Storms damaged these properties in Owasso, Okla., on Wednesday as a tornado ripped through the area. Weather officials warn of a potential "tornado outbreak" in the region. Mike Simons - Tulsa World via the associated press

By NAZANEEN GHAFFAR, JUDSON JONES AND AMY GRAFF | THE NEW YORK TIMES

Multiple extremely strong tornadoes will most likely tear through parts of the central United States on Wednesday ahead of days of potentially once-in-a-lifetime flooding hitting the same region of the Midwest and South, forecasters said.

National Weather Service offices warned of the potential for a "tornado outbreak" across a region that stretches from Texas to Michigan, with special risk alerts in place for the Memphis, Tennessee, area, home to 1.3 million people. The storm system generating these tornadoes is expected to stall by Thursday, prompting the government forecasters to issue their highest alert for flooding over this same area as more than 1 foot of rain may fall over the next five days.

Forecasters issued a "particularly dangerous situation" tornado watch for portions of seven states: Arkansas, Tennessee, Illinois, Indiana, Missouri, Kentucky and Mississippi.

The strong language of the "particularly dangerous situation" designation is used by the weather service when forecasters want to grab attention; it only gets used in rare events, mainly when strong and violent tornadoes are possible but also in other extremely critical events such as wildfires and floods.

Intense storms in this area Wednesday afternoon and evening are expected over a relatively broad regional area, with multiple rounds of severe storms possible in some areas. The governors of Kentucky and Arkansas preemptively declared states of emergency Wednesday.

The threat for tornadoes will intensify Wednesday afternoon into the evening.

Memphis is the epicenter for where the worst of both the tornado and excessive rainfall threat is expected this week.

A broad risk of tornadoes will exist from North Texas northeastward to the southern Great Lakes, with large populations of people at risk of tornadoes in Detroit; Milwaukee; Cleveland; Chicago; Dallas; Indianapolis; St. Louis; Little Rock, Arkansas; Louisville, Kentucky; Columbus, Ohio; and Evansville, Indiana.

The rain threat shouldn't be ignored. "This is not your average flood risk," forecasters with the weather service in Memphis warned Wednesday morning.

Meteorologists said the system would not move quickly, allowing heavy rains to persist from Wednesday through the weekend. The relentless rain may lead to "significant and potentially historic" rainfall totals of 10 to 15 inches. This could create what forecasters called a "generational flooding" event, particularly in a region stretching from northeast Arkansas through western Tennessee, western Kentucky and into southern Indiana.

This storm system originated on the West Coast on Monday, where it brought heavy snow to the Sierra Nevada, which straddles California and Nevada. By Tuesday it had moved into the Plains, triggering severe thunderstorms.But its most widespread and severe threat is expected Wednesday and Wednesday night, across a region stretching from Illinois, Indiana and Ohio to Arkansas, Louisiana and Texas.

The Storm Prediction Center has issued a high risk - a Level 5 out of 5 on its scale - for these areas, cautioning that "widespread" thunderstorms could produce destructive winds, large hail and significant long-track tornadoes.

These severe storms could be particularly intense, and long-lasting severe storms at this high of a level are typically experienced only once or twice in a lifetime. This higher level of risk means forecasters with experience predicting severe storms believe widespread storms are expected to occur near or at this location.