Answer A is Incorrect, Try Again


Answer B is Incorrect, Try Again


Answer C is Incorrect, Try Again


Answer B is correct. AC 61-23 Pilotís Handbook of Aeronautical Knowledge, Page 3-4
Density Altitude - This altitude is pressure altitude corrected for nonstandard temperature variations. When conditions are standard, pressure altitude and density altitude are the same. Consequently, if the temperature is above standard, the density altitude will be higher than pressure altitude.

Answer B is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 9-20
First, compute the pressure altitude conversion. Find the "Altimeter Setting" and read across to the "Pressure Altitude Conversion Factor" and add it to or subtract it from the airport elevation. Next, locate the outside air temperature on the scale along the bottom of the graph. Draw a line up to the pressure altitude line. Draw a line straight across to the far left side of the graph and read the approximate density altitude.

Answer A is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 9-20
First, compute the pressure altitude conversion. Find the "Altimeter Setting" and read across to the "Pressure Altitude Conversion Factor" and add it to or subtract it from the airport elevation. Next, locate the outside air temperature on the scale along the bottom of the graph. Draw a line up to the pressure altitude line. Draw a line straight across to the far left side of the graph and read the approximate density altitude.

Answer B is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 9-20
First, compute the pressure altitude conversion. Find the "Altimeter Setting" and read across to the "Pressure Altitude Conversion Factor" and add it to or subtract it from the airport elevation. Next, locate the outside air temperature on the scale along the bottom of the graph. Draw a line up to the pressure altitude line. Draw a line straight across to the far left side of the graph and read the approximate density altitude.

Answer A is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 9-20
First, compute the pressure altitude conversion. Find the "Altimeter Setting" and read across to the "Pressure Altitude Conversion Factor" and add it to or subtract it from the airport elevation. Next, locate the outside air temperature on the scale along the bottom of the graph. Draw a line up to the pressure altitude line. Draw a line straight across to the far left side of the graph and read the approximate density altitude.

Answer C is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 9-20
First, compute the pressure altitude conversion. Find the "Altimeter Setting" and read across to the "Pressure Altitude Conversion Factor" and add it to or subtract it from the airport elevation. Next, locate the outside air temperature on the scale along the bottom of the graph. Draw a line up to the pressure altitude line. Draw a line straight across to the far left side of the graph and read the approximate density altitude.

Answer A is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 10-4
Standard sea level pressure is defined as 29.92 in. Hg. at 59oF(15oC).

Answer C is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 10-9
Wind shear is a sudden, drastic change in windspeed and/or direction over a very small area. ..While wind shear can occur at any altitude, low-level wind shear is especially hazardous due to the proximity of an aircraft to the ground.

Answer C is correct. AC 00-6, Aviation Weather, Page 64
Stable Air: Stratiform clouds and fog; Continuous precipitation; Smooth air; Fair to poor visibility in haze and smoke.

Answer C is correct. Multiple Sources,
Weather involves movement of air and changes of state of water. Air movement ultimately can be traced to heating from the sun. Changes of state of water (evaporation, condensation, melting, freezing, and sublimation) all involve adding or releasing heat.

Answer A is correct. AC 00-6 Aviation Weather, Page 23
Differences in temperature create differences in pressure. These pressure differences drive a complex system of winds in a never ending attempt to reach equilibrium.

Answer C is correct. AC 00-6 Aviation Weather, Page 9
An increase in temperature with altitude is defined as an inversion, i.e. lapse rate is inverted.

Answer A is correct. AC 00-6 Aviation Weather, Page 9
An inversion often develops near the ground on clear, cool nights when wind is light. The ground radiates and cools much faster than the overlying air.

Answer A is correct. AC 00-6 Aviation Weather, Page 10
A ground based inversion favors poor visibility by trapping fog, smoke, and other restrictions into low levels of the atmosphere.

Answer B is correct. AC 00-6 Aviation Weather, Page 20
On a hot day, the air becomes "thinner" or lighter, and its density where you are is equivalent to a higher altitude in the standard atmosphere - thus the term "high density altitude."

Answer C is correct. AC 00-6 Aviation Weather, Page 19
Density altitude simply is the altitude in the standard atmosphere where air density is the same as where you are.

Answer B is correct. AC 00-6 Aviation Weather, Page 30
Friction between the wind and the terrain surface slows the wind. As frictional force slows the windspeed, Coriolis force decreases. The stronger pressure gradient force turns the wind at an angle to the isobars toward lower pressure.

