It’s that time of year. Nor’easter season is here and it looks like we’ll have quite a little storm come Wednesday night. This nor’easter won’t deliver much wintry precipitation to Connecticut but rather a period of heavy rain and gusty winds.
Here’s the 12z Euro model 96 hour forecast valid 12z Thursday. On the left is 850mb temperatures (~5000 ft up) and wind speeds while on the right is SLP, 1000-500mb thickness, and QPF.
Sub-freezing forecast 850mb temperatures on the storm’s northwest flank may be cold enough to produce some snow and/or sleet up in the Berkshires, Catskills, or Poconos which isn’t terribly unusual for the time of year.
While our models differ on the specifics, the GFS and Euro show a similar setup with a low “bombing” out off the North Carolina coast. A shortwave, diving through the southeastern U.S. (labeled #2), will effectively get captured by by another, amplifying, shortwave trough (labeled #1) becoming negatively tilted. Here’s the evolution on the 18z GFS 500mb forecast between hours 36, 48, and 60 from left to right.
This setup isn’t unusual but it’s not particularly favorable for New England snow in early November as modeled. Why? The phase will occur too early. Here’s the 72 hour GFS 500mb and SLP forecast.
The storm intensifies rapidly but it does so well south of us – becoming mature off the Delmarva. By the time it meanders toward Connecticut it begins to fill as the synoptic/quasi-geostrophic forcing weakens. This time of year, with little antecedent cold air, you want the storm bombing as close to you as possible in order to get snow! Strong upward motion can help cool the atmosphere and maintain a zone of relatively chilled mid level air.
In this case, with a storm holding its own or filling as it approaches southern New England, wintry precipitation should be short lived and likely confined to the Berkshires, Greens and Catskills where some accumulation is possible.
Things can change, of course. A later phase (a la 00z NAM) would result in more intense vertical motion over the region. This may result in enough dynamic cooling to produce a thump of snow. An overperforming cold/dry high to the north of New England is another possible way to get a more wintry scenario. The vast majority of models, including the GFS ensembles, are far too warm for anything more than a few sloppy flakes or sleet pellets.
The 18z GFS shows an impressive low level jet with ripping northeasterlies at 900mb up to 80 knots. At 00z at HVN you can see the potential for a bit of mixing up to about 500 ft AGL. I wouldn’t be surprised to see wind gusts as high as 50 m.p.h. along the shoreline during the peak of the storm. This will obviously be well short of what we experienced during Sandy but it will make for a pretty ugly Wednesday evening.