Midwestern governors declared states of emergency as severe weather and heavy rain affected parts of the region Friday.

The National Weather Service on Friday said flooding would affect parts of the Mississippi and Missouri valleys through Monday as a cold front that could end up affecting as many as 74 million Americans moved from the Rocky Mountains toward the East Coast.

Earlier this week the storm became what forecasters describe as a bombogenesis, or a bomb cyclone, where a front drops 24 millibars, or units of atmospheric pressure, in less than 24 hours.

The system was bringing with it not only 2 to 3 inches of rain but temperatures warm enough in some areas to melt snow and ice, which is contributing to flooding, officials and forecasters said. The front will reach the Mid-Atlantic on Sunday and is likely to produce rain there, too, according to the weather service.

Emergencies have been declared in parts of the Midwest because of flooding set off in by part by rapid snowmelt, officials said Friday.

Wisconsin Gov. Tony Evers said his state was under an emergency…