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1) Surface features are somewhat farther to the east.
2) 500 mb: 1 vort max as opposed to 2, and somewhat farther south
It is still too soon to say whether the NAM is continuing to trend toward the model consensus that is to its east. Right now, the big cities from DCA to BOS are in line for accumulating snow but changeover issues should not be ignