Downdraft - A sudden descent of cool or cold air to the ground, usually with precipitation, and associated with a thunderstorm or shower.  Contrast with an updraft.

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 such as a sudden excessive rainfall, the failure of a dam, or the thaw of an ice jam.

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 floodwaters.

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

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 when the temperature and the dew point of the air have become the same, or nearly the same, and sufficient condensation nuclei are present.

Microburst - A severe localized wind blasting down from a thunderstorm. It covers an area less than 2.5 miles (4 kilometers) in diameter and is of short duration, usually less than 5 minutes.  See downburst.

Thunderstorm - Produced by a cumulonimbus cloud, it is a microscale event of relatively short duration characterized by thunder, lightning, gusty surface winds, turbulence, hail, icing, precipitation, moderate to extreme up and downdrafts, and under the most severe conditions, tornadoes.

Tornado - A violently rotating column of air in contract with and extending between a connective cloud and the surface of the earth. It is the most destructive of all storm-scale atmospheric phenomena.  They can occur anywhere in the world given the right conditions, but are most frequent in the United States in an area bounded by the Rockies on the west and the Appalachians in the East.

Turbulence - The irregular and instantaneous motions of air that is made up of a number of small of eddies that travel in the general air current.  Atmospheric turbulence is caused by random fluctuations in the wind flow. It can be caused by thermal or connective currents, differences in terrain and wind speed, along a frontal zone, or variation in temperature and pressure.

Twister - A slang term used in the United States for a tornado.

Warning - A forecast issued when severe weather has developed, is already occurring and reported, or is detected on radar.  Warnings state a particular hazard or imminent danger, such as tornadoes, severe thunderstorms, flash and river floods, winter storms, heavy snows, etc.

Watch - A forecast issued well in advance of a severe weather event to alert the public of the possibility of a particular hazard, such s tornadoes, severe thunderstorms, flash and river floods, winter storms or heavy snows.

Waterspout - A small, weak tornado, that is not formed by a storm-scale rotation. It is generally weaker than a super-cell tornado and is not associated with a wall cloud or mesocyclone. It may be observed beneath cumulonimbus or towering cumulus clouds.

Wind - Air that flows in reaction to the earth's surface; generally horizontally.  There are four areas of wind that are measured:  direction, speed, character (gusts and squalls), and shifts. Wind vanes and anemometers measure surface winds, while upper level winds are detected through pilot balloons, or aircraft reports.

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