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After transient warmup, winter set to return

This is not the news many were hoping to hear this morning. Unfortunately, it’s the news we have to provide as a result of medium and long term forecast modeling and the overall hemispheric evolution over the next two weeks. Luckily for those who enjoy the warmth, today looks to be the winner of the week. Behind a mid level atmospheric disturbance which provided the area with rain on Tuesday, warm mid level temperatures will remain in the area on Wednesday. Periods of sunshine and west winds will allow temperatures to rise into the mid to upper 50’s throughout the area. Some areas will approach and may even exceed 60 degrees during the afternoon. Others, especially near the shore, will remain slightly cooler.

The warmth, as is often the case this time of year, won’t last long. Colder mid and upper level temperatures will push southward on Thursday and Friday and temperatures will move back toward more normal levels. The transient pattern will continue through the weekend as another disturbance approaches — bringing precipitation mainly in the form of rain, as temperatures briefly warm up once again before crashing back down on Sunday. Still, that will be just the beginning of the trend toward a colder, more active pattern which will establish itself in the medium to long range.

The transition begins in the upper levels of the atmosphere as early as this weekend. As many in the meteorological community may be well aware of, one thing we have lacked this winter has been high latitude blocking. In a simple sense, high latitude blocking is the development of ridging or higher than normal heights in the mid/upper levels of the atmosphere in the higher latitudes. In the NAO region, high latitude blocking can develop over the North Atlantic and, when especially anomalous, can move westward toward the Davis Straight and Central Canada. This blocking acts to do several things but, most notably, it slows down the mid level atmospheric flow and dislodges cold air over the Northern 1/3 of the United States.

GFS Ensembles showing a heightened probability of 850mb temperatures less than -10 C next week.

GFS Ensembles showing a heightened probability of 850mb temperatures less than -10 C next week.

The absence of this blocking has shown its face this year many times. Remember Juno, slipping slightly east of our area? It’s not fantasy to speculate that the storm would’ve been deeper and closer to the coast had high latitude blocking been present to slow down the mid level flow. But, I digress. The main point here is that forecast models are in good agreement that this high latitude blocking will, in fact, develop for the first time this winter season beginning this weekend and continuing into next week. It is first seen in an anomalous ridge in the North Atlantic, and then expands to Greenland and Canada.

Medium range forecast models have been targeting this period for several days now — and we have seen a continued trend toward heightened high latitude blocking during this time frame as time goes on. Both the GFS and ECMWF Ensemble means are in good agreement on its development.

GFS Ensemble mean showing above normal heights in the high latitudes and lower than normal heights over the Southeast US.

In fact, the ridging develops on both sides of the playing field, per say. A large ridge on the West Coast of the United States surges northward into British Columbia and Western Canada, while higher than normal heights expand from Greenland into Central Canada and the Davis Straight. Accordingly, a lobe of the Polar Vortex is dislodged southeastward over Southeast Canada and Northern New England by the early to middle part of next week. The sensible weather effects? The return of colder than normal air and brisk northwesterly winds — as well as returning chances for wintry precipitation as we move through the end of March.

Pinpointing the potential for winter weather, at this range, is incredibly difficult. We are still at a lead time where details are quite uncertain and intricacies of the pattern will be almost impossible for forecast models to key in on. That being said, there are several potential “events” appearing on medium range forecast modeling which, more than anything, is a sign of the potential which exists within the pattern. Perhaps a harbinger of things to come, the long range GFS and ECMWF have both shown Nor’Easters during the last week of March at some point over the last 2 or 3 days.

For now, though, it becomes much too difficult to pinpoint any specific threat. Instead, we have done our best to analyze the pattern and target the period for both the return of cold air and potential winter weather. As we have said many times this winter: Stay tuned.

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