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Extreme Winds

Damage from severe wind accounts for half of all weather damage reports in the lower 48 states and is more common than damage from tornadoes. Wind speeds can reach up to 100 mph and produce a damage path extending for hundreds of miles. These winds are often called "straight-line" winds to differentiate their damage from tornado damage. Damaging winds are classified as those exceeding 50-60 mph.
 
Since most thunderstorms produce some straight-line winds as a result of outflow generated by the thunderstorm downdraft, anyone living in thunderstorm-prone areas of the world is at risk for experiencing this phenomenon.
 

Types of Damaging Winds

Straight-line winds – Defines any thunderstorm wind that is not associated with rotation, and is used mainly to differentiate from tornadic winds.
 
Downdraft – A small-scale column of air that rapidly sinks toward the ground. A downburst is a result of a strong downdraft.
 
Downburst – A strong downdraft with horizontal dimensions larger than 4 km (2.5 mi) resulting in an outward burst of 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.
 
Microburst – 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 wind speeds 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, a temperature drop, and gusty winds out ahead of a thunderstorm. Sometimes the winds push air above them, forming a shelf cloud or detached roll cloud.
 
Derecho – A derecho is a widespread, thunderstorm wind 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. The word "derecho" is of Spanish origin and means "straight ahead." Derechos typically occur in the summer months, when complexes of thunderstorms form over the plains states. Usually these thunderstorms produce heavy rain and severe winds as they rumble across several states during the night. They are particularly dangerous because the damaging winds can last a long time and cover such a large area.
 
Bow Echo – A radar echo that is linear, but bent outward in a bow shape. Damaging straight-line winds often occur near the "crest" or the 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 ground level.
 
 

Threat definitions of damaging winds

- - from the NOAA National Severe Storms Laboratory