Early-season precipitation builds up in the Pacific Northwest before moving over the southern and eastern Great Lakes and passing through the Appalachians, the National Weather Service says.
This snow-frost connection isn’t unusual in the northern US, where snowfall is more common than snow on the other side of the Mississippi River in the south. By the time the snow begins to accumulate over the Upper Midwest and the Ohio and Tennessee valleys in mid- to late-December, snow usually has mostly melted over the Rockies and the Sierra Nevada, according to the US National Snow and Ice Data Center.
Snow, rain and wind “is not your typical winter weather,” Nate Davis, a meteorologist at the National Weather Service’s Weather Prediction Center in College Park, Maryland, said in a phone interview from his office in College Park. “Here it’s going to be wet and windy, and it’s going to feel colder than the 30s [degree Fahrenheit] where the snow will be.”
There’s no need to panic: the mild part of the weather pattern is due to the jet stream, a fluid of winds at about 35,000 feet that routes storms across the nation, said Max Gonzalez, a meteorologist at the National Weather Service’s Weather Prediction Center in College Park. The jet stream system reaches as far south as the Gulf of Mexico in the winter, or as far north as the frozen Atlantic in the summer. “Winter is not ahead,” Gonzalez said.
Temperatures will hover about a degree above normal for much of the central and eastern US through the start of next week, Davis said, adding that this winter’s relative warmth is another factor. A week ago, the 10th-warmest December on record was predicted, meteorologists at NOAA’s Climate Prediction Center in College Park, Maryland, said in an online outlook on 12 December.
A storm system pushing up the eastern seaboard from the northern Rockies will drag more mild air southward during the week, and “make for a rare and uncommonly mild Great Lakes region”, according to AccuWeather Inc. This week’s warmth may push highs to around 30C (86F) in parts of Minnesota, Illinois, Indiana and Ohio, the Buffalo, New York-based forecaster said on its website on 12 December. Higher elevations on the North Slope of Alaska are expecting temperatures as high as 40C.
Still, almost half of the nation will remain under “below normal” temperatures for the rest of December, even with the recent warmth, according to the Climate Prediction Center. Some parts of Canada and southern Mexico will be warmer than normal, and Hawaii will remain at a below-normal level. Temperatures will be in the high teens and lower 20s in New England from the 14th to 23rd, and in the 40s in New York and the 40s and lower 50s in Washington.
In the northern New England states, it’s warmer in the winter so far than it usually is, bringing an economic boost to regions that use this time of year to build or repair trails, bury snow and clear parking lots, Gonzalez said. Ski resorts in New Hampshire, Maine and Vermont have been benefiting from milder temperatures.