Nine of the 12 fatalities reported during last week's severe weather outbreak occurred in Wayne and Ozark counties.

In some extreme cases, thunderstorms can spawn a derecho, a long-lived windstorm with gusts over 100 mph, strong enough to cause widespread destruction. If a severe thunderstorm warning mentions damaging winds or a derecho, take cover immediately—just as you would for a tornado.

The "scale of devastation" in Missouri is "staggering," Gov. Mike Kehoe (R) said Sunday. One of the 17 tornadoes that struck that state left a "debris field" where a house stood previously, Butler County coroner Jim Akers said. "The floor was upside down. We were walking on walls."

Ameren is reporting thousands of customers without power in the aftermath of severe storms that hit the St. Louis region.As of 9:45 p.m. on Monday, Ameren Missouri reported 8,858 outages statewide:Jefferson County: 2,