Not much snow cover yet south of Canadian border; cooler weather the next few days, then milder for weekend
We’ve talked quite a bit about the thick snowpack covering much of Canada and how that will help (and is helping) cold air pool and recharge north of us, a source that will be tapped from time to time this winter and may eventually sink south in a much larger way. However, looking south of the border, there is an unusually small amount of real estate covered by snow in the United States (not including Alaska). As of Tuesday, only 7.6 percent of the U.S. had snow cover, mostly the higher elevations of the western mountains. In each year from 2006 to 2011, there was 25 to 33 percent snow cover in the lower 48 by this time. And in 2005 there was more than 45 percent. You have to go back to 2003, the first year the remote sensing snow cover data is available on the web site linked here, to find a year with even similarly low snow cover in the U.S. by early December — about 13 percent — and that changed quickly with a winter storm that gave our region about half a foot on Dec. 5-6. Factors at play in lack of snowfall: The predominant west-southwesterly flow around the dominant Pacific Northwest low-pressure vortex (the PNA-negative pattern), ongoing drought in large parts of the country, and the utter lack of a discernible southern branch of the jet stream pumping wet storms off the Pacific across the southern half of the U.S. There are some changes developing that will likely turn more of the country white and wet — more so over the central U.S. than here.
We have a cold front moving through this morning that will pull temperatures back the next few days — only a little cooler today with highs around 60, but closer to 50 on Thursday, and lows going back below freezing most spots the next 2 or 3 mornings. We warm up again for the weekend, at least with some 60s, before another cold front in the early to middle part of next week brings a somewhat sharper, but still short, shot of cold air. This front and low-pressure system have the potential to bring us more widespread rain than we’ve seen in weeks, but it appears as if the heaviest rain will move into the Ohio Valley, with some heavy snow on the backside of the storm farther west.