A frigid, snowy pattern could invade the U.S. during Christmas week
At the same time, the likelihood of significant winter storms in the eastern half of the country between Wednesday and Christmas Eve is increasing. While far from a floodgate, Mother Nature can bring a white Christmas to part of the Midwest and Eastern United States.
The cold weather and possibility of snow coincide with a peak time for leisure travelers.
After a week or so, it is not possible to predict exactly where a storm may form and which areas will see snow, rain, or remain dry. But between Dec. 22 and Dec. 24, the likelihood of a significant storm between the Midwest and the East Coast is above normal.
The primary buildup for our potential winter weather outbreak involves the buildup of strong high pressure over the eastern Pacific toward the Aleutian Islands of Alaska.
This high acts as a force field, deflecting the jet stream around it. The jet – separating cold and milder air – will curve toward the Arctic Circle in central North America before plummeting south over the central and eastern United States.
We can look at a model of the trajectories of air packets in the atmosphere for clues as to the origins of next week’s air mass. If we run the model for Christmas Eve in the Midwest, it traces the air back to Nunavut, Canada, between the Northwest Passages and Baffin Bay, bordering Greenland.
The initial cold snap will move south into the northern Rocky Mountains and northern plains on Monday and Tuesday, reaching the Great Lakes Tuesday through Wednesday. Some of the coldest areas near the border with Canada could reach temperatures of 30 to 40 degrees below normal, meaning highs around minus 10 and lows of minus 20 to minus 30. Sub-zero temperatures could extend to the central plains in the south.
The core of the cold will likely remain over the northern United States through midweek, although temperatures 10 to 20 degrees below normal could reach parts of the southern and eastern United States late in the workweek.
A second, intensifying cold snap may plunge into the northern plains and upper Midwest on Wednesday and Thursday, pushing cold air even further south and east. Minneapolis should expect lows well below zero, while Chicago could see only teenage highs for much of the second half of next week.
Temperatures on Christmas Eve and Christmas Day can range from 10 to 30 degrees below normal across much of the eastern half of the country.
There are signs that a third shot of cold air could enter the northern plains around Christmas Day, before heading south and east in about 10 days.
The National Weather Service’s Climate Forecasting Center sees high probabilities for below-average temperatures in the central and eastern states both 6 to 10 and 8 to 14 days into the future.
The potential for snowfall will extend from the plains to the east coast for the second half of next week. Here’s what we know:
- central states: As the jet stream dips south over the Plains, a disturbance embedded in that flow could cause some snow to break out over the central and northern Plains before sweeping across the Midwest, Tennessee, and Ohio valleys. The exact trace of a disturbance is still unclear, as is the position of the rain/snow transition line; The timing would probably be around Wednesday through Thursday.
- Mid-Atlantic and Northeast: The disruption, which could bring snow to the central states, could develop into a major East Coast storm. It would have plenty of jet stream energy to feed on and could draw copious amounts of moisture from the Atlantic Ocean. However, it is still very uncertain if and where a coastal storm could form and which areas will be hardest hit. The timing of this storm would likely be between Thursday and Christmas Eve.
It’s important to remember the rough timeline meteorologists use to make forecasts — considering the first cold spell is three days away and the possibility of a storm is five to seven days away:
7 to 10 days in advance, Forecasters can identify large-scale patterns favorable to blows of cold (or warm) air and large storms. That means estimating the approximate shape of the jet stream, which would provide insight into temperature trends – and where storms might form.
Five to seven days in advance Forecasters can begin by estimating temperature differences from normal. That’s why they can say, for example, that the upcoming air mass over the plains has the potential to be 30 degrees or more colder than average. You can also start to discern the ingredients needed to create a storm – but can’t yet tell if they’re overlapping just right.
Three to five days in advance Forecasters can forecast high and low temperatures with sufficient accuracy for planning purposes. They can also tell if a storm will form and roughly estimate how strong it will be. They might also be able to determine where a storm will go within about 100 miles in either direction. They cannot yet give reliable forecasts of specific amounts of rain or snow, as small shifts in the trail could alter these amounts significantly.
A day or two in advance Forecasters know where the storm will go, how much rain or snow will fall, how strong the winds will be, and how long it will last. They can provide specific snowfall forecasts and guidance for planning purposes.
During the day, Forecasters can identify “mesoscale” influences, or estimate how smaller features (about the size of a few counties) will affect conditions locally. That could mean pinpointing exactly where a 10-mile-wide stubborn band of snow will form or where an afternoon’s greatest tornado threat might lie.
