The East Coast is experiencing the early stages of what could be a whiplash-inducing stretch of winter weather.

The storm is bringing heavy rain and fierce winds to many areas until Wednesday night, and flooding is possible in some places.

One of the key factors driving the weather is an atmospheric river, which is a long band of water vapor that can transport moisture from the tropics to more northern areas, said Derek Schroeter, a forecaster with the National Weather Service in Gray, Maine.

A massive storm system will hammer virtually the entire East Coast this Wednesday, with flash floods possible in multiple major cities.