Reviewing last night’s models,  here are the trends– Cold air in the upper atmosphere moves in sooner and supports snow sooner, however the models still have the lower atmosphere at 40 degrees around midnight, so accumulating snow likely won’t occur earlier.

Precipitation (as rain)  starts earlier, now  in the late evening Wednesday.  With the  earlier chilling of the upper atmosphere, the transition from rain to snow may occur earlier (about 2 AM), BUT it will be a wet snow and warmer temps at the surface will greatly reduce early accumulations, especially around PHL.

Accumulating snow may not get going until 4AM or later and the accumulating snow will be ending about 8 AM.  

With  colder air moving in earlier in the upper atmosphere, the NAM’s “precipitable water” is less and  QPF values have reduced  to about 0.50 inches water.

What this all means is that total snow accumulations are looking lower at this time, especially in the immediate PHL area.  I’m thinking 3-4 inches around here, greater accumulations in the north and west.  It will be an icy and heavy accumulation.

Competing aspects of temperature and precipitable water values will make this storm accumulation forecast lower than usual confidence, but I’m leaning on the low side.

We won’t really know until tonight’s models.   Stay tuned.