Answer C is correct. AC 00-6 Aviation Weather, Page 38
Dew point is the temperature to which air must be cooled to become saturated by the water vapor already present in the air.

Answer B is correct. AC 00-6 Aviation Weather, Page 38
Temperature largely determines the maximum amount of water vapor air can hold.

Answer A is correct. AC 00-6 Aviation Weather, Page 40/41
As air becomes saturated, water vapor begins to condense on the nearest available surface. Some condensation nuclei have an affinity for water and can induce condensation or sublimation even when air is almost but not completely saturated.

Answer A is correct. AC 00-6 Aviation Weather, Page 39
Evaporation, condensation, sublimation, freezing, and melting are changes of state. Evaporation is the changing of liquid water to invisible water vapor. Condensation is the reverse process. Sublimation is the changing of ice directly to water vapor, or water vapor to ice, bypassing the liquid state in each process.

Answer B is correct. AC 00-6 Aviation Weather, Page 41
Frost forms in much the same way as dew. The difference is that the dew point of surrounding air must be colder than freezing. Water vapor then sublimates directly as ice crystals or frost rather than condensing as dew.

Answer C is correct. AC 00-6 Aviation Weather, Page 43
Ice pellets always indicate freezing rain at higher altitude.

Answer C is correct. AC 00-6 Aviation Weather, Page 51
In a convective current, temperature and dew point converge at about 4.4 degrees F (2.5 degrees C) per 1,000 feet.

Answer A is correct. AC 00-6 Aviation Weather, Page 64
Unstable Air: Cumuliform clouds; Showery precipitation; Rough air (turbulence); Good visibility, except in blowing obstructions.

Answer A is correct. AC 00-6 Aviation Weather, Page 64
Unstable Air: Cumuliform clouds; Showery precipitation; Rough air (turbulence); Good visibility, except in blowing obstructions.

Answer A is correct. AC 00-6 Aviation Weather, Page 50
Since stable air resists convection, clouds in stable air form in horizontal, sheet-like layers or "strata." Thus, within a stable layer, clouds are stratiform. Adiabatic cooling may be by upslope flow; by lifting over cold, more dense air; or by converging winds.

Answer A is correct. AC 00-6 Aviation Weather, Page 52
If the temperature increases with altitude through a layer - an inversion - the layer is stable and convection is suppressed.

Answer C is correct. AC 00-6 Aviation Weather, Page 50
Unstable air favors convection. A "cumulus" cloud, meaning "heap," forms in a convective updraft and builds upward. Thus, within an unstable layer, clouds are cumuliform; and the vertical extent of the cloud depends on the depth of the unstable layer.

Answer B is correct. AC 00-6 Aviation Weather, Figure 42
A mass of air in which the temperature decreases rapidly with height favors instability; but, air tends to be stable if the temperature changes little or not at all with altitude.

Answer A is correct. AC 00-6 Aviation Weather, Page 49
Surface heating or cooling aloft can make the air more unstable; on the other hand, surface cooling or warming aloft often tips the balance toward greater stability.

Answer A is correct. AC 00-6 Aviation Weather, Page 50
Since stable air resists convection, clouds in stable air form in horizontal, sheet-like layers or "strata." Thus, within a stable layer, clouds are stratiform. Adiabatic cooling may be by upslope flow; by lifting over cold, more dense air; or by converging winds.

Answer B is correct. AC 00-6 Aviation Weather, Page 53
The prefix nimbo or the suffix nimbus means raincloud.

Answer B is correct. AC 00-6 Aviation Weather, Page 53
For identification purposes, you need be concerned only with the more basic cloud types, which are divided into four "families." The families are: high clouds, middle clouds, low clouds, and clouds with extensive vertical development.

Answer C is correct. AC 00-6 Aviation Weather, Figure 56
Towering cumulus signifies a relatively deep layer of unstable air. Showers can result from these clouds. Very strong turbulence; some clear icing above the freezing level.

Answer B is correct. AC 00-6 Aviation Weather, Figure 57
Cumulonimbus are the ultimate manifestation of instability. Nearly the entire spectrum of flying hazards are contained in these clouds including violent turbulence.

Answer A is correct. AC 00-6 Aviation Weather, Page 65
Temperature is one of the most easily recognized discontinuities across a front.

Answer A is correct. AC 00-6 Aviation Weather, Page 65
Wind always changes across a front. Wind discontinuity may be in direction, in speed, or in both.

