Feb 11, 2009 11:35 AM

Straight-Line Winds

When we think of the worst storm damage, we often think of tornadoes, which are essentially rotating winds. However, high winds could cause damage whether they are rotating or going straight. In fact, straight-line winds are responsible for most thunderstorm wind damage and can exceed 100 mph.

Damage from severe thunderstorm winds is much more common then damage from tornadoes. The damage path from these winds could extend for hundreds of miles and create widespread damage. In fact, it accounts for half of all severe weather reports in the continental United States. In order for the winds to be categorized as severe, the winds must meet or exceed 58 mph.

Straight-line winds go by many names. They include downbursts, outflow, and convective wind gusts. These winds are an area of rapidly descending air beneath a thunderstorm.

Air moves up and down vertically in a thunderstorm. Updrafts (air moving up) tend to take warmer air aloft, while downdrafts (air moving down) tend to bring cooler air to the warmer surface. The stronger these updrafts and downdrafts are, the easier it is for the formation of strong straight-line winds.

In addition, the presence of dry air above the surface helps their development. Rain will evaporate as it falls into drier air. This will cause the surrounding air to cool, become more dense, and therefore sink. The colder the air (in comparison to the surrounding air), the faster it will sink. This sinking air forms the winds that will hit the ground. When they reach the surface, they have nowhere to go but out. Therefore, they'll spread along the ground. This is why cooler air is often noticed at the surface.

If the storm system as a whole is moving quickly, this will add to the strength of the straight-line winds. The speed of the downdraft will combine with the forward motion of the storm to create strong to severe winds out ahead of the storm.

Anyone living in an area that receives thunderstorms, such as Kentucky, is at risk for experiencing downbursts. These downbursts can cause equivalent damage to a tornado. Sometimes the only difference is the direction of the damage. Straight-line wind damage will push the debris in the same direction as the wind is blowing, while tornado damage will scatter the debris in different directions due to the rotating winds of a tornado. People often won't take severe thunderstorm warnings as seriously as tornado warnings, but both could be dangerous and should be taken seriously.

A few steps could be taken to reduce the damage from straight-line winds. Keep objects secure that could be blown around by the wind and keep trees groomed. In addition, make sure you have a safe place to go when severe thunderstorm and tornado warnings are issued.


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