First A ‘Derecho,’ Then A ‘Wake Low’ — How Back-To-Back Tennessee Storms May Have Been Connected

We’re learning new weather terms this week as Middle Tennessee was hit with another night of high winds, knocking out power to an additional 15,000 Nashville Electric Service customers.

This time it was a rare “wake low,” which followed an even more unusual “derecho” storm system the night before.

“They could have fed off of one another,” says meteorologist Scott Unger with the National Weather Service. “It would only make sense with the fact that we haven’t seen a derecho in so long. It’s been so long since we’ve seen a wake low. Then to have them back to back, within 24 hours of one another, you would think meteorologically, there would be a correlation between the two.”

A derecho, which is a Spanish word for “straight,” is a line of storms that can take on a life of their own and cause hurricane-force winds. They become a derecho because of how long they stay together. Sunday’s line of storms that blasted 70 mile-an-hour gusts through Middle Tennessee had assembled more than 600 miles to the west, in Kansas.

Wicked view of the storms as they rolled into Orlinda,TN earlier today.
Video: Jennifer Goostree.@WSMV #tnwx pic.twitter.com/l6KNK7RivC

— Cody Murphy 🌎 (@CodyMurphyWx) May 3, 2020

The wake low is less intense but equally mysterious.

The winds are caused not by the leading edge of a thunderstorm, but by low pressure that builds behind the front. And meteorologists say they’re impossible to predict and only detectable once they’re occurring.

The Capital Weather Gang at the Washington Post has a good explanation here.

Winds were gusting at 50 miles an hour or so. Trees can typically withstand that kind of beating, but not necessarily after surviving a derecho, the day before.

“It probably helped to finish off a few limbs out there,” Unger says.

There have been no reported injuries from the wake low, only more downed power lines. NES says they’re repairing primary lines and substations first, which could still leave some customers without power for days to come.

“A lot of people have called me asking when their power will be on and complained there hadn’t been any people in their neighborhoods,” CEO Decosta Jenkins said Tuesday morning at a press briefing. “But once we got the substation up, then they had power immediately. So that’s what we’re going to be focused on.”