Meteorologists are anxiously eyeing a developing storm system that could bring a dangerous nighttime severe thunderstorm outbreak and dump a swath of moderate to heavy snow. The National Weather Service is even warning that “strong” tornadoes are possible across the mid-South and Tennessee Valley on Wednesday night, a threat that will continue Thursday from the deep South to the Ohio Valley.
It’s the same storm system that delivered a rare burst of snow to the Desert Southwest on Tuesday into the night. Snowflakes were seen around Las Vegas and Tucson, where such wintry weather is rare. Now nearly 20 million Americans are under winter weather advisories or winter storm warnings, and plowable snow on the cold side of the system is expected to plaster a 1,200-mile swath from Colorado to Michigan.
Strong winds surrounding the system caused a dust storm across portions of Oklahoma, which resulted in a deadly 10-vehicle pileup in the Panhandle on Tuesday. In eastern New Mexico and adjacent west Texas, those gusts have prompted wind advisories and high-wind warnings, and raised concerns for fire danger in the Big Bend and Permian Basin areas.
Ahead of the storm, abnormally warm conditions are surging northward from the Tennessee Valley to the Northeast, where the Weather Service predicts at least two dozen record highs could be threatened Wednesday afternoon. Temperatures are forecast to soar into the 60s and 70s — which would be up to 25 to 35 degrees above normal.
The storm won’t be quite as intense when it reaches the East Coast on Friday morning, but it will generate the possibility of gusty downpours from Atlanta to Boston during the first half of the day, with snow relegated to interior northern New England. Much colder air will pour over the East in the storm’s wake.
The setup
At the root of the meteorological malice is a low-pressure system over the Four Corners, which was transferring its energy to a new fledgling low taking shape over the Oklahoma and Texas panhandles. That nascent low will intensify as it pushes into Arkansas and, by early Thursday, slips north of the Ohio River and into the Midwest.
Lows in the northern hemisphere spin counterclockwise. That means mild, moisture-rich air is pumped north ahead of the low, with cold and crisp Canadian air dragged south in its wake. The two air masses collide along a cold front, which trails south of the low.
Severe thunderstorms are set to erupt in the system’s “warm sector.” And in the cold sector — heavy snow.
Dangerous severe weather
The severe storms are forecast to erupt between eastern Texas and southwestern Kentucky on Wednesday into the night, and between southern Louisiana and Ohio on Thursday. A breakdown of the areas most at risk and the potential hazards are provided below.
Wednesday
Areas affected: The Weather Service’s Storm Prediction Center has drawn a level 3 out of 5 “enhanced risk” zone that covers areas between Little Rock and Jackson, Tenn. That includes Memphis, Pine Bluff and communities along Interstate 40. Northwest Mississippi is encompassed too, primarily west of Interstate 55. The remainder of Arkansas, a stretch of northeast Texas including Dallas, southern Missouri and western Kentucky including Paducah are under a level 2 out of 5 risk.
Timing: A broken line of thunderstorms will develop during the evening between Dallas and southern Oklahoma along Interstate 35. As that line of storms moves east overnight, it will also expand to the north. After nightfall, however, a few isolated rotating thunderstorms or supercells may form in eastern Arkansas or along the Mississippi River and work into western Tennessee. That would be of significant concern for Memphis.
Hazards: Within the line of storms, strong to damaging straight-line winds with gusts up to 60 mph will be possible, along with a low tornado risk. If any supercells develop, they could yield a strong tornado risk, as well as produce some hail.
Thursday
Areas affected: Another level 3 out of 5 risk zone encompasses eastern Mississippi, northwestern Alabama, central Tennessee, southwest Illinois and a swath of Ohio, and includes the cities of Birmingham, Nashville, Louisville and Cincinnati. A surrounding area, including the rest of Alabama and Mississippi, is under a level 2 out of 5 slight risk.
Timing: Thunderstorms left from Wednesday night will be decaying during the morning hours, but will be reinvigorated by lunchtime Thursday as daytime heating kicks in. They’ll work east during the afternoon. A few messy clusters could develop ahead of the main line, but if any take on supercell characteristics, the tornado risk would be greater.
Hazards: Once again, the line of storms will deliver mainly straight-line winds and isolated tornado spin-ups. If any supercells form, a strong tornado threat could occur — especially in eastern Mississippi and west-central Alabama.
Heavy snow
A pocket of frigid air aloft was helping produce mountain snow over Arizona and New Mexico on Wednesday. A more solid batch of snow was targeting Colorado. Winter storm warnings cover central and southern Colorado, though Denver is under a winter weather advisory. Northern Kansas, southern Nebraska, northern Missouri and southern Iowa are all under winter storm warnings. The alerts also bleed into the northwesternmost two counties of Illinois.
Moderate to heavy snow will fall in the “comma head” of low pressure, or the moisture wraparound, which arcs counterclockwise back into the regime of cold air arriving on the back side of the system.
“Travel could be very difficult,” wrote the National Weather Service in Hastings, Neb. “Areas of blowing and drifting snow could significantly reduce visibility.”
The steadiest snow was expected to fall over the central Plains from late Wednesday afternoon through Thursday morning, before expanding northwest through southern Wisconsin and central Michigan.
A general 4 to 8 inches will fall within the swath of heaviest snow, which includes St. Joseph, Mo.; Cedar Rapids, Iowa; and Milwaukee.
Around Chicago, a wintry mix is expected Wednesday night into Thursday night, with freezing rain and sleet eventually transitioning to snow.
A snowy night in Tucson is not something you see very often, but here we are! A light coating on cars and grassy surfaces is likely as the heavier band of precipitation moves through the area. #azwx pic.twitter.com/wCIEYEJrKP
— NWS Tucson (@NWSTucson) February 15, 2023
In the Southwest, where the storm was pulling away midday Wednesday, Tucson picked up at least 0.6 inches of snow. An average winter nowadays features only 0.2 inches; no measurable snow fell last year. Snowier Flagstaff received nearly 9 inches, while as much as 25 inches of snow fell in southwest Colorado and 15 inches in the mountains of northern New Mexico.
Jason Samenow contributed to this report.