Thunderstorm Winds and Derechos
When most people think about winds associated with a thunderstorm, they think tornadoes; however, most years there are far more damage reports from thunderstorm straight line winds than from tornadoes. Straight line winds are thunderstorm winds that have no rotation, i.e. not a tornado.
Downbursts are a common cause of wind damage from a thunderstorm. They can reach over 100 mph and are caused by air being dragged down by precipitation. When the air reaches the ground, it spreads outward across the surface of the land it encounters in a straight line.
A Derecho is a very long lived and damaging thunderstorm. A storm is classified as a derecho if wind damage swath extends more than 240 miles and has wind gusts of at least 58 mph or greater along most of the length of the storm's path. For more on derechos visit the Storm Prediction Center's derecho page.