The statistical models have been suggesting the possibility of a secondary low pressure system developing off the coast along a cold frontal boundary. The deterministic models ( GFS, NAM) haven’t shown anything until today. The general trend has been for the secondary low to form too far north and east to give any significant snowfall to our area, but the models are showing a light coating.
Below are the current low pressure center possibilities, based on different GFS possibilities (“perturbations”). Most are somewhat north and east.
The afternoon run of the NAM just became available. QPF values for PHL are now over 0.5 inches water. The critical temperatures of the upper atmosphere are now not as warm as the earlier run from PHL and westward. Still slightly warm for dry snow—some sleet or ice pellets will mix in reducing snow totals. Approximately 3-5 inches possible for PHL and immediate west is the current call.
The afternoon model runs are not the best, since they don’t incorporate new radiosonde upper air data. (That’s those weather balloons.) Will have a better handle on snow totals with the evening runs. Will update by about 9:30 PM tonight.
