Where did this come from?

It had been London-like for most of a day and a half. Low clouds. Cool temps. Occassional drizzle. Then the sun came out for the hottest part of the day, 3:00 to 6:00 pm. Then, it got Kansas-like, in a big fat hurry.

By 7:30, I had tornado warnings 15 miles to my east, 10 miles to my north, and 20 miles to my south.