However that's not the full story. Not only is the amount of precipitation unusually uncertain for NYC but the model members are unsure what side of the freezing line the temperatures should be. Here is another multi-panel image from the Penn State e-wall site showing the expected precipitation type and the location of the surface and 850 mb freezing line for the afternoon on Feb 08 (21 UTC).
Visualized another way is this SREF sounding plot below showing all the members plotted. All the members show that surface temperatures should be cold and likely from 30 to 40 F. That's unfortunately centered around freezing and the results are dramatic with respect to what kind of precipitation is expected to fall. The left panel shows a huge splatter of expected precipitation types in the late afternoon based on a partial thickness technique. Unfortunately changing the technique won't improve the uncertainty what will fall in the late afternoon for NYC.
|Forecast SREF profile of temperature (red) and dew point (green) for JFK valid for 2013 Feb 08 21 UTC. The left panel shows the expected precipitation type for each model run (red circles) based on the partial thickness technique.|
This forecast dilemma is not going to improve until we actually see the observations in the morning and see which side of the freezing line New York City will happen to reside. I'm going to be paying special attention to the AMDAR aircraft sounding profiles as they take off from the NYC area airports. Unfortunately I hear that flights are being canceled left and right in the NYC area just when we need frequent observations of temperature aloft. That's why frequent radiosonde launches will be so critical for the NYC area tomorrow. It's the only platform that can successfully get us the data we need in bad weather. That is unless some group can fly foul weather drones.
Now for the Boston area, there is more confidence of higher liquid equivalent precipitation though a couple model members leave Boston almost as dry as New York City. As for snowfall, there is also a similar uncertainty in temperatures but all the runs "safely" keep Boston below freezing throughout the atmosphere and snow, and lots of it, is a virtual certainty.
|Same kind of time trace for the SREF as above but for Boston, MA. Note the precipitation uncertainty is similar as fo|
|Same forecast model sounding for the SREF as above but for Boston, MA. The low-level temperature uncertainty appears just as high for BOS as for JFK but the soundingis colder and all members forecast snow.|