Winter Storm Warnings Issued for Four States as Atmospheric River Continues

Winter storm warnings remain in place for four states, following a "multi-day" storm that brought snow and rain to many parts of the western U.S. at the weekend, with further precipitation expected to come later this week.

The National Weather Service (NWS)-issued warnings will continue for parts of Maine, New Hampshire, Wyoming and Alaska following the snowstorms. A fifth, for areas of Vermont, expired at 10 a.m. ET on Monday.

The NWS said in its latest forecast that an ongoing snowstorm affecting New England would "slowly subside" on Monday, but that an atmospheric river will "soak" the Pacific Northwest and continue to bring heavy rainfall through the middle of the week.

On Friday, it warned that a "strong" atmospheric river was anticipated to "wallop" the region from Sunday, with flood watches issued for western Washington state and Oregon.

Atmospheric rivers are narrow channels in the atmosphere that are able to carry a large amount of moisture with them. A strong river is able to carry as much as 15 times the amount of water flowing through the mouth of the Mississippi River, according to the National Oceanic and Atmospheric Administration.

The weekend's precipitation saw snowfall of up to several feet in high-elevation areas across the northwest. The NWS fears that fresh rainfall could increase snowmelt, exacerbating the potential for flooding.

In Washington and Oregon, rain could reach in excess of three inches in places, while moderate rainfall could extend east of the Cascades mountain range.

"A broad stream of anomalous atmospheric moisture content extending from just north of Hawaii is forecast to move inland into western Washington and Oregon by tonight along a frontal boundary, which is also connected to a very strong low pressure system entering the Gulf of Alaska," the NWS predicts. "The subtropical connection will lead to a very mild system with high snow levels."

It will not be the first to hit the West Coast this year: In January, California was battered by a series of deadly storms that brought severe flooding. Thousands of homes were left without power and many people were evacuated.

Winter storm warnings continue to be in effect for central and western Maine and northern New Hampshire—where an additional two inches is expected to accumulate, bringing the storm total to 8-14 inches—as well as the Sierra Madre and Snowy ranges in Wyoming, where up to five feet of snow may fall.

Southern Alaska will remain under a storm warning until noon local time tomorrow, with 5-12 inches of snow expected to make roads in the region treacherous.

While the snow may subside over New England, the NWS expects another system to move over the Dakotas later on Monday, bringing scattered snow showers to the surrounding states and through towards West Virginia on Wednesday.