Answer C is correct. AC 00-6 Aviation Weather, Page 64
Stable Air: Stratiform clouds and fog; Continuous precipitation; Smooth air; Fair to poor visibility in haze and smoke.

Answer C is correct. AC 00-6 Aviation Weather, Page 64
The zone between two different air masses is a frontal zone or front.

Answer B is correct. AC 00-6 Aviation Weather, Page 86
Wind shear may be associated with either a wind shift or a wind speed gradient at any level in the atmosphere. Three conditions are of special interest - (1) wind shear with a low-level temperature inversion, (2) wind shear in a frontal zone, and (3) clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Answer C is correct. AC 00-6 Aviation Weather, Page 88
You can be relatively certain of a shear zone in the inversion if you know the wind at 2,000 to 4,000 feet is 25 knots or more. Allow a margin of airspeed above normal climb or approach speed to alleviate danger of a stall in the event of turbulence or sudden change in wind velocity.

Answer C is correct. AC 00-6 Aviation Weather, Page 92
Two conditions are necessary for structural icing in flight: (1) the aircraft must be flying through visible water such as rain or cloud droplets, and (2) the temperature at the point where the moisture strikes the aircraft must be 0 degrees C or colder. Aerodynamic cooling can lower temperature of an airfoil to 0 degrees C even though the ambient temperature is a few degrees warmer.

Answer C is correct. AC 00-6 Aviation Weather, Page 100
A condition favorable for rapid accumulation of clear icing is freezing rain below a frontal surface. Rain forms above the frontal surface at temperatures warmer than freezing. Subsequently, it falls through air at temperatures below freezing and becomes supercooled. The supercooled drops freeze on impact with an aircraft surface.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
Precipitation beginning to fall from the cloud base is your signal that a downdraft has developed and a cell has entered the mature stage.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
For a thunderstorm to form, the air must have (1) sufficient water vapor, (2) an unstable lapse rate, and (3) an initial boost (lifting) to start the storm process in motion.

Answer A is correct. AC 00-6 Aviation Weather, Page 111
For a thunderstorm to form, the air must have (1) sufficient water vapor, (2) an unstable lapse rate, and (3) an initial boost (lifting) to start the storm process in motion.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
Downdrafts characterize the dissipating stage of the thunderstorm cell and the storm dies rapidly.

Answer A is correct. AC 00-6 Aviation Weather, Page 111
All thunderstorm hazards reach their greatest intensity during the mature stage.

Answer A is correct. AC 00-6 Aviation Weather, Page 114
A squall line is a non-frontal, narrow band of active thunderstorms. Often it develops ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front. It often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Answer B is correct. AC 00-6 Aviation Weather, Page 114
A squall line is a non-frontal, narrow band of active thunderstorms. Often it develops ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front. It often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Answer B is correct. AC 00-6 Aviation Weather, Page 115
Outside the cloud, shear turbulence has been encountered several thousand feet above and 20 miles laterally from a severe storm. A low level turbulent area is the shear zone between the plow wind and surrounding air.

Answer C is correct. AC 00-6 Aviation Weather, Page 123
During thunderstorm penetration: Don't change power settings; maintain settings for reduced airspeed. Do maintain a constant attitude; ... Maneuvers in trying to maintain constant altitude increase stresses on the aircraft.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
The key feature of the cumulus stage is an updraft.

Answer A is correct. AC 00-6 Aviation Weather, Page 126
Conditions favorable for radiation fog are clear sky, little or no wind, and a small temperature-dew point spread (high relative humidity).

Answer C is correct. AC 00-6 Aviation Weather, Page 126
Fog is a surface based cloud composed of either water droplets or ice crystals. Small temperature-dew point spread is essential for fog to form.

Answer B is correct. AC 00-6 Aviation Weather, Page 127
Advection fog forms when moist air moves over colder ground or water. It is common along coastal areas... Wind much stronger than 15 knots lifts the fog into a layer of low stratus or stratocumulus. This fog frequently forms offshore as a result of cold water and then is carried inland by the wind.

Answer C is correct. AC 00-6 Aviation Weather, Page 127
Upslope fog 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.

Answer C is correct. AC 00-6 Aviation Weather, Page 153
Steam fog, often called "sea smoke," forms in winter when cold, dry air passes from land areas over comparatively warm ocean waters. Low level turbulence can occur and icing can become hazardous.

Answer C is correct. AC 00-6 Aviation Weather, Page 115
Outside the cloud, shear turbulence has been encountered several thousand feet above and 20 miles laterally from a severe storm. A low level turbulent area is the shear zone between the plow wind and surrounding air.

