Weather Flashcards
Low Pressure Areas
Heated air is less dense than cool air, and therefore rises and creates low pressure areas.
- draws air into the low pressure area, and the circulation pattern is counterclockwise
High Pressure Areas
When rising air has cooled, it descends and creates areas of high pressure.
Air descends in a clockwise direction, and travels away from the center when it reaches the surface
Descending air warms and dries, good news!
Coriolis Force
Because of earth’s rotation, it deflects the moving air, so that in the latitudes of the US, the prevailing upper levels winds are westerly.
Isobars
connect areas of equal pressure on a weather map, and they define pressure patterns
when isobars are tightly packed, pressure is changing rapidly, and strong winds should be expected
Pressure Gradient force
air moves from areas of high pressure to fill in the low pressure areas
this force, combines with Coriolis force, deflects the wind so the the direction of air motion actually crosses the isobars at an angle
Change in wind direction aloft
As a general rule, winds above 2000 feet AGL come from a direction several degrees clockwise from the surface wind.
Moisture content of air
heated air can hold more moisture in invisible form than cold air
Sublimation
water changes state from solid to vapor without a liquid phase
Dew Point
the temperature at which the air becomes saturated and can contain no more moisture, without the moisture getting you wet (not invisible)
Relative Humidity
how close the air is to being saturated
Air temperature lapse while climbing
4.4 degrees F per 1000 feet
or 2 degrees C per 1000 feet
example:
If temp at the reface is 78 F, and dew point is 62 F, the difference is 16. divide by 4.4 and multiply by 1000 = 3,600 feet AGL is where to expect the cloud bases to be.
Weather Front
where air masses with different properties meet.
Warm, and Cold.
When cold and warm air meets, the cold air stays at the surface, and pushes the warm air up.
favored areas for clouds, showers, and thunderstorms
Friction slows the cold air at the surface, so that the front is quite vertical in cross section
Cold fronts can move as fast as 30 knots
Cold Front Weather
Visibility - good behind the front. Warm air and pollutants rise rapidly because warm air is less dense than cold air
Flight conditions: bumpy as thermal currents rise
Precipitation: showered in the frontal area as the warm is is forced aloft and its moisture condenses.
Cloud type: Cumulus, due to air being raised
Icing possibility: Clear ice.
Warm Front Weather
- warm front exists when a warm air mass overtakes a slow-moving Cole air mass
- the warm air is forced to rise as it moves forward.
- this slow upward movement combined with the slow forward movement characteristic of warm fronts allows the warm air to cool slowly.
- As it reaches the condensation level, stratiform clouds develop.
- Warm fronts slope upward for any miles, and weather may be extensive
You may encounter warm front clouds 50 to 100 miles from where the front is depicted on the surface analysis chart
Visibility: poor, pollutants trapped by warm air aloft
Flight conditions: Smooth, no thermal activity
Precipitation: Drizzle or continuous rain as moist air is slowly raised to the condensation level
Cloud Type: status or layered
Icing possibility: Rime ice; small water droplets freeze instantly upon contact with the airplane, form a rough, oily coating.
Occlusion
- occasionally, a fast-moving cold front will overtake a warm front and lift the warm air away from the surface
- contains the worse features of both warm and cold fronts:
turbulent, showers and/or continuous precipitation, poor visibility, and broad geographic extent of frontal weather conditions.
