Derecho Frequency Across the U.S.A.

Damage from 2020 Iowa Derecho Damage
Photo: The Weather Network

We are in peak derecho season.

Derechoes are defined by the Glossary of Meteorology as:

A widespread convectively induced straight-line windstorm.

Specifically, the term is defined as any family of particularly damaging downburst clusters produced by a mesoscale convective system. Such systems have sustained bow echoes with book-end vortices and/or rear-inflow jets and can generate considerable damage from straight-line winds. Damage must be incurred either continuously or intermittently over a swath of at least 650 km (~400 mi) and a width of approximately 100 km (~60 mi) or more.

The significance of derechoes is they can generate winds of 100 mph or stronger and bring widespread crop damage, power outages, tree damage, and structural damage. 

While they can occur in just about any month, late May, June, and early July seem to have the most occurrences with an elevated threat through summer. The National Weather Service released a new map of derecho frequency:

As far as known, Hawaii and Alaska do not have derechoes. 

When you hear a derecho is forecast, it is time to prepare for wind damage. When we forecast derechoes on this blog, I will add preparation suggestions.