Answer A is correct. Multiple Sources,
Thunder is caused by lightning. Unless there is lightning there can be no "thunder" storm.

Answer B is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 10-13
When lifted, unsaturated air cools at a rate of 5.4oF per 1,000 feet and the dewpoint temperature decreases at a rate of 1oF per 1,000 feet. This results in a convergence of temperature and dewpoint at a rate of 4.4oF.

Answer B is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 10-6
In the Northern Hemisphere, this flow of air from areas of high to low pressure is deflected to the right: producing a clockwise circulation around an area of high pressure...also known as anti-cyclonic circulation. The opposite is true of low-pressure areas; the air flows toward a low and is deflected to create a counter-clockwise or cyclonic circulation.

Answer A is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 10-6
The Coriolis force deflects air to the right in the Northern Hemisphere, causing it to follow a curved path instead of a straight line.

Answer C is correct. FAA-H-8083-25 Pilotís Handbook of Aeronautical Knowledge, Page 10-6
High-pressure systems are generally areas of dry, stable, descending air. Good weather is typically associated with high-pressure systems for this reason. Conversely, air flows into a low-pressure area to replace rising air...bad weather is commonly associated with areas of low pressure.

Answer C is correct. AC 00-6, Aviation Weather, Page 111
For a thunderstorm to form, the air must have (1) sufficient water vapor, (2) an unstable lapse rate, and (3) an initial boost (lifting) to start the storm process in motion.

Answer A is correct. AC 00-6 Aviation Weather, Page 9
This decrease of temperature with altitude is defined as lapse rate. The average decrease of temperature - average lapse rate - in the troposphere is 2 degrees C per 1,000 feet.

Answer A is correct. Multiple Sources,
Weather involves movement of air and changes of state of water. Air movement ultimately can be traced to heating from the sun. Changes of state of water (evaporation, condensation, melting, freezing, and sublimation) all involve adding or releasing heat.

Answer A is correct. AC 00-6 Aviation Weather, Page 9
An inversion often develops near the ground on clear, cool nights when wind is light. The ground radiates and cools much faster than the overlying air.

Answer A is correct. AC 00-6 Aviation Weather, Figure 10
The Standard Atmosphere: Mean Sea Level - Pressure 29.92 in. Hg or 1013.2 millibars; Temperature 15.0oC or 59oF.

Answer B is correct. AC 00-6 Aviation Weather, Page 21
To compute density altitude, set your altimeter at 29.92 inches or 1013.2 millibars and read pressure altitude from your altimeter. Read outside air temperature and then use your flight computer to get density altitude.

Answer A is correct. AC 00-6 Aviation Weather, Page 26
The instant air begins moving, Coriolis force deflects it to the right. Soon the wind is deflected a full 90 degrees and is parallel to the isobars or contours. At this time, Coriolis force exactly balances pressure gradient force.

Answer A is correct. AC 00-6 Aviation Weather, Page 35
A low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; thus we have the general association of low pressure - bad weather.

Answer A is correct. AC 00-6 Aviation Weather, Page 25
The Coriolis force affects the paths of aircraft; missiles; flying birds; ocean currents; and, most important to the study of weather, air currents. The force deflects air to the right in the Northern Hemisphere, and to the left in the Southern hemisphere.

Answer C is correct. AC 00-6 Aviation Weather, Page 24
The closer the spacing of isobars, the stronger is the pressure gradient force. The stronger the pressure gradient force, the stronger is the wind.

Answer B is correct. AC 00-6 Aviation Weather, Page 29
As winds try to blow inward toward the center of low pressure, they are also deflected to the right. Thus, the wind around a low is counterclockwise. The low pressure and its wind system is a cyclone.

Answer C is correct. AC 00-6 Aviation Weather, Page 23
Differences in temperature create differences in pressure. These pressure differences drive a complex system of winds in a never ending attempt to reach equilibrium.

Answer B is correct. AC 00-6 Aviation Weather, Page 72
Shallow frontal surfaces tend to give extensive cloudiness with large precipitation areas. If temperature of the cold air near the surface is below freezing, precipitation falls as freezing rain or ice pellets.

Answer A is correct. AC 00-6 Aviation Weather, Page 39
Some rain may reach the ground or it may evaporate as it falls into drier air. "Virga" - streamers of precipitation trailing beneath clouds but evaporating before reaching the ground.

