The storms that moved through Friday night were part of a large, widespread wind storm called a "derecho" (pronounced "deh-RAY-cho"). This one may go down in the record books for causing the most damage.
WHAT IS A DERECHO?
Derechos start as a long line of storms that eventually take on bowing characteristics. (SEE GRAPHIC LEFT). On radar, the storm looks like an arch, with the strongest wind out ahead of the arch's point.
In Friday's case, the Derecho moved along the outer edge of high pressure, also responsible for the extended period of extreme heat.
WHEN DID IT FORM?
The derecho event started out as a cluster of storms, developing in Illinois around Noon on Friday. Travelling at 65mph, it made it to southwest Virginia in less than 9 hours.
Unless you watched the Noon/5/6 or followed the weather closely online and on mobile, you had no idea it was "on the radar." It developed that fast.