ROANOKE, Va. – After June of 2012, many of us became all-too-familiar with the weather term, “derecho.” The one on Monday that moved through parts of South Dakota, Nebraska, Iowa, and Illinois was extremely dangerous at times. It produced wind gusts of 80-100 mph in parts of Iowa and Illinois, wreaking havoc on corn fields, farms, houses, buildings, etc. in parts of each state.
More than 500 storm reports indicated wind damage as the storm traveled from parts of South Dakota and Nebraska to Iowa, Wisconsin, Illinois and Indiana. The Storm Prediction Center estimates that it traveled 770 miles in 14 hours, making for an average forward speed of 55 miles-per-hour.
Thankfully, the storm has dissipated leaving our area with no threat Tuesday.
What is a derecho?
This refers to a widespread storm that produces damaging straight-line winds. Damage must occur consistently, or intermittently along a path length of at least 400 miles and path width of at least 60 miles.
The National Weather Service in Omaha, one of the areas impacted by Monday’s storm, put out a great infographic on how this weather phenomenon forms.
The rising air that goes into a storm is tilted backward. Rain then falls on the back edge of the storm and cools the air down. That cool air then rushes forward, creating the intense wind gusts. We can see that on a smaller, more local scale in severe storms. This just so happens to be on a much larger scale.
Derechos, fortunately, happen fairly infrequently. If there’s one area where they happen the most, it’s in parts of the Upper Midwest.
These happen most often between May and July, but a few can still happen in the late summer months as we saw Monday.