Science behind Saturday’s storm threat: Potential bow echoes, derecho bring damaging winds

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The WHNT News 19 Weather Authority is worried about widespread power outages and wind damage on Saturday due to the potential for a squall line to push through the Tennessee Valley.

The region has experienced squall lines before, but what makes this one so powerful?

Bow echoes bring damaging straight-line winds

When a squall line begins to surge, strong winds behind the line push ahead, producing wind gusts ahead of the line. On radar, the appearance of the line begins to take the shape of a bow, which is why it's called a "bow echo".

According to the National Weather Service, 46% of bow echoes begin as unorganized thunderstorms, whereas 30% form from squall lines, and 24% from supercell thunderstorms.

If the bow echo (or series of bow echoes) travels greater than 250 mileswith widespread wind gusts of 58 mph or greater, then the bow echo is classified as a derecho.

Bow echoes and derechos can be just as damaging as a tornado

For Saturday's storms, we are anticipating a line of damaging winds in excess of 30 to 50 mph. This is on par with tropical storm force winds.

But what happens if those winds were to hit your house or mobile home? What should motorists driving large vehicles, like a tractor trailer, expect?

According to the National Weather Service, these kinds of winds can damage roof shingles and the siding buildings, as well as knock down large swaths of trees and power lines. For this reason, it's important to have additional sources of information in the event that the power goes out -- these types of storms can leave thousands of people in the dark.

If you plan on traveling, drive carefully and be prepared to pull off the side of the road. Winds in excess of 60 mph can knock tractor trailers on their side.

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