Answer C is correct. AC 00-6 Aviation Weather, Page 39
Evaporation, condensation, sublimation, freezing, and melting are changes of state. Evaporation is the changing of liquid water to invisible water vapor. Condensation is the reverse process. Sublimation is the changing of ice directly to water vapor, or water vapor to ice, bypassing the liquid state in each process.

Answer A is correct. AC 00-6 Aviation Weather, Page 43
Ice pellets always indicate freezing rain at higher altitude.

Answer B is correct. AC 00-6 Aviation Weather, Page 38
The difference between air temperature and dew point temperature is popularly called the "spread." As spread becomes less, relative humidity increases, and it is 100% when temperature and dew point are the same.

Answer C is correct. AC 00-6 Aviation Weather, Page 51
In a convective current, temperature and dew point converge at about 4.4 degrees F (2.5 degrees C) per 1,000 feet.

Answer C is correct. AC 00-6 Aviation Weather, Page 50
Since stable air resists convection, clouds in stable air form in horizontal, sheet-like layers or "strata." Thus, within a stable layer, clouds are stratiform. Adiabatic cooling may be by upslope flow; by lifting over cold, more dense air; or by converging winds.

Answer B is correct. AC 00-6 Aviation Weather, Page 50
Whether the air is stable or unstable within a layer largely determines cloud structure.

Answer B is correct. AC 00-6 Aviation Weather, Page 50
Whether the air is stable or unstable within a layer largely determines cloud structure.

Answer C is correct. AC 00-6 Aviation Weather, Page 111
For a thunderstorm to form, the air must have (1) sufficient water vapor, (2) an unstable lapse rate, and (3) an initial boost (lifting) to start the storm process in motion.

Answer B is correct. AC 00-6 Aviation Weather, Page 64
Stable Air: Stratiform clouds and fog; Continuous precipitation; Smooth air; Fair to poor visibility in haze and smoke.

Answer B is correct. AC 00-6 Aviation Weather, Figure 42
A mass of air in which the temperature decreases rapidly with height favors instability; but, air tends to be stable if the temperature changes little or not at all with altitude.

Answer B is correct. AC 00-6 Aviation Weather, Page 49
Surface heating or cooling aloft can make the air more unstable; on the other hand, surface cooling or warming aloft often tips the balance toward greater stability.

Answer A is correct. AC 00-6 Aviation Weather, Page 49
Surface heating or cooling aloft can make the air more unstable; on the other hand, surface cooling or warming aloft often tips the balance toward greater stability.

Answer C is correct. AC 00-6 Aviation Weather, Figure 56
Towering cumulus signifies a relatively deep layer of unstable air. Showers can result from these clouds. Very strong turbulence; some clear icing above the freezing level.

Answer B is correct. AC 00-6 Aviation Weather, Page 50
Since stable air resists convection, clouds in stable air form in horizontal, sheet-like layers or "strata." Thus, within a stable layer, clouds are stratiform. Adiabatic cooling may be by upslope flow; by lifting over cold, more dense air; or by converging winds.

Answer B is correct. AC 00-6 Aviation Weather, Page 64
Cool air moving over a warm surface is heated from below, generating instability.

Answer B is correct. AC 00-6 Aviation Weather, Page 64
Unstable Air: Cumuliform clouds; Showery precipitation; Rough air (turbulence); Good visibility, except in blowing obstructions.

Answer B is correct. AC 00-6 Aviation Weather, Figure 64
In the cold front occlusion, the coldest air is under the cold front. When it overtakes the warm front, it lifts the warm front aloft; and the cold air replaces cool air at the surface.

Answer C is correct. AC 00-6 Aviation Weather, Page 86
Wind shear may be associated with either a wind shift or a wind speed gradient at any level in the atmosphere. Three conditions are of special interest - (1) wind shear with a low-level temperature inversion, (2) wind shear in a frontal zone, and (3) clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Answer C is correct. AC 00-6 Aviation Weather, Page 86
Wind shear may be associated with either a wind shift or a wind speed gradient at any level in the atmosphere. Three conditions are of special interest - (1) wind shear with a low-level temperature inversion, (2) wind shear in a frontal zone, and (3) clear air turbulence (CAT) at high levels associated with a jet stream or strong circulation.

Answer C is correct. AC 00-6 Aviation Weather, Page 100
A condition favorable for rapid accumulation of clear icing is freezing rain below a frontal surface. Rain forms above the frontal surface at temperatures warmer than freezing. Subsequently, it falls through air at temperatures below freezing and becomes supercooled. The supercooled drops freeze on impact with an aircraft surface.

