Derecho or Squall Line: The Devil is in The Details

Sumant Joshi helps to clean up rubble at the East End United Methodist Church after it was heavily damaged by storms Tuesday, March 3, 2020, in Nashville, Tenn. Joshi is a resident in the area and volunteered to help clean up. Tornadoes ripped across Tennessee early Tuesday, shredding buildings and killing multiple people. (AP Photo/Mark Humphrey)

WOAY-TV (Oak Hill, WV): The word derecho has garnered attention recently, but what is it and how far in advance can be it forecast?

Historically, the term derecho was used to describe a thunderstorm structure in which rapid development of new cells along the leading edge maintained its intensity and produced wind gusts of at least 58 mph along the course of its track. There also must be several 75 mph wind gusts contained within a derecho. By definition, a derecho must produce extensive damage for at least 400 miles and be 60 miles in width.

The meteorological community has been in disagreement on the definition of a derecho, since 2016. That is….other private organizations and meteorologists have been defining a derecho as any cluster of storms that produces any degree of wind damage (not necessarily extensive) over a course of 400 miles.

The Storm Prediction Center is in route to redefining the term, but it’s going to take time. One preliminary definition that may be considered is any storm complex that produces 400 miles of high wind reports and damage. However, thunderstorms along late fall, winter and early spring cold fronts can easily satisfy the distance requirement for gusts and damage and the term derecho would be diluted to the point of no urgency from the public.

For now, if you see a forecast for a derecho a week in advance, take it with a grain of salt. Beware, though, that wind damage can still be done in a squall line ahead of a heat wave busting front. The difference….a squall line would not produce mammoth damage we saw on June 29, 2012. Your house could be spared in a squall line, but chances are you would have cleanup to do if a derecho moved over your property.

Sponsored Content