Winter Weather Warnings for 12 States as Clipper System Moves Across US

Winter weather warnings are in place for 12 U.S. states as meteorologists predict an Alberta Clipper system brings snow across a swathe from Montana to South Carolina, while the Pacific Northwest continues to be pummeled by an atmospheric river storm.

The National Weather Service (NWS) has issued warnings concerning snow and strong winds for parts of Alaska, California, the Carolinas, Idaho, Maryland, Montana, Nevada, Oregon, Tennessee and the Virginias, warning of reduced visibility and snow accumulations at higher elevations.

The weather agency said in a forecast on Tuesday evening that the Alberta Clipper system was "continuing its trek across the nation," and would likely produce areas of snow from the Ohio Valley to the lower Great Lakes and Appalachian mountains into Wednesday.

While it said snow was expected to be "mostly scattered with light accumulations," the NWS said portions of the Allegheny mountains—part of the Appalachians in Maryland—would see enhanced snow, where 3-6 inches is possible in places.

In the state's Garrett County, slippery road conditions and up to two inches of snow are expected. The same is anticipated for the northern Blue Ridge mountain range, as well as in Grayson and Highland County in Virginia, and Grant and Pendleton counties in West Virginia.

Up to three inches is expected for Greenbrier County in Virginia, as well as several counties in North Carolina. Around one inch of snow will fall across Avery County in South Carolina, with wind gusts as high as 40 miles an hour.

An Alberta Clipper is a fast-moving low-pressure system that tends to move southeast across the continental U.S. from the Canadian province, usually occurring during winter and bringing snow and high winds. Another variation of the same system is called a "Saskatchewan Screamer".

The NWS said snow showers were likely to fall across the Great Lakes and northeast through Thursday with the "most noteworthy snow" occurring along the Appalachians.

Mountain areas in eastern Tennessee are anticipated to see 1-3 inches above 2,500 feet and further snow accumulation at higher elevations. In Montana, up to 14 inches could fall in some parts.

An atmospheric river system off the Pacific is expected to continue bringing rain, snow and the potential for flooding to the northwest, though the NWS said snow will retreat to above 4,000 feet by Thursday. On Friday, it had warned that a "strong" atmospheric river was anticipated to "wallop" the region from Sunday.

Atmospheric rivers are narrow channels in the atmosphere that can 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.

As much as seven inches of snow is expected across the Ruby and Humboldt mountain ranges in Nevada, with up to eight inches above 4,000 feet in the Sierra Nevada mountains in California.

Oregon's Cascades region will see snow accumulations of up to 21 inches above 3,500 feet, with rates of between five and eight inches falling every 12 hours. Between one and five inches are anticipated to fall at higher elevations in Idaho.

Several warnings have also been issued for parts of Alaska, where up to six inches of snow could fall, with wind gusts up to 50 miles an hour.

The West Coast faced a similar weather front earlier 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.