First US winter storm of 2023 brings snow, sleet and flood threat

The first major US winter storm system of the year has dumped a frosty mix of snow, freezing rain and sleet from the Northern Plains to the Upper Great Lakes region, while posing a tornado and flood threat to a large swath of the South.

The National Weather Service (NWS) forecast 2-1/2 to 7-1/2 cm of snow would fall an hour, accompanied at times by thunder, and more than a foot would accumulate in parts of Nebraska, South Dakota and Minnesota on Tuesday.

Drifting and blowing snow from strong, gusty winds was expected to make road travel virtually impossible in some areas, while snow fog, mist and freezing rain created treacherous driving conditions in others, the NWS said.

Winter storm warnings, ice storm warnings and winter weather advisories were posted in and around Minneapolis and St Paul in Minnesota as freezing rain swept north through the region, followed by bands of heavy snow, according to the NWS.

The wintry blast, expected to spread into New England by Wednesday, was part of a larger weather front bringing heavy showers and a chance of severe thunderstorms, hail and tornadoes to the lower Mississippi Valley, Gulf Coast, Tennessee Valley and southern Appalachians.

Tornado watches and severe thunderstorm warnings were in effect across much of Louisiana, Mississippi, Alabama and Georgia, along with flood watches posted along the southern fringe of that zone.

"It's all part of the same system. The heavy snowfall is occurring on the west to northern side of the storm ... and then the rainfall and severe weather is across the south," NWS meteorologist Allison Santorelli said.

Nearly 200 flights through Minneapolis-St. Paul International Airport were cancelled on Tuesday, according to flight tracker FlightAware.

READ MORE: Death toll climbs as blizzard-battered US areas dig out

Floods expected in California

On the West Coast, northern California braced for another bout of heavy rain and flooding from an "atmospheric river" of dense moisture.

It was expected to bring drenching rains and the possibility of renewed flooding to northern and central California, starting on Wednesday.

California residents already experienced a catastrophic storm last weekend with deadly flooding.

An atmospheric river storm is a narrow but fierce current in the air that carries large amounts of water vapour as it travels from the tropics into the mid- and northern latitudes.

Rivers and the surrounding soil cannot accommodate the rainfall released, with atmospheric river storms the cause of extreme flooding and even landslides. 

Heavy snow was expected to return to the Sierra Nevada mountains on Wednesday, along with coastal rain and higher-elevation snow in the Pacific Northwest.

Santorelli said high winds accompanying the latest batch of impending downpours could uproot trees and knock down tree limbs, causing more blackouts.

As many as 21,000-plus homes and businesses in northern California were without electricity by early Tuesday, data from poweroutage.us showed.

Christmas week had already seen a winter storm that clobbered much of the US, starting with near-hurricane force lake-effect winds over the Great Lakes and driving snow in Buffalo, New York, that paralysed that city. 

Nearly 60 percent of the US population faced a winter advisory of some sort in the last two weeks of 2022, along with extreme temperatures and conditions, kicked off by a bomb cyclone in the Great Lakes, which is defined as a rapid drop in atmospheric pressure during a storm. 

READ MORE: Thousands of flights cancelled as US digs out from deadly superstorm