A well-organized and long-lived complex of storms produced widespread severe wind damage across Iowa, northern Illinois, and northern Indiana during the day on Monday, August 10. Much of this severe wind was significant (75+ mph winds) resulting in many downed trees, several topped over semi trucks, and many communities had at least some minor structural damage.
Listen here to a recap of the event with KTIC’s Chad Moyer and NE Extension Ag Climatologist Al Dutcher:
Preliminary numbers from August 10 as of 6 a.m. on August 11:
Over 600 reports of severe wind speeds (58+ mph) or wind damage from the Nebraska/Iowa border, across Iowa, northern Illinois and northern Indiana.
This complex of storms was known as a derecho.
– A derecho 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.
– These are primarily classified as straight-line winds rather than tornadic.
– Even so, wind speeds in a derecho can exceed 100 mph which is equivalent to that of an EF1 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.
– 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.