The Busy Pattern Continues.
Last week’s installment headlined a progressive pattern that has been sending ridges and troughs west to east across the continent at a dizzying pace. That pattern produced some meaningful snow in the West earlier this week and then unloaded a blockbuster on the mid-Atlantic and much of the Northeast midweek, jumpstarting the season at dozens of resorts in the East as a result. The heavy snow did not extend to far northern New England, but snowmaking temps have been in place all this week so trail counts are on the rise.
For the foreseeable future, the fast moving pattern will continue with a tendency for upper level troughs to spend more time in the East then they did earlier in the season. Why the change? It has a lot to do with the phase of the NAO, or North Atlantic Oscillation. When the NAO is negative, we typically see an upper level ridge over Greenland and the waters to the south. In that position, it tends to slow down troughs as they move into eastern North America, giving them a chance to strengthen, spawn surface lows near the coast, and tap more in the way of cold air from Canada. That scenario unfolded this week during the current Nor’easter, and another storm could be in the cards again around Christmas Day. Here is a jet stream forecast for Christmas night that illustrates a classic negative NAO.
Prior to the arrival of the trough you see in the East, it will bring some snow to the upper Midwest on Christmas Eve, but in that position, a milder southwesterly flow will be in place further east. We could see one storm cut up through the Lakes, with a second storm then forming along the coast as the trough (and its cold air) tracks eastward. That could result in a rain to snow sequence playing out in the East on Christmas Day. Cold air will flow then into the Midwest and East early in the holiday week as the NAO will remain negative.
In the West, most of the action will continue to be focused in WA, OR, and BC, where shorter wavelength troughs keep rolling in from the Pacific Ocean. This weekend will bring a juicy system that originates further south, so it will lead to higher snow levels in the Cascades—as high as six-seven thousand feet. Snow levels will drop later Sunday into midweek, however, with fresh snow continuing through that period. Further inland, lighter snows will be common for the first half of next week in ID, MT, and WY. South of there, fresh snow will be scarce next week due to the presence of a flat ridge that doesn’t want to give way to systems from the north. Now, if you take a look at the jet stream map again, you will notice a large blue blob just off the west coast around Christmas Day. That trough will likely move toward the coast and perhaps bodily move inland early in the holiday week. That could turn into a very productive storm across a wide swath of the West. So, COVID restrictions aside, the holiday period is starting to shape up. Better late than never.
Regional Details
Northwest U.S./Western Canada: Plenty of snow in the next week, but with bouncing snow levels in the Cascades. A snowy, colder trough arrives just after Christmas.
Sierra: A quiet week leading up to Christmas. Prospects for snow improve after that.
Rockies: Light to moderate snows across the north leading up to the holiday keep surfaces soft and boost trail counts. Central and southern resorts waiting for the post-Christmas trough.
Midwest: Light snow early next week, more significant snow looking good for Christmas Eve. Good snowmaking temps much of the time.
Mid Atlantic/Southeast: Nice weekend on the slopes after fresh midweek snow. Milder next week. Colder after Christmas.
Northeast/QB: Quiet until Christmas storm that brings rain to snow. Wintry pattern during holiday week.
