National Weather Service reporting 11 tornadoes in Northern Illinois 9 of them in Chicago area from Monday’s violent weather.
Fast facts from the National Weather Service on deracho:
- 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.
- Northern Illinois and northern Indiana have long been known as a corridor of enhanced derecho activity, as shown in this graphic from a published paper by Guastini & Bosart (2016) titled “Analysis of a Progressive Derecho Climatology and Associated Formation Environments”.