The calendar has turned to December and the signs are there for a very winter-like pattern across much of the nation during the next couple of weeks – the likes of which we haven’t seen in quite some time for this early in the winter season. An incredibly cold Arctic air outbreak is now gathering itself just above the US/Canada border region in southwestern Canada and it is about to plunge into the Northern Plains and Rocky Mountain region with painful results and temperatures some 40 degrees below normal. Temperatures by Wednesday and Thursday won’t rise above zero in parts of North Dakota and Montana and overnight lows could bottom out at 30 degrees below zero (GFS surface temperature forecast map for Thursday evening courtesy weather.cod.edu). Denver will experience plunging temperatures on Tuesday and might not be able to climb above 10 degrees on Wednesday and Thursday. To make matters worse, snow and wind will accompany this Arctic blast across the Rockies and Northern Plains during the next 48 hours or so.
This Arctic blast will continue on a trek towards the eastern states and could lead to potential problems for the Mid-Atlantic region. The initial cold front will likely pass through the Mid-Atlantic region by Friday or so, but it will then get hung up in a southwest-to-northeast direction not far from the east coast. At the same time, an active pattern may then produce wave-after-wave of low pressure that will ride along the frontal boundary from the moisture-laden Deep South towards this region. This type of pattern could ultimately lead to significant ice around later this weekend or early next week or even accumulating snow. There are signs for a second Arctic blast next week that will again affect much of the country. Stay tuned.