The model depiction of the small low pressure system expected to affect us on Thursday night into Friday continues to evolve.  The NAM and GFS differ on timing and coastal development.  The GFS has a more substantial coastal storm developing on Friday and coming very close to PHL, but the heasiest precipitation shield still misses us.

It should be noted that the degree of coastal development and the degree of upper air troughing continues to change, with the trends leaning to the possibility of more snow than the currently expected 1 to 2 inches.

Put another way, it wouldn’t take much change for the snow in our area to be more significant.  It also wouldn’t take much change for it to be just a period of snow showers.

To give perspective on the model’s continuity, tonight’s rainfall, originally expected to be quite heavy, doesn’t appear that it will be be very significant.  So confidence in the forecast for Friday continues to be lower than usual.

11 pm –tonight’s GFS has increased the QPF to 0.33 inches water. The NAM has reduced it to 0.07.  Large model differences!