Valley Breeze: An upward flow of air which developes during the day in the mountains.
Vapor Pressure: The pressure exerted by the water vapor in the atmosphere.
Vapor Pressure:The amount of moisture the atmosphere is holding at a given temperature.
The portion of air pressure exerted by the water vapor content of air. Expressed in
"Grams" of water vapor per "Kilogram" of dry air also called: "Mixing Ratio".
"Example" Vapor Pressure = 10
----- .50 X 100 = Relative Humidity = 50%
Saturation Vapor Pressure = 20
Vapor Trail: Same as contrail.
Veering: A clock-wise movement in wind direction. Example: East to Southeast.
Vertical Wind Shear: Wind direction change & speed with height.
VFR Weather: Ceiling greater than3,000 ft. and visibility greater than 5 miles.
VFR: In flying: Visual Flight Rules
VHF: Very High Frequency. 30 to 300 MHz radio frequency.
Virga: Precipitation in the form of rain, snow, sleet etc, falling from clouds and
evaporating before reaching the ground.
Visibility: The greatist distance at which objects can be seen with the naked eye.
Visibility: Prevailing: Visibility throughout half the horizon circle.
Visibility: Sector: Visibility within a centern area of the horizon circle.
Visibility: Slant: The distance a pilot can see the landing aids (LIGHTS) on a runway.
This estimate is configured by using a transmissometer located near the landing portion of the runway, runway light intensity, and computers.
Visibility: Surface: Visibility observed from a definite location.
Visibility: Tower: Visibility observed from a control tower.
Visibility: Virtical: The Distance one can see up to clouds or through an obscuration: The distance from which a pilot can see the ground through clouds or an obscuration.
VLF: Very Low Frequency. 3 to 3 khz radio frequency.
Volcanic Ash: Very fine particles of powered rock produced by a "Volcanic Explosion"
Volcanic Explosion: A violent explosion of a volacano produced by subterranean heated rock.
VOR: A VHF Omnidirectional Range Navigation System.
VORTAC: A very high frequency omnidirectional range station and/or tactical air navigation.
Vortex: A spinning in the atmosphere.
1. Vorticity: Meaning to spin or rotate.
2. Vorticity: Positive Rising air. Negative Sinking air.
3. Vorticity: Positive: Cyclonic. Negative: Anti-cyclonic.
4. Vorticity: Absolute: Combined movements of the earth and the atmosphere.
5. Vorticity: Negative: Anticyclonic: Downward: Diversion.
6. Vorticity: Positice: Cyclonic: Upward: Conversion.
7. Vorticity: Relative: Air movement relative to the Earth's rotation.
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