New Round of Snow and Ice for the U.S.; Extreme Warmth in Alaska

The calendar says we’re still a month and a half away from the peak of winter, but the winter weather gripping most of the U.S. is more typical of mid-January, as a significant outbreak of Arctic air continues to bring temperatures 10 - 30 degrees below normal to much of the nation. Following last Friday’s major winter storm that brought heavy snows and significant icing from Texas to Maine (“Cleon”), a new winter storm dubbed “Dion” followed a similar track on Sunday. The storm brought the first snow of winter to Washington D.C., New York City, and Philadelphia (the average date of the first measurable snow ranges from Dec. 14 in Baltimore to Dec. 18 in Philadelphia and Washington.) The 8.6” of snow that fell on Philadelphia surpassed the snowfall total for the entire 2012-2013 season (8.3”.) Snow and blowing snow hit four NFL games on Sunday—Lions at Eagles, Vikings at Ravens, Chiefs at Redskins, and Dolphins at Steelers—so obscuring the yard markers, that it was almost impossible for fans to tell exactly where the ball was at all four stadiums. The snow caused multiple traffic accidents that shut portions of I-95 in Philadelphia, and all planes were grounded at the airport during the afternoon. Farther west in Pennsylvania, heavy snow caused a 56-car pile up on the westbound lanes of the Pennsylvania Turnpike from Downingtown to Morgantown, after a motorist got out of his car after a minor accident and was hit and killed. One other person was injured. I-78 in Pennsylvania was also closed by traffic accidents on Sunday. More that 1/4” of ice accumulated due to freezing rains in portions of Kentucky, Tennessee, Virginia, Maryland, and West Virginia.


Figure 1. Pregame festivities at Sunday’s Lions-Eagles game in Philadelphia looked like a scene out of “Frozen.” Image credit: CNBC's Jim Cramer (@jimcramer)

Severe cold wave due to an unusually extreme jet stream kink
As we’ve so many times over the past few years, the jet stream is stuck in an unusually wavy configuration that is bringing remarkable hot and cold weather extremes to the entire continent. A sharp trough of low pressure over the center of North America is allowing frigid Arctic air to barrel unusually far south, setting hundreds of daily records over the past few days. Temperatures in Northern Montana were as much as 50 degrees below normal, and in portions of Oregon, the cold blast brought the coldest temperatures since 1972. One station even set an all-time cold record: Lakeview, Oregon hit -27° on December 8, breaking the old all-time cold record of -24° set on Jan. 15, 1888. Temperature records there began in 1884.

Unusually extreme ridges of high pressure set up over Alaska and the Southeast United States to compensate for the big dip in the jet stream over the center of North America. One ridge of high pressure pushed to the north of Alaska and over the Arctic Ocean, allowing warm Pacific air to bring rain and temperatures in the upper 30s to Alaska’s North Slope on Sunday—an unprecedented occurrence in December. Keep in mind that this is an area that has been in perpetual 24-hour darkness for several weeks. According to wunderground’s weather historian Christopher C. Burt, it appears that Sunday’s 39° at Deadhorse (Prudhoe Bay) is the warmest December temperature ever measured at any site on the Alaskan Arctic Ocean shoreline region. Weather records for Alaska’s North Slope go back as far as 1921 at Point Barrow. A very sharp ridge of high pressure also set up over the Southeast U.S.—Tallahasse, Florida hit 84° on Saturday, matching their highest temperature ever recorded in the month of December.


Figure 2. Jet stream winds over North America on Sunday, December 8, showed a sharp trough of low pressure over the center of the continent, allowing cold Arctic air to spill southwards into the U.S. Sharp ridges of high pressure were over Alaska and the Southeast U.S.

Jeff Masters