Friday Update

In a possible ominous sign I woke up this morning from a nightmare in which the 17.5″ of snow I have on the ground outside my house had melted entirely. Not even a snow pile to be found at the end of the driveway. Clearly, this is yet another sign I suffer from the illness known as “weather obsession.”

What this portends for the weekend storm I do not know. A surprise burst of very heavy snow or a storm that winds up being a bust?

Let’s try to answer that question the best I can. Let’s start out with the short range ensemble forecast or SREF. I normally don’t find these terribly valuable in southern New England during the cold season but this winter I haven’t found them totally awful.


This shows the amount of liquid expected to fall in Windsor Locks from a number of high resolution computer models – each with different physics and parameterizations. The ensemble mean is close to 0.5″ while the best “clustering” of ensemble members is around 0.35″. You can see some outliers that produce much higher precipitation totals. Assuming a liquid:snow ratio of 12:1 you’re looking at about 4″ of snow for the majority of the ensemble members.



The most impressive solution here in southern New England is the GFS model which develops the most intense low pressure near eastern New England. Here about 10,000 ft off the ground you can see a back-bent warm front which is a classic sign of a mature storm. Along that front strong “lift” in the atmosphere can produce heavy snow.

In addition the GFS shows very impressive “snow growth” with the strongest lift centered around -15c from Saturday evening through Sunday morning.



This is a VERY impressive signature and if it were to verify our snowfall amounts would be underdone significantly. However, other models are not nearly as bullish with the amount of “lift” modeled in the atmosphere. You need lift (we call it omega) to get precipitation!


The NAM insists on keeps 2 areas of lift/precipitation on either side of Connecticut. Consider this solution the 7-10 split.The best forcing along the mid level warm front takes place across Maine and the sea coast of New Hampshire while the best low level forcing occurs in a narrow band across Long Island and into Fairfield County and the Hudson River Valley along what is known as an inverted trough.

So, which solution is right?

Hard to say. The track and strength of the mid and upper level lows is impressive. There will be several bands of heavy snow nearby and the atmosphere is cold enough with a deep layer near -15c that any bands of snow that do develop could be quite heavy. Additionally, the wind will be impressive. The GFS model (shown below) shows a deep mixed layer with the potential for gusts up to 60 mph Sunday morning. This is likely a bit overdone.



The European model sort of splits the difference with a more “in the middle” solution. Not nearly as robust as the GFS and not nearly as paltry as the NAM. I think our snowfall map looks pretty good with 3″-6″ for most of Connecticut and 6″+ for northeastern areas. Let’s see how this one develops!


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