active thunderstorms that often develop ahead of a cold front is known as a A) prefrontal system. B) squall line. C) dry line.

B) squall line.

Crests of standing mountain waves may be marked by stationary, lens-shaped clouds known as A) mammatocumulus clouds. B) standing lenticular clouds. C) roll clouds.

B) standing lenticular clouds.

The mature stage of a thunderstorm begins with A) formation of the anvil top. B) the start of precipitation. C) continuous downdrafts.

B) the start of precipitation.

The conditions necessary for the formation of cumulonimbus clouds are a lifting action and A) unstable air containing an excess of condensation nuclei. B) unstable, moist air. C) either stable or unstable air.

B) unstable, moist air.

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 A) 10 knots. B) 15 knots. C) 25 knots.

C) 25 knots.

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? A) 4,000 feet MSL. B) 5,000 feet MSL. C) 6,000 feet MSL.

C) 6,000 feet MSL. (You have to add the 1,000 ft AGL) *The approximate base of the cumulus clouds is 5,000 feet AGL, not 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).

What types of fog depend upon wind in order to exist? A) Radiation fog and ice fog. B) Steam fog and ground fog. C) Advection fog and upslope fog.

C) Advection fog and upslope fog. *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.

Where does wind shear occur? A) Only at higher altitudes. B) Only at lower altitudes. C) At all altitudes, in all directions.

C) At all altitudes, in all directions.

If an unstable air mass is forced upward, what type clouds can be expected? A) Stratus clouds with little vertical development. B) Stratus clouds with considerable associated turbulence. C) Clouds with considerable vertical development and associated turbulence.

C) Clouds with considerable vertical development and associated turbulence.

If the temperature/dewpoint spread is small and decreasing, and the temperature is 62°F, what type weather is most likely to develop? A) Freezing precipitation. B) Thunderstorms. C) Fog or low clouds.

C) Fog or low clouds. *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.

In which environment is aircraft structural ice most likely to have the highest accumulation rate? A) Cumulus clouds with below freezing temperatures. B) Freezing drizzle. C) Freezing rain.

C) Freezing rain.

A stable air mass is most likely to have which characteristic? A) Showery precipitation. B) Turbulent air. C) Poor surface visibility.

C) Poor surface visibility. *Turbulent air is a characteristic of an unstable (not stable) air mass.

Low-level turbulence can occur and icing can become hazardous in which type of fog? A) Rain-induced fog. B) Upslope fog. C) Steam fog.

C) Steam fog.

What is meant by the term "dewpoint"? A) The temperature at which condensation and evaporation are equal. B) The temperature at which dew will always form. C) The temperature to which air must be cooled to become saturated.

C) The temperature to which air must be cooled to become saturated. (Not worded well.)

What cloud types would indicate convective turbulence? A) Cirrus clouds. B) Nimbostratus clouds. C) Towering cumulus clouds.

C) Towering cumulus clouds. *Towering cumulus clouds are an early stage of cumulonimbus clouds, or thunderstorms, that are based on convective turbulence, i.e., an unstable lapse rate.

An almond or lens-shaped cloud which appears stationary, but which may contain winds of 50 knots or more, is referred to as A) an inactive frontal cloud. B) a funnel cloud. C) a lenticular cloud.

C) a lenticular cloud. *Lenticular clouds are lens-shaped clouds, which 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.

When there is a temperature inversion, you would expect to experience A) clouds with extensive vertical development above an inversion aloft. B) good visibility in the lower levels of the atmosphere and poor visibility above an inversion aloft. C) an increase in temperature as altitude increases.

C) an increase in temperature as altitude increases.

Clouds with extensive vertical development over mountainous terrain are a sign of A) a dry adiabatic lapse rate. B) a stable air mass. C) an unstable air mass.

C) an unstable air mass. *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.

The stability of an air mass can usually be determined by A) the height of the tropopause. B) measuring the dry adiabatic lapse rate. C) cloud types and the type of precipitation.

C) cloud types and the type of precipitation. *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.

Convective circulation patterns associated with sea breezes are caused by A) warm, dense air moving inland from over the water. B) water absorbing and radiating heat faster than the land. C) cool, dense air moving inland from over the water.

C) cool, dense air moving inland from over the water.

The boundary between two different air masses is referred to as a A) frontolysis. B) frontogenesis. C) front.

C) front.

Every physical process of weather is accompanied by, or is the result of, a A) movement of air. B) pressure differential. C) heat exchange.

C) heat exchange.

The presence of ice pellets at the surface is evidence that there A) are thunderstorms in the area. B) has been cold frontal passage. C) is a temperature inversion with freezing rain at a higher altitude.

C) is a temperature inversion with freezing rain at a higher altitude.

The development of thermals depends upon A) a counterclockwise circulation of air. B) temperature inversions. C) solar heating.

C) solar heating. *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.

Steady precipitation preceding a front is an indication of A) stratiform clouds with moderate turbulence. B) cumuliform clouds with little or no turbulence. C) stratiform clouds with little or no turbulence.

C) stratiform clouds with little or no turbulence. *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.

One in-flight condition necessary for structural icing to form is A) small temperature/dewpoint spread. B) stratiform clouds. C) visible moisture.

C) visible moisture.