Maps show where heavy rainfall poses flood risks across Northeast

More than 10 million people were under flood alerts across the northeastern United States on Wednesday, as a storm system that brought tornadoes to parts of the Midwest earlier in the week moves into New England.

The National Weather Service issued flood watches for large chunks of New York, Connecticut, Massachusetts, New Hampshire and Vermont that were set to remain in effect until Wednesday night or Thursday afternoon. A handful of metropolitan areas could be impacted, including New York City; Boston; Hartford, Connecticut; and Portland, Maine, forecasters said.

New York's capital city, Albany, was also at risk. Forecasters issued a flash flood warning for the capital and surrounding areas Wednesday morning, as radar showed 1 to 3 inches of rain had already fallen and flash flooding was "ongoing or expected to begin shortly." Up to 2 more inches of rain were expected by the afternoon.

In New York City, a flash flood warning for Tuesday's intense thunderstorms had expired by Wednesday morning. But city officials warned that even brief downpours on Wednesday could cause rushing water through streets and inundate basements or first-floor residences, CBS New York reported.

Flash flood risks were highest for Hartford and Springfield, Massachusetts, where forecasters said there would be a moderate chance of excessive rainfall. Between 2 and 5 inches of rain could fall in different sections of New England, potentially imperiling a handful of places already drenched by previous storms in recent days.

"Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations," the weather service's office in Boston wrote in a flood alert covering much of Connecticut and western Massachusetts. It noted that creeks and streams "may rise out of their banks," potentially triggering flooding in urban areas and others with poor drainage infrastructure. 

There were 84 flash flood reports across the eastern U.S. between Tuesday and Wednesday. Upstate New York saw the highest rainfall totals in that period, with Albany receiving more than 6 inches, which was the greatest amount.

Forecasters urged people in areas under flood watches to keep up with possible storm developments throughout the day, as some of those alerts may be upgraded from watches to warnings, reflecting a shift from possible to imminent flooding impacts.

"Those living in areas prone to flooding should be prepared to take action should flooding develop," the weather service said.