Answer B is correct. AC 00-6 Aviation Weather, Page 114
A squall line is a non-frontal, narrow band of active thunderstorms. Often it develops ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front. It often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Answer C is correct. AC 00-6 Aviation Weather, Page 115
Outside the cloud, shear turbulence has been encountered several thousand feet above and 20 miles laterally from a severe storm. A low level turbulent area is the shear zone between the plow wind and surrounding air.

Answer C is correct. AC 00-6 Aviation Weather, Page 114
A squall line is a non-frontal, narrow band of active thunderstorms. Often it develops ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front. It often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
Precipitation beginning to fall from the cloud base is your signal that a downdraft has developed and a cell has entered the mature stage.

Answer C is correct. AC 00-6 Aviation Weather, Page 115
The roll cloud is most prevalent with cold frontal or squall line thunderstorms and signifies an extremely turbulent zone.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
The key feature of the cumulus stage is an updraft.

Answer A is correct. AC 00-6 Aviation Weather, Page 111
Precipitation beginning to fall from the cloud base is your signal that a downdraft has developed and a cell has entered the mature stage.

Answer B is correct. AC 00-6 Aviation Weather, Page 115
You should anticipate possible hail with any thunderstorm, especially beneath the anvil of a large cumulonimbus.

Answer C is correct. AC 00-6 Aviation Weather, Page 115
Hail has been observed in clear air several miles from the parent thunderstorm.

Answer C is correct. AC 00-6 Aviation Weather, Page 111
Downdrafts characterize the dissipating stage of the thunderstorm cell and the storm dies rapidly.

Answer C is correct. AC 00-6 Aviation Weather, Page 127
Advection fog forms when moist air moves over colder ground or water. It is common along coastal areas... Wind much stronger than 15 knots lifts the fog into a layer of low stratus or stratocumulus. This fog frequently forms offshore as a result of cold water and then is carried inland by the wind.

Answer C is correct. AC 00-6 Aviation Weather, Page 127
Advection fog is usually more extensive and much more persistent than radiation fog. Advection fog can move in rapidly regardless of the time of day or night.

Answer B is correct. AC 00-6 Aviation Weather, Page 127
Advection fog forms when moist air moves over colder ground or water. It is common along coastal areas... Wind much stronger than 15 knots lifts the fog into a layer of low stratus or stratocumulus. This fog frequently forms offshore as a result of cold water and then is carried inland by the wind.

Answer A is correct. AC 00-6 Aviation Weather, Page 127
Advection fog forms when moist air moves over colder ground or water. It is common along coastal areas... Wind much stronger than 15 knots lifts the fog into a layer of low stratus or stratocumulus. This fog frequently forms offshore as a result of cold water and then is carried inland by the wind.

Answer C is correct. AC 00-6 Aviation Weather, Page 128
When relatively warm rain or drizzle falls through cool air, evaporation from the precipitation saturates the cool air and forms fog. It is most commonly associated with warm fronts, but can occur with slow moving cold fronts and with stationary fronts.

Answer C is correct. AC 00-6 Aviation Weather, Page 128
When relatively warm rain or drizzle falls through cool air, evaporation from the precipitation saturates the cool air and forms fog. It is most commonly associated with warm fronts, but can occur with slow moving cold fronts and with stationary fronts.

Answer B is correct. AC 00-6 Aviation Weather, Page 136
An abrupt change in temperature lapse rate characterizes the tropopause.

Answer A is correct. AC 00-6 Aviation Weather, Page 173
Cool air must sink to force warm air upward in thermals. Therefore, thermals and downdrafts coexist side by side. The net upward displacement of air must equal the net downward displacement. Fast rising thermals generally cover a small percentage of a convective area while slower downdrafts predominate over the remaining greater portion.

Answer B is correct. AC 00-6 Aviation Weather, Page 173
Cool air must sink to force warm air upward in thermals. Therefore, thermals and downdrafts coexist side by side. The net upward displacement of air must equal the net downward displacement. Fast rising thermals generally cover a small percentage of a convective area while slower downdrafts predominate over the remaining greater portion.

Answer B is correct. AC 00-6 Aviation Weather, Page 173
Cool air must sink to force warm air upward in thermals. Therefore, thermals and downdrafts coexist side by side. The net upward displacement of air must equal the net downward displacement. Fast rising thermals generally cover a small percentage of a convective area while slower downdrafts predominate over the remaining greater portion.

