Past Iowa Derechos

Derecho Facts

• A derecho (pronounced duh-REY-cho) produces a swath of particularly damaging thunderstorm winds (specifically, wind gusts of at least 58 mph along most of its length with several well-separated 75 mph or greater gusts) over an area at least 250 miles long.
   
• Wind speeds in a derecho can exceed 100 mph, which is equivalent to that of an EF-1 tornado, but over a vastly larger area than a tornado would impact.
   
• Tornadoes can also be embedded within derechos and produce concentrated areas of even more intense damage.
   
• Progressive derechos develop in an environment with very warm and moist air at the surface, colder air aloft, and moderate to strong winds at upper levels of the atmosphere. Serial derechos are caused by strong low pressure and associated strong low level winds with a squall line containing embedded bow echoes. More information about progressive and serial derechos can be found on the Storm Prediction Center's derechos page.
   
• The term was originated by Dr. Gustavus Hinrichs of the University of Iowa, first appearing in the American Meteorological Journal in 1888; he coined the term to distinguish straight-line winds from the damage caused by tornadoes (the word "derecho" comes from the Spanish term meaning "direct" or "straight ahead").

Derecho FAQs

The December 15, 2021 derecho was the first derecho in December anywhere in the United States since known records. Compared to the August 10, 2020 derecho, the impacts were not as severe in large part due to the lack of vegetation on trees. In addition, this derecho was a "serial derecho", which is characterized by a strong, migratory low pressure with strong low level winds and a squall line, or line of storms, with multiple embedded bow echoes. In contrast, a progressive derecho like the August 2020 derecho is characterized by a short line of storms with the damaging winds driven by the thunderstorm's cold pool. More information about progressive and serial derechos can be found on the Storm Prediction Center's derechos page.

While not as common with this derecho, the August 2020 derecho was often compared to an inland hurricane or hurricanes in general. While this does help people relate to the type of wind damage, this is where the comparisons between derechos and hurricanes end.

Here are a few of the key distinctions between derechos and hurricanes.

• ​A derecho lifespan typically lasts from several hours up to a day and a half, but usually no longer. Hurricanes can maintain themselves for days or even weeks as long as they can remain over warm ocean waters.
   
• The damaging winds from a derecho typically last less than a half an hour at a given location whereas a hurricane's wind speeds can last hours at a given location.
   
• Derechos have a forward motion that tends to be quite rapid and is usually 50 mph or higher. Hurricanes on the other hand typically move around 15 to 20 mph or less.
   
• Derechos can occur over land and/or water and maintain their intensity. However, once a hurricane leaves the warm ocean waters, which is the energy that feeds these systems, and move over land they quickly weaken.

Finally, while the damage from a derecho can look like tornado damage, a key distinction between a derecho and a tornado is the widespread damage swath. A tornado's width is generally less than a mile with the widest tornado width around 2.5 miles. A derecho on the other hand produces damage over a much larger width of many miles.