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3.1 Definitions and Acronyms

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METAR – Aviation Routine Weather Report – An Observation of current surfaced weather reported in a standard international format (METARs are issued regularly but a METAR (SPECI) can be issued anytime between routine METARs).

TAF – Terminal Aerodrome Forecast – A Concise Statement of the expected meteorological conditions at an airport during a specified period (Typically a 24hour period). TAF’s consists of the same weather codes as METARs. Amended TAFs are issued when the current TAF no longer adequately describes the current or expected weather. A TAF is a report established for the 5 Statute Mile Radius around an airport (generally larger airports), are updated 4 times a day, and valid for 24 or 30 hours. Update times for TAFS are at 0000Z, 0600Z, 1200Z, and 1800Z.

Ceiling – Lowest layer of clouds reported as being broken or overcast, or the vertical visibility into an obstruction like fog or haze

Visibility- the greatest horizontal distance at which prominent objects can be viewed with the naked eye. Reported in METAR or other aviation weather reports.

Dew – When the temperature of the ground and objects on the surface cause the temperature of the surrounding air to drop below the dew point it causes moisture to the air to deposit itself on the ground, buildings, and other objects.

Temperature / Dewpoint Relationship: Dewpoint – given in degrees, it is the temperature at which the air can hold no more moisture. When the temperature of the air is reduced to the dew point, the air is completely saturated and moisture begins to condense out of the air in the form of fog, dew frost, clouds, rain, or snow.

Frost – When the temperature of the ground and objects on the surface causes the temperature of the surrounding air to drop below freezing. It causes ice to develop on the ground, buildings, and other objects.

Squall-Line – Narrow band of active thunderstorms that often develop ahead of a cold front. (a SQUALL-LINE is referred to as the most intense hazard to an aircraft.)