What are straight-line winds?

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What are straight-line winds?
uprooted tree surrounded by green grass
Photo of uprooted tree (caused by straight-line winds) by Ron Amundson

These are ground-level winds that come from a thunderstorm but do not have rotation. If these winds travel above 57 miles per hour, then the storm is classified as a severe thunderstorm. Storms with severe straight-line winds can also produce hail and tornadoes.

Thunderstorms also have vertical air movements. Upward air motions, or updrafts, supply warm moist air to the storm and help to form the precipitation.

Downdrafts carry air from high in the atmosphere toward the ground. Since wind is nearly always much faster at high elevations, the downdrafts carry air with very high momentum that creates straight-line winds. Downdrafts also carry liquid water, and when they hit dry air, such as below a cloud, the drops evaporate, cooling the downdraft, which makes it denser and accelerates the descent. You can sometimes feel this blast of cool air just before the rain starts.

The lack of rotation in straight-line winds allows meteorologists to differentiate their damage from that due to rotating winds. Tornadoes scatter objects all over because they rotate so quickly.

Straight-line winds can blow 60 mph or faster, fast enough to flatten trees and buildings, causing injury or death, but the damage shows their straight-line path.

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.