Weekend Trouble?

WED 3/12

The rest of the work week will be relatively quiet, with one small system crossing Wednesday and another passing through Thursday night and Friday. While the weather won't be great during this time period, as each of these systems will provide pockets of clouds and light precipitation (some snowflakes Thursday night?), there are no big storms on tap through Friday and there shouldn't be any difficult weather to contend with during the short-term. However, despite the relative tranquility, these small weather systems will actually play a big role in what happens over the weekend as they will help establish a growing temperature gradient somewhere near or south of New England. This gradient may ultimately feed and guide a much stronger storm toward the region Saturday and Sunday.

The temperature gradient in question actually extends westward all the way to the Central Plains, as cold air near the US/Canadian border pushes southward against mild temperatures stretching through the Southern US. This east-to-west temperature boundary will eventually become a focal point for storm development later in the week, as jet stream energy emerging from the Rockies moves out into the plains and heads eastward along the temperature gradient.

As the jet stream energy comes out of Colorado, a low pressure area will take shape over the south/central plains and subsequently strengthen and track through the Ohio Valley and head toward the Mid-Atlantic by the weekend - riding nearly due east along the aforementioned boundary. This storm is destined to spread a shield of wintry precipitation to the north of its track, with perhaps some sizable snow accumulation in places.

For us here on Cape Cod, it's what happens by Saturday and Sunday when the storm reaches the Eastern Seaboard that is most important. Unfortunately, this remains very much in question and is highly dependent upon the subtle interaction of several air masses and the strength of the jet stream energy spawning the storm.

Behind Friday's disturbance, slightly cooler air will be oozing southward through New England on Saturday. This cooler air and corresponding lower atmospheric heights should be just enough to force the approaching storm on a track south of New England - but how far south? Much of that will be determined by the upper level energy spawning the storm.

There's a large discrepancy in forecast guidance as to the strength and position of said jet energy. Some guidance (GFS, ECMWF) keeps the energy flatter and progressive, resulting in a corresponding weak and fast moving surface low pressure that stays rather far to the south. Such a set-up would yield a quieter weekend with the storm system possibly missing the region altogether.

However, there's another cluster of models, that allows for stronger, more closed off upper level support. This subsequently produces a stronger, slower, further north and more developed surface low pressure. In fact, if we carry a model such as the NAM/WRF out to its extended counterpart, the DGEX, we end up with a *powerhouse* low pressure system south of Nantucket on Sunday. This is similar to the Canadian model and even close to where the EURO model was on this last weekend when the storm was still 240 hours away (the EURO, incidentally, is now in the more suppressed cluster of guidance).

Despite the contrasting solutions (the differences between the U.S. models, the NAM and the GFS, are remarkable), I think the makings are here for this storm to be quite a player in our weekend weather. Just looking at the large scale (Northern Hemisphere) picture, numerous factors are coming together to support a strong east coast low pressure area somewhere east of Cape Cod. The potential is certainly here for a strong storm to develop, with rain actually transitioning to snow during the event and strong northeast to northerly winds kicking in. For now, I've simply continued the theme of an unsettled weekend forecast awaiting future information.

It will certainly be interesting to track this over the next 48 to 60 hours as the models get a better handle on the upper level energy involved.