The_Doctor

32 minutes ago, Chinook said:

It is kind of interesting that there were two or more disconnected squall line events, that produced such a perfectly connected pattern of wind damage reports. This would probably fit the definition of a (couple of) derecho(es). I suppose the classic definition of derecho is contained in Johns and Hirt (1987) Not that I want to look this up and read this, but the paper citation is:

Johns, R. H., and W. D. Hirt, 1987: Derechos: widespread convectively induced windstorms. Wea. Forecasting, 2, 32-49.

Found this definition on the SPC website:

"By definition, if the swath of wind damage extends for more than 250 miles (about 400 kilometers), includes wind gusts of at least 58 mph (93 km/h) along most of its length, and also includes several, well-separated 75 mph (121 km/h) or greater gusts, then the event may be classified as a derecho. "

I think that the North Dakota and Southern Illinois storms would be considered derechos under this definition. Certainly a very active day of severe weather

A question I have is why on visible satellite loops areas far from the totality path appear to get very dark when on the ground there is not much (but still noticeable) dimming.