ON THIS DATE IN 2012: One of the most destructive, fast-moving severe thunderstorm complexes in U.S. history carving an 800-mile path of destruction from Indiana all the way to the Atlantic coast in less than 12 hours.
A small cluster of storms in Iowa rapidly evolved into a massive, forward-propagating bow echo, known as a derecho. It caused 22 fatalities and left more than 4 million customers without power—making it the largest non-hurricane power outage on record at the time.
Compounding the disaster, a brutal, prolonged heatwave gripped the region during the subsequent week-long grid restoration.
I really wish we better understood the boundary layer processes leading up to tornadogenesis. This storm went from nothing to tornado-capable in 30 minutes and had a hook echo as soon as it was detectable on reflectivity. No prior mesocyclone, no nudgers, nothin.