Wind Basics Hurricane Tornado Wind / Hail Thunderstorm History / U.S. Hurricane Preparation Call Center Certification

[ Wind Basics : Types of Damaging Winds ]

Straight-line Winds - a term used to define any thunderstorm wind that is not associated with rotation, and is used mainly to differentiate from tornadic winds.

Derecho - The word "derecho" is of Spanish origin and means "straight ahead". A derecho is a widespread thunderstorm wind event caused when new thunderstorms form along the leading edge of an outflow boundary (a surface boundary formed by the horizontal spreading of thunderstorm-cooled air). The thunderstorms feed on this boundary and continue to reproduce themselves. Derechos typically occur in the summer months when complexes of thunderstorms form over the plains and northern plains states. Usually these thunderstorms produce heavy rain and severe wind reports as they rumble across several states during the night. They are particularly dangerous because the damaging wind can last several hours and can cover a large swath area. Derechos typically occur along two axes. One axis extends along the "corn belt" from the upper Mississippi Valley into the Ohio Valley. The other warm season axis extends from the mid Mississippi Valley into the southern Plains. During the cool season derechos most likely occur from eastern Texas into the southeastern states. Although derechos are extremely rare west of the Great Plains, isolated derecho events have occurred in the interior portions of the western United States during the spring.

Bow Echo - A radar echo which is linear but bent outward in a bow shape. Damaging straight-line winds often occur near the "crest" or center of a bow echo. Bow echoes can be over 300km in length, last for several hours, and produce extensive swaths of wind damage at the ground.

Downdrafts - A small-scale column of air that rapidly sinks toward the ground. A downburst is a result of a strong downdraft.

Downbursts - A strong downdraft with horizontal dimensions larger than 4 km (2.5 mi) resulting in an outward burst or damaging winds on or near the ground. (Imagine the way water comes out of a faucet and hits the bottom of the sink.) Downburst winds may begin as a microburst and spread out over a wider area, sometimes producing damage similar to a strong tornado. Although usually associated with thunderstorms, downbursts can occur with showers too weak to produce thunder.

Microbursts - A small concentrated downburst that produces an outward burst of damaging winds at the surface. Microbursts are generally small (less than 4km across) and short-lived, lasting only 5-10 minutes, with maximum windspeeds up to 168 mph. There are two kinds of microbursts: wet and dry. A wet microburst is accompanied by heavy precipitation at the surface. Dry microbursts, common in places like the high plains and the intermountain west, occur with little or no precipitation reaching the ground.

Gust Front - A gust front is the leading edge of rain-cooled air that clashes with warmer thunderstorm inflow. Gust fronts are characterized by a wind shift, temperature drop, and gusty winds out ahead of a thunderstorm. Sometimes the winds push up air above them, forming a shelf cloud or detached roll cloud.

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