The eastern United States is facing severe weather conditions, with blizzards in the North and floods in the South. Around 70 million people are under winter weather alerts from Nebraska to Maine.

The National Weather Service (NWS) has issued warnings for life-threatening flash flooding in the Southeast and heavy snowfall from the Upper Midwest to New England.

"As a low pressure system exits the western U.S. and moves into the central Plains early this [Saturday (February 15)], a high pressure system associated with a large pool of arctic air in Canada is poised to surge southward into the Plains. The interaction between the two systems will result in a rather large cyclone to develop and intensify as it tracks from southwest to northeast across the eastern half of the country through the next couple of days," the NWS said.

In the Southeast, areas like Kentucky and Tennessee are at high risk for excessive rainfall, with up to eight inches of rain expected in some places.

"Repeated rounds of intense storms will lead to rainfall rates of 1-2" per hour and totals of 3-6", with isolated amounts up to 8" as the storms move parallel to and back build along the front. The greatest risk for this intense rainfall prompting life-threatening flash flooding will be across portions of northwestern Tennessee and western Kentucky, where a High Risk of Excessive Rainfall (level 4/4) is in effect," the NWS warned.

The storm is expected to intensify over the weekend, bringing strong winds and potentially historic flash flooding to the Mississippi, Tennessee, and Ohio Valleys. There is also a risk of tornadoes in the lower Mississippi Valley.

"The severe weather event has the potential to produce multiple tornadoes in the EF0 to EF1 range," AccuWeather Severe Weather Expert Guy Pearson said, adding, "Some of the strongest tornadoes with the upcoming event from later Saturday to Saturday night will probably reach EF2 to EF3 intensity."

Meanwhile, the North is bracing for heavy snow, with double-digit snowfall expected in states like Michigan, Vermont, and Maine. The NWS warns of sleet and freezing rain in the Northeast, which could lead to power outages and hazardous travel conditions.

As the storm moves off the East Coast early next week, cold air is likely to persist across much of the eastern U.S.

In addition to the severe weather in the East, the Rocky Mountains are experiencing closures due to snow, and southern California is dealing with the aftermath of recent storms, including mudslides.

Simon Conway