Science / Weather Glossary

Few: The amount of sky cover for a cloud layer between 1/8th and 2/8ths, based on the summation layer amount for that layer.

Filling: Used in describing the history of a low pressure system or an area of cyclonic circulation, it means an increase in the central pressure of the system. Although it usually describes the acti . . . View Full Definition

Firewhirl: A tornado-like rotating column of fire and smoke created by intense heat from a forest fire or volcanic eruption.

First Gust: Another name for the initial wind surge observed at the surface as the result of downdrafts forming the leading edge or gust front of a thunderstorm.

Flanking Line: A line of attached cumulus or towering cumulus clouds of descending height, appearing as stair steps (usually on the southwest side) of the most active part of a supercell.

Flash Flood: A flood that rises and falls quite rapidly with little or no advance warning, usually as the result of intense rainfall over a relatively small area. Flash floods can be caused by situations . . . View Full Definition

Flood: High water flow or an overflow of rivers or streams from their natural or artificial banks, inundating adjacent low lying areas.

Flood Plain: Level land that may be submerged by flood waters.

Flood Stage: The level of a river or stream where overflow onto surrounding areas can occur.

Foehn: A warm dry wind on the lee side of a mountain range, whose temperature is increased as the wind descends down the slope. It is created when air flows downhill from a high elevation, raising . . . View Full Definition

Fog: A visible aggregate of minute water droplets suspended in the atmosphere at or near the surface of the earth, reducing horizontal visibility to less than 5/8 statute miles. It is created whe . . . View Full Definition

Fog Bank: A fairly well-defined mass of fog observed in the distance. Most commonly seen at sea, over a lake, or along coastal areas.

Fogbow: A whitish semicircular arc seen opposite the sun in fog. The outer margin has a reddish tinge, its inner margin has a bluish tinge, and the middle of the band is white. An additional bow wit . . . View Full Definition

Forecast: A statement of expected future occurrences. Weather forecasting includes the use of objective models based on certain atmospheric parameters, along with the skill and experience of a meteorologist.

Fractus: The elements of cumulus and stratus clouds that appear in irregular fragments, as if they had been shred or torn. Never appears in cirrus clouds. Also known as scud.

Freezing Drizzle: Drizzle, falling as a liquid, but freezing on impact with the colder ground or other exposed surfaces. It is reported as 'FZDZ' in an observation and on the METAR.

Freezing Fog: Used to describe the phenomena when fog is present and the air temperature is below 0°C. It is reported as 'FZFG' in an observation and on the METAR.

Freezing Point: The process of changing a liquid to a solid. The temperature at which a liquid solidifies under any given set of conditions. Pure water under atmospheric pressure freezes at 0°C or 32°F. It . . . View Full Definition

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