U.S. Weather Returns to Its Climatological Senses, and Then Some

After a markedly mild November marked by thousands of daily record highs and less than 100 record daily lows (more on that in our upcoming monthly roundup), it will feel much more like December across the bulk of the contiguous U.S. over the next couple of weeks. Some locations may see their coldest weather in years as a series of Arctic high pressure cells swing through western Canada and southward across all but the Desert Southwest.

A sneak preview of the wintry weather to come hit parts of the Midwest on Sunday, when an anticipated light snow turned out to be a more efficient producer than expected. The 6.4” of snow at Chicago’s O’Hare International Airport was the city’s heaviest December snowfall since 2005. It was also more snow than Chicago obtained in December 2014 and 2015 combined (4.5”). Snowfall records for December 4 were set at Chicago as well as at Moline, IL (7.8”) and Madison, WI (5.7”). This fast-moving but mostly light snow shield will scoot across New England on Monday.


Figure 1. The first snow of the season descended on Sturgeon Bay, Wisconsin, on Sunday, December 4, 2016. Image credit: wunderphotographer lablover47.

A brief warmup for much of the central U.S. on Monday will be followed by the first of several Arctic blasts, each more intense than the last. The first front will push from the Northern Rockies on Monday into the Midwest on Tuesday and the Northeast by Wednesday. A stronger reinforcing shot will kick in later in the week, with that front pushing all the way through the Gulf of Mexico and across Florida by the weekend. Most of the Plains and South will see temperatures as much as 20 - 25°F below average late this week. A widespread, crippling snowstorm isn’t expected, though the Front Range of Colorado may get a few inches by Wednesday. Favored lake-effect-snow regions near the Great Lakes could get hammered late this week as the frigid air approaches from a favorable direction and passes over waters that are running 5°F or more above average in many locations.


Figure 2. Low temperatures projected by the GFS model run from 00Z Monday show that temperatures at 12Z Friday, December 9, 2016 (6 AM CST/7AM EST) may dip below freezing as far south as southern Louisiana and the northwest Florida panhandle. Image credit: tropicaltidbits.com.

More to come next week?
In the longer range, the GFS and ECMWF models indicate that the mid-level polar vortex may split in two next week, with one lobe shifting into Canada, the other perched atop western Russia, and a strong ridge extending from the North Pacific into the Arctic. If this pattern materializes, especially as depicted by the GFS, it would be conducive for additional Arctic surges into the contiguous U.S., likely bringing the coldest air of the year so far. Many record lows in December were set decades ago, during a notably cooler U.S. climate, so it’s typically difficult to match those readings without a truly intense cold shot. Still, it wouldn’t be surprising to see a good number of daily record lows (and record-low maxima) challenged if not broken next week should the projected pattern take hold.

Bob Henson