This morning’s models still show the upper air clipper low moving through our area Saturday morning.   The GFS has the system weakening as it approaches Philadelphia, with a QPF that is now about 0.06 inches water.   The NAM doesn’t weaken the system and maintains a QPF of about 0.11 inches water.

The light snow starts about daybreak and ends about noon.  Depending upon your model of choice and the expected high snow-water ratio of 15:1 or 20:1, we could get about 1-2 inches, but a mere coating is also possible.

I’ll update with tonight’s models.   The early NAM data becomes available as early as 9:15 PM

Fri 5 PM: This afternoon’s models have the very light snow starting a bit later and ending early afternoon.  The trend has been towards less QPF.   The experimental NBM (National Blend of Models) has a QPF of 0.06 for our area, or about about a coating to 1 inch of snow.

As mentioned, no big snowstorm for Saturday, but a clipper disturbance (an eddy current or area of vorticity) moving down from Canada in the northwest flow will bring the chance of light snow or snow showers to our area during the day on Saturday.

The GFS has a QPF of 0.14 while the NAM is lower at 0.06 inches water, a difference of a factor greater than two.  Those are big differences with small amounts- translating because of the extreme cold to a coating – 2 inches with a snow-water ratio extremely high at greater than 1:15.

That said, forecasting precipitation with clipper disturbances, especially when there are big differences between the GFS and NAM,  is tricky.   So, as usual, we’ll really have to wait until Friday evening to have an accurate handle.

Thurs noon update – QPF values have further decreased. Looking more like snow showers or a dusting of snow.

Thurs 6 PM update- QPF values are back to the levels from last night  0.15 GFS and 0.06 NAM.   Taking an average, we would have 1.5 inches of snow.   Still too early to tell for sure.