Key Questions Flashcards
Changes or variations of weather patterns are caused by:
the unequal heating of the earths surface
Warmer air has as tendency to:
Rise (low pressure)
Colder air has the tendency to:
settle or descend (high pressure) and replace rising warmer air
Coriolis force
deflects wind to the right at higher altitudes as it rises (in northern hemisphere)
What causes variations in altimeter settings between weather reporting points?
Unequal heating of the earth’s surface
Development of thermals depends on:
solar heating (thermals are updrafts in convective currents dependent on solar heating)
The general circulation and wind rules in the Northern Hemisphere are as follows:
- Air circulates in a clockwise direction around a high
- Air circulates in a counterclockwise direction around a low
- The closer the isobars are together, the stronger the wind speed
- Due to surface friction (up to about 2,000ft AGL), surface winds do not exactly parallel the isobars , but move outward from the center of the high toward lower pressure
Convective circulation patterns associated with sea breezes are caused by:
cool, dense air moving inland from over the water
What is the proper airspeed to use when flying between thermals on a cross-country flight against a headwind?
The best lift/drag speed increased by one-half the estimated wind velocity.
When gliding into a headwind, maximum distance will be achieved by adding approximately one-half the estimated headwind velocity to the best L/D speed.
Standard Temperature (sea level)
59°F (15°C)
Standard Lapse Rate (Temperature)
2°C (3.5°F) per 1,000 feet
When there is a temperature inversion, you would expect to experience:
an increase in temperature as altitude increases
A ground-based inversion usually means poor visibility
Relative Humidity
relates the actual water vapor present in the air to that which could be present in the air. Temperature largely determines the max amount of water vapor air can hold. Warm air can hold more water vapor than cold air
Dew Point
The temperature to which air must be cooled to become saturated by the water already present in the air
Clouds, fog, or dew will always form when:
water vapor condenses
What are the processes by which moisture is added to unsaturated air?
Evaporation and sublimation
Ridge
elongated area of high pressure
Trough
elongated area of low pressure. All fronts lie in troughs
Cold Front
leading edge of an advancing cold air mass
Warm Front
leading edge of an advancing warm air mass. Warm fronts move about half as fast as cold fronts.
Frontal Waves and Cyclones (areas of low pressure)
usually form on slow-moving cold fronts or stationary fronts
Frontal Passage will be indicated by the following discontinuities:
- A temperature change (most easily recognizable)
- A continuous decrease in pressure followed by and increase as the front passes
- A shift in the wind direction, speed, or both
Atmospheric Stability
the resistance of the atmosphere to vertical motion. A stable atmosphere resists any upward or downward movement. An unstable atmosphere allows an upward or downward disturbance to grow into a vertical (convective current)
Cirrus Clouds
High clouds composed mainly of ice crystals - least likely to cause structural icing (since it requires water droplets)
Base of Cloud (formula, AGL)
= ((Surface Temp - Dew Point)/4.4) x 1,000
Steady precipitation preceding a front is an indication of:
stratiform clouds with little or no turbulence.
Precipitation from stratiform clouds is usually steady and there is little or no turbulence.
For a cumulonimbus cloud or thunderstorm to form, the air must have:
- Sufficient water vapor
- An unstable lapse rate
- An initial upward boost (lifting) to start the storm process in motion
The suffix “nimbus” used in naming clouds means
a rain cloud
Clouds are divided into 4 families according to their:
Height Range
High clouds, middle clouds, low clouds, and clouds with extensive vertical development
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.
Crests of standing waves may be marked by stationary, lens-shaped clouds known as standing lenticular clouds.
Crests of standing mountain waves may be marked by stationary, lens-shaped clouds known as:
standing lenticular clouds
What cloud types would indicate convective turbulence?
Towering cumulus clouds
Possible mountain wave turbulence could be anticipated when winds of 40 knots or greater blow
across a mountain ridge, and the air is stable
One of the most dangerous features of mountain waves is the turbulent areas in and
below rotor clouds.
Rotor clouds appear to remain stationary, parallel the range, and stand a few miles leeward of the mountains. Turbulence is most frequent and most severe in and below the standing rotors just beneath the wave crests at or below mountaintop levels.
Squall-Line Thunderstorms
Generally produce the most intense hazard to aircraft. These non-frontal, narrow bands of thunderstorms often develop ahead of a cold front.
Wind Shear
change in wind direction and/or speed over a very short distance in the atmosphere. This can occur at any level of the atmosphere and can be detected by the pilot as a sudden change in airspeed
Low-level (low-altitude) Wind Shear
Expected during strong temperature inversions, on all sides of a thunderstorm and directly below the cell.
A pilot can expect a wind shear zone in a temperature inversion whenever the wind speed at 2,000 ft. to 4,000 ft. above the surface is at least 25 knots. Can also be found near frontal activity because winds can be significantly different in the two air masses which meet to form the front.
Warm Front Shear
Most critical period is before the front passes.
Warm front shear may exist below 5,000 ft. for about 6 hours before surface passage of the front. Wind shear associated with a warm front is usually more extreme than that found in cold fronts.
