On Thursday, the severe storms will be in the eastern Great Lakes, parts of inland Northeast and into Ohio Valley, including Cincinnati, Pittsburgh and Syracuse.
The biggest threat Thursday will be damaging winds and large hail. In areas where the storms persist the longest, heavy rain could produce flash flooding.
Heat and fire danger
The Southern heat wave continues from Texas to Alabama, where seven states are under a heat advisory.
The heat index is forecast to reach nearly 110 degrees in some areas, making it dangerous just to be outdoors.
Several wildfires and brush fires broke out Wednesday from California to Washington as dry, gusty and hot winds swept over the area.
Six Western states -- from California to Montana -- are under heat and fire alerts Thursday as more gusty winds and dry conditions are expected.