Answer A is correct. AC 61-23 Pilotís Handbook of Aeronautical Knowledge, Page 4-14
Locate the outside air temperature at the bottom of the chart and draw a vertical line until it intersects with the pressure altitude. From where the temperature and pressure altitude lines intersect, draw a straight line to the left to determine the density altitude.

Answer B is correct. AC 00-6 Aviation Weather, Page 2
Since most weather occurs in the troposphere and since most flying is in the troposphere and stratosphere, we restrict our discussions mostly to these two layers.

Answer B is correct. AC 00-6 Aviation Weather, Page 9
This decrease of temperature with altitude is defined as lapse rate. The average decrease of temperature - average lapse rate - in the troposphere is 2 degrees C per 1,000 feet.

Answer A is correct. AC 00-6 Aviation Weather, Page 9
An inversion often develops near the ground on clear, cool nights when wind is light. The ground radiates and cools much faster than the overlying air.

Answer A is correct. AC 00-6 Aviation Weather, Page 7
The amount of solar energy received by any region varies with time of day, with seasons, and with latitude. These differences in solar energy create temperature variations. These temperature variations create forces that drive the atmosphere in its endless motions.

Answer C is correct. AC 00-6 Aviation Weather, Page 20
At a specified indicated airspeed, your true airspeed and your groundspeed increase proportionally as density altitude becomes higher.

Answer A is correct. AC 00-6 Aviation Weather, Page 12
Within the lower few thousand feet of the troposphere, pressure decreases roughly one inch for each 1,000 feet increase in altitude.

Answer C is correct. AC 00-6 Aviation Weather, Page 29
The winds are clockwise around highs and counterclockwise around lows.

Answer B is correct. AC 00-6 Aviation Weather, Page 35
A low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; thus we have the general association of low pressure - bad weather.

Answer B is correct. AC 00-6 Aviation Weather, Page 23
Differences in temperature create differences in pressure. These pressure differences drive a complex system of winds in a never ending attempt to reach equilibrium.

Answer B is correct. AC 00-6 Aviation Weather, Page 38
The difference between air temperature and dew point temperature is popularly called the "spread." As spread becomes less, relative humidity increases, and it is 100% when temperature and dew point are the same.

Answer A is correct. AC 00-6 Aviation Weather, Page 39
Some rain may reach the ground or it may evaporate as it falls into drier air. "Virga" - streamers of precipitation trailing beneath clouds but evaporating before reaching the ground.

Answer C is correct. AC 00-6 Aviation Weather, Page 43
Ice pellets always indicate freezing rain at higher altitude.

Answer C is correct. AC 00-6 Aviation Weather, Page 51
In a convective current, temperature and dew point converge at about 4.4 degrees F (2.5 degrees C) per 1,000 feet.

Answer A is correct. AC 00-6 Aviation Weather, Figure 42
A mass of air in which the temperature decreases rapidly with height favors instability; but, air tends to be stable if the temperature changes little or not at all with altitude.

Answer C is correct. AC 00-6 Aviation Weather, Page 50
Since stable air resists convection, clouds in stable air form in horizontal, sheet-like layers or "strata." Thus, within a stable layer, clouds are stratiform. Adiabatic cooling may be by upslope flow; by lifting over cold, more dense air; or by converging winds.

Answer A is correct. AC 00-6 Aviation Weather, Figure 52
Nimbostratus is a gray or dark massive cloud layer, diffused by more or less continuous rain, snow, or ice pellets. Very little turbulence, but can pose a serious icing problem if temperatures are near or below freezing.

Answer C is correct. AC 00-6 Aviation Weather, Page 64
Unstable Air: Cumuliform clouds; Showery precipitation; Rough air (turbulence); Good visibility, except in blowing obstructions.

Answer A is correct. AC 00-6 Aviation Weather, Page 49
Surface heating or cooling aloft can make the air more unstable; on the other hand, surface cooling or warming aloft often tips the balance toward greater stability.

Answer A is correct. AC 00-6 Aviation Weather, Page 64
Cool air moving over a warm surface is heated from below, generating instability.

Answer C is correct. AC 00-6 Aviation Weather, Page 64
Unstable Air: Cumuliform clouds; Showery precipitation; Rough air (turbulence); Good visibility, except in blowing obstructions.

Answer C is correct. AC 00-6 Aviation Weather, Page 88
A temperature inversion forms near the surface on a clear night with calm or light surface wind. Wind just above the inversion may be relatively strong. A wind shear zone develops between the calm and the stronger winds above. Eddies in the shear zone cause airspeed fluctuations as an aircraft climbs or descends through the inversion.

Answer B is correct. AC 00-6 Aviation Weather, Page 88
A temperature inversion forms near the surface on a clear night with calm or light surface wind. Wind just above the inversion may be relatively strong. A wind shear zone develops between the calm and the stronger winds above. Eddies in the shear zone cause airspeed fluctuations as an aircraft climbs or descends through the inversion.

Answer A is correct. AC 00-6 Aviation Weather, Page 100
When an aircraft enters the heavy water concentrations found in cumuliform clouds, the large drops break and spread rapidly over the leading edge of the airfoil forming a film of water. If temperatures are freezing or colder, the water freezes quickly to form a solid sheet of clear ice.

Answer C is correct. AC 00-6 Aviation Weather, Page 92
Two conditions are necessary for structural icing in flight: (1) the aircraft must be flying through visible water such as rain or cloud droplets, and (2) the temperature at the point where the moisture strikes the aircraft must be 0 degrees C or colder. Aerodynamic cooling can lower temperature of an airfoil to 0 degrees C even though the ambient temperature is a few degrees warmer.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
Precipitation beginning to fall from the cloud base is your signal that a downdraft has developed and a cell has entered the mature stage.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
For a thunderstorm to form, the air must have (1) sufficient water vapor, (2) an unstable lapse rate, and (3) an initial boost (lifting) to start the storm process in motion.

Answer B is correct. AC 00-6 Aviation Weather, Page 111
The key feature of the cumulus stage is an updraft.

Answer A is correct. AC 00-6 Aviation Weather, Page 115
Hail has been observed in clear air several miles from the parent thunderstorm.

Answer B is correct. AC 00-6 Aviation Weather, Page 114
A squall line is a non-frontal, narrow band of active thunderstorms. Often it develops ahead of a cold front in moist, unstable air, but it may develop in unstable air far removed from any front. It often contains severe steady-state thunderstorms and presents the single most intense weather hazard to aircraft.

Answer B is correct. AC 00-6 Aviation Weather, Page 126
Conditions favorable for radiation fog are clear sky, little or no wind, and a small temperature-dew point spread (high relative humidity).

Answer C is correct. AC 00-6 Aviation Weather, Page 127
Advection fog is usually more extensive and much more persistent than radiation fog. Advection fog can move in rapidly regardless of the time of day or night.

Answer A is correct. AC 00-6 Aviation Weather, Page 127
Advection fog forms when moist air moves over colder ground or water. It is common along coastal areas... Wind much stronger than 15 knots lifts the fog into a layer of low stratus or stratocumulus. This fog frequently forms offshore as a result of cold water and then is carried inland by the wind.

Answer C is correct. AC 00-6 Aviation Weather, Page 126
Fog is a surface based cloud composed of either water droplets or ice crystals. Small temperature-dew point spread is essential for fog to form.

Answer C is correct. AC 00-6 Aviation Weather, Page 128
When relatively warm rain or drizzle falls through cool air, evaporation from the precipitation saturates the cool air and forms fog. It is most commonly associated with warm fronts, but can occur with slow moving cold fronts and with stationary fronts.

Answer A is correct. AC 00-6 Aviation Weather, Page 173
Cool air must sink to force warm air upward in thermals. Therefore, thermals and downdrafts coexist side by side. The net upward displacement of air must equal the net downward displacement. Fast rising thermals generally cover a small percentage of a convective area while slower downdrafts predominate over the remaining greater portion.

Answer C is correct. AIM Aeronautical Information Manual, Paragraph 7-1-24(d)(4)
An individual microburst will seldom last longer than 15 minutes from the time it strikes the ground until dissipation. The horizontal winds continue to increase during the first 5 minutes with the maximum intensity winds lasting approximately 2-4 minutes.

Answer A is correct. AIM Aeronautical Information Manual, Paragraph 7-1-24(d)(2)
The downdrafts can be as strong as 6,000 feet per minute. Horizontal winds near the surface can be as strong as 45 knots resulting in a 90 knot shear (headwind to tailwind change for a traversing aircraft) across the microburst.

Answer A is correct. AIM Aeronautical Information Manual, Paragraph 7-1-24(d)(4)
An individual microburst will seldom last longer than 15 minutes from the time it strikes the ground until dissipation. The horizontal winds continue to increase during the first 5 minutes with the maximum intensity winds lasting approximately 2-4 minutes.


© 2005 Jim D. Burch 602-942-2734 jdburch@att.net