What is a derecho ?

A derecho is a violent storm system that can produce widespread wind damage across a large area. It’s usually associated with a rapidly moving band of showers and thunderstorms. The strong to violent winds are typically associated ahead of the main system as the outflow from the storms becomes more concentrated. Wind damage is typically directed into one direction and can create widespread damage along a relatively straight path. These windstorms typically form in the late spring and summer and typically affect states east of the Rocky Mountains.

A derecho has a very specific definition in meteorology, and must include the follow criteria to be classified as a derecho:

1) There must be a concentrated area of convectively induced wind damage/gusts greater than 50 knots, or 60 miles per hour.

2) The area must have a major axis length of 400 kilometers, or 248.5 miles.

3) Wind reports should showa continuous and non random pattern of occurrence. For instance, a swath of storms should consistently produce wind reports as the system moves to the east or south east.

4) In the storm reported areas, at least three reports, separated by 64 km or more, should include wind gusts greater than 64 knots, or 74 mph.

5) Derechos are typically continuous and can sustain itself for hours. With that said, no more than three hours can elapse between successive wind damage events.

If a derecho is moving into your area, go inside and stay away from windows and find a room away from trees that could fall and crash into your house.