Severe storms to morph into big flooding threat across Midwest By (0) Meteorologists say travel through some larger cities like St. Louis could be severely slowed as a result of rain and thunderstorms that will begin to arrive Tuesday. File Photo by Bill Greenblatt/UPI | License Photo April 26 -- What will begin as an eruption of severe thunderstorms across the southern Plains late Tuesday could turn into a dangerous flash flooding situation as slow-moving downpours unload half a foot of rain or more across the south-central United States. The typically swift west-to-east progression of storm systems across the nation will be slowed down significantly this week thanks to a broad area of high pressure building in the East, which will contribute to summerlike warmth from Chicago to New York City.