Cold Front Shear
Shear associated with cold fronts is usually found behind the front. If the front is moving at 30 knots or more, the shear zone will be 5,000 feet above the surface 3 hours after frontal passage.
Fog
A surface-based cloud (restricting visibility) composed of either water droplets or ice crystals. Fog may form by cooling the air to its dew point or by adding moisture to the air near the ground.
A small temperature/dew point spread is essential to the formation of fog. An abundance of condensation nuclei from combustion products makes fog prevalent in industrial areas.
Radiation fog (ground fog)
formed when terrestrial radiation cools the ground, which in turn cools the air in contact with it. When the air is cooled to its dew point (or within a few degrees), fog will form. This fog will form most readily in warm, moist air over low, flatland areas on clear, calm (no wind) nights.
Advection fog (Sea fog)
formed when warm, moist air moves (wind is required) over colder ground or water (e.g., an air mass moving inland from the coast in winter).
Upslope fog
formed when moist, stable air is cooled to its dew point as it moves (wind is required) up sloping terrain. Cooling will be at the dry adiabatic lapse rate of approximately 3°C per 1,000 ft.
Precipitation (rain or drizzle)-induced fog
most commonly associated with frontal activity and is formed by relatively warm drizzle or rain falling through cooler air. Evaporation from the precipitation saturates the cool air and fog forms. This fog is especially critical because it occurs in the proximity of precipitation and other possible hazards such as icing, turbulence, and thunderstorms.
Steam Fog
forms in the winter when cold, dry air passes from land areas over comparatively warm ocean waters. Low-level turbulence can occur and icing can become hazardous in a steam fog.
Frost
ice deposits formed by sublimation on a surface when the temperature of the collecting surface is at or below the dew point of the adjacent air and the dew point is below freezing.
Which is true with respect to a high or low pressure system?
A high-pressure area or ridge is an area of descending air.
IFR Conditions
Ceiling less than 1,000 ft. and/or visibility less than 3 miles
For aviation purposes, ceiling is defined as the height above the Earth’s surface of the:
lowest broken or overcast layer or vertical visibility into an obscuration.
Pilot Weather Reports (PIREPs)(UA) Form
/OV - Location /TM - Time /FL - Altitude/Flight Level /TP - Aircraft Type /SK - Sky Cover /WX - Flight Visibility and Weather /TA - Temperature (°C) /WV - Wind /TB - Turbulence /IC - Icing /RM - Remarks
(see ASA 7 - 5 for full list of nomenclature)
Terminal Aerodrome Forecast (TAF)
Concise statement of the expected meteorological conditions at an airport during a specified period (usually 24 hours). TAFs use the same code used in the METAR weather reports.
TAFs are issued in the following format:
TYPE/LOCATION/ISSUANCE TIME/VALID TIME/FORECAST
What does “SHRA” stand for in a TAF?
Rain Showers
“SH” - Showers
“RA” - Rain
The only cloud type forecast in TAF reports is:
Cumulonimbus clouds
To best determine general forecast weather conditions covering a flight information region, the pilot should refer to:
The Graphical Forecasts for Aviation (GFA)
GFA’s are intended to provide the necessary aviation weather info to give users a complete picture of the weather that may impact flight in the continental U.S. (CONUS)
Winds and Temperatures Aloft Forecast (FB)
Displayed in a 6-digit format (DDffTT)
DD = Wind Direction
ff = Wind Velocity
TT = Temperatore (C)
Ex: “234502” = Winds 230° true north, at 45kts, 02°C
When the wind speed (ff) is between 100 and 199 knots, the wind direction (DD) portion of the code will be greater than 50. In cases such as this, you will need to subtract 50 from the coded wind direction, and add 100 to the coded wind speed in order to decipher the code.
Example: “734502” = winds 230° at 145 knots, temp 02°C
Light and variable winds or wind speeds below 5 knots are indicated by 9900, followed by the forecast temperature.
Observed Wind Aloft Chart
Shows temperature, wind direction, and speed at slected stations
Arrows with pennants and barbs indicate wind direction and speed. Each pennant is 50 knots, each barb is 10 knots, and each half barb is 5 knots. Wind direction is shown by an arrow drawn to the nearest 10 degrees with the second digit of the coded direction entered at the outer end of the arrow. Thus, a wind in the northwest quadrant with the digit 3 indicates 330 degrees, and a wind in the southwest quadrant with the digit 3 indicates 230 degrees.
When the term “light and variable” is used in reference to a Winds Aloft Forecast, the coded group and windspeed is:
When the forecast speed is less than 5 knots, the coded group is “9900” and reads “light and variable” on the Winds Aloft Forecast.
AIRMETs (WA)
contain info on weather that may be hazardous to single engine, other light aircraft, and VFR pilots. The items covered are moderate icing or turbulence, sustained winds of 30 knots or more at the surface, widespread areas of IFR conditions, and extensive mountain obscurement.
SIGMETs (WS)
advise of weather potentially hazardous to all aircraft, The items covered are severe icing, severe or extreme turbulence, and widespread sandstorms, dust storms or volcanic ash lowering visibility to less than 3 miles.
