There are times when you look at a forecast and start to get concerned.  These are one of those times.

Let me first state this forecast is filled to the brim with volatility.  So much so that even the National Weather Service to wary of developments right now.  Are snowfall too low or too high?  Are current observations a trend or just an aberration?

Above is the water vapor satellite image with the strong Sub Tropical Disturbance charging to the east towards the Mid Atlantic coast.  First off the bat I'm sure you notice the intense lifting developing over much of the Mid Atlantic from southern New York down to North Carolina.  This lifting is expanding in size and intensity.  Further, and more interesting is that the upper level disturbance over the Tennessee River Valley has taken a slightly more negative orientation.  The shift isn't extreme, but it enough to force moisture up to New York City in the form of virga as seen in this radar image.

Why is this observation important?  Well this tells me the moisture transport has shifted further north than any model had suggested aside from the 12Z ECMWF that is the snowiest of all the models.

Next we have cold air slowly bleeding south with 925 MB and 850 MB temperatures falling all day.  The entire Philadelphia and New York City metropolitan areas are below freezing in snow growth areas.  There is no doubt that the atmosphere is cold enough to support snowfall except for one factor.  First, have you noticed all this moisture on the radar but not a drop or flake has reached any of the locations in the northern Mid Atlantic sane some sleet in Cape May County.  This is a sign of very dry air.  In fact, while temperatures are slowly falling through the 40's and into the 30's, dew points are still in the upper 10's to lower 20's for much of the region.  Now, the danger in the forecast for all you snow lovers is the boundary layer is NOT supportive of snow accumulation with these surface temperatures.  In fact, such an environment would lead to much of the snow fall as rain if temperatures stayed this warm.  However, we know cold air (22 degrees in Binghamton, New York) is sinking south and moving into the region.

Remember that lifting over Pennsylvania?  (see above for short memory retention)  That lifting is due to a strengthening thermal gradient in the mid and lower levels.  That rising air will help to drop temperatures this evening and should support temperatures falling into the lower to mid 30's, cold enough to support accumulating snow.  This aspect is one of the wild cards arguing against increasing snowfall totals by the way.

On the other hand, a factor that would support higher snowfall totals than even I have forecasted, and I'm pretty aggressive, is the potential for strong frontogenesis and intense mid level disturbances.  All one needs to do is see the snowfall rates to the northwest of the upper level low right now in southwestern Virginia and western North Carolina to see the potential here as the upper low passes to the southeast of coastal New Jersey.  This will have to be watched late tonight into tomorrow morning.

Considering what I have in front of me, I'm playing it safe and increasing snowfall totals slightly.  Given the rapidly cooling atmosphere at the mid levels, falling temperatures at the surface, and the fact that moisture is already further north than currently forecasted, I believe this forecast to be reasonable.