Major Storm On the Way

Fri 3/7:

Rainfall - For several days now computer guidance has been hammering home the idea of a widespread heavy rainfall across nearly all of Central and Southern New England (and much of the East Coast for that matter) and today we can clearly see what the models were dreaming up - just look at the National Radar. Clearly, there is a lot of water ready to invade New England and it appears as though Southern New England is under the gun for the highest totals.

I would place the heaviest axis of precipitation somewhere in the triangle of New Haven, CT to Groton, CT to Boston, MA - where someone could easily get 4" of rain. Lesser amounts, but still sizable totals, will be found either side of this region. Here on Cape Cod, we should expect a solid 2" rainfall, with possibly as much as 3" on parts of the Upper Cape. Computer guidance has consistently cranked out between 1.8 and 2.8" at Chatham - and given the origins of this storm system (the Gulf of Mexico) these numbers could be a bit conservative thanks to some heavy downpours.

This heavy rain will come in two main waves, one tonight and another Saturday afternoon. The first slug of rain should yield 1/2 to 1 inch of rainfall, with the second round dumping another 1 to 2 inches by Saturday night. Tonight's rain will be of a steadier variety (though still potentially heavy at times) owing heavily to the displacement of cool air in New England. Saturday's rainfall will tend to be more convective in nature as we scour out the cold and get into the warm sector of the storm. With so much heat being driven northward up the Eastern Seaboard, conditions will be favorable thunderstorm development (in fact, we won't be far removed from the threat for severe weather which will push well up the coast into the Mid-Atlantic) - so expect downpours Saturday with gusty winds as well.

Wind - Speaking of gusty winds, there are two windows for some strong winds with this storm system. A powerful low level jet will develop out ahead of the storm center, lift up the East Coast and cross the region tonight and tomorrow, presenting our first opportunity for strong wind. How much of this initial jet is able to interact with the surface will be dependent upon just how mild things get in the southerly flow behind the strong warm front late tonight. If we could hit the 57F on Saturday that some computer guidance suggests, the stabilizing low level inversion would be awfully close to disappearing. But can we get that warm?

With water temps at their climatological bottom, it won't be easy to bust well into the upper 50s. We will likely fall just shy (50-55F?) - but computer guidance did underestimate the amount of warmth carrying up the coast earlier this week. Either way, it's going to be a close call and it's going to be windy with southerly winds gusting to 40 mph during the first window (mainly very late Friday night and into Saturday). The second opportunity for wind comes on the underside of the storm when pressures start to rise, winds shift to the west-southwest and much colder air rushes into the region. Latest MET guidance has a 31 knot sustained wind at Falmouth at 1AM Sunday morning - with mid to high 20 knot values lasting into a good portion of Sunday. That's awfully close to damaging wind criteria. Look for some kine of wind alert to be issued by the National Weather Service.

This entire mess pulls away during the second half of the weekend, leaving us with much colder but drier conditions to start next week. I expect temperatures to be stuck in the 30s for highs Sunday, Monday and Tuesday, with overnight lows dipping into the 10s and 20s. Our next shot of any meaningful weather will be Wednesday when a clipper system drops into the Northeast. We'll track this closely, as there's a small chance this feature could try and wrap up just east of New England.