A potent winter storm that is expected to sweep across a large swath of the United States at the end of this week has prompted widespread unease as millions of residents prepared to face hazardous amounts of heavy snow and ice — though uncertainty remained on Wednesday about the storm’s exact timing, track and intensity.
By Wednesday morning, winter storm watches were in place from New Mexico, Oklahoma and central Texas through much of Tennessee, as well as Arkansas, southern Kansas and northern Louisiana from Friday through Sunday. Jennifer Tate, a meteorologist at the Weather Prediction Center, said for most of these areas, watches would likely be upgraded to winter storm warnings as the week goes on.
Here is what forecasters know so far:
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Cold, then snow and ice. Cold air is expected to surge into the Southeast on Thursday, ahead of snow and ice from Friday into the weekend.
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A significant and widespread storm. Confidence among meteorologists remained very high that a high-impact winter storm will unfold. Heavy snow, sleet and freezing rain are expected from the southern Rockies and Plains starting Friday, spreading east into the Tennessee Valley and the Southeast by Saturday and reaching the Mid-Atlantic and parts of the Northeast through the weekend, and possibly into Monday.
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Up to a foot of snow in places. From the southern Rockies and the Plains and east through the Mid-Atlantic, the storm will deliver mostly snow, and possibly a lot of it. Forecasters warned these areas were likely to face travel difficulties from snow-covered roads and reduced visibility.
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Dangerous ice. South of the snow, broad swaths of freezing rain and sleet are expected from the Southern Plains through to the Carolinas. In addition to treacherous travel, local officials are concerned about ice on trees leading to widespread power outages.
Here is what is uncertain:
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The magnitude of the storm. The storm’s expected trajectory has wobbled, so the total amount of snow, ice and freezing rain that each location will receive remains unclear.
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The exact location of where the storm develops and where it goes. This will determine where the dividing line between snow and ice. Forecasters said on Wednesday said that boundary had moved father north, increasing the risk of heavy snow across parts of the Northeast.
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How far north and south the heaviest snow will reach.
What forecasters are looking at:
Beginning Thursday, bitter cold air from the Arctic is expected to surge into the central and southeastern United States, said Owen Shieh, a warning coordination meteorologist at the Weather Prediction Center. Temperatures are expected to plunge as much as 30 degrees below normal, with wind chills — the combined effect of cold air and wind on exposed skin — dropping to around minus 50 degrees in the Upper Midwest.
With that frigid air mass in place, Ms. Tate said, as the storm develops and barrels east through the South starting Friday, it will pull moisture-rich air north from the Gulf of Mexico. that air will collide with the bitter cold, which will then produce those broad swaths of heavy snow, sleet and ice. These cold conditions, she added, could also allow snow and ice to linger into next week.
“It could be a problem in terms of keeping that snow and ice on the ground and not being able to melt so quickly,” she said. “So impact to travel in the southern Plains and Southeast could last longer.”
While confidence has been high from the outset that this will be a significant and widespread storm, some of the finer details have been difficult to pin down. Questions remained about the storm’s track, timing and precipitation amounts, all of which will determine where the snow and ice will ultimately fall, and how severe the impacts will be.
On Wednesday, forecasters said the projected path of the storm had shifted farther north. Ms. Tate said this adjustment means the areas impacted by the storm has now expanded, and the boundary line between snow and ice has also shifted north — but this does not mean areas in the Southeast are entirely in the clear.
“It still looks like there will be some ice in the Southeast, including areas like Georgia,” she said. “Because they will still have cold enough air at the surface to potentially get the freezing rain.”
While exact snowfall amounts and placement remain uncertain, Ms. Tate said on Wednesday that the latest forecast indicates accumulations could reach between eight and 12 inches in some locations, particularly in Oklahoma City, where the storm is expected to hit first, and in Nashville, as it moves east. Parts of the Mid-Atlantic, especially in Virginia and Maryland, could see more than a foot of snow.
Farther south, she said, the greatest risk for significant icing stretched from central Texas through to northern Louisiana, Mississippi, Alabama, Georgia and the Carolinas. Cities including Austin, Shreveport, Huntsville, Chattanooga, Atlanta, Columbia and Raleigh, could see a quarter to half an inch of ice accumulation, with locally higher amounts possible.
Nazaneen Ghaffar is a Times reporter on the Weather team.
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