More than 50 million Americans throughout the Northeast are under flood watches on Monday, with a significant risk of flash flooding in some areas. Flash flood warnings have been issued for cities including New York City, Newark, New Jersey, and Arlington, Virginia -- including the Reagan National Airport -- through Monday evening.

A flood warning was in effect for all five boroughs of New York City on Monday night, while New Jersey declared a state of emergency

Storms prompted flash flood warnings across the New York City metropolitan area Monday night, with photos showing severe flooding across the city and in parts of New York state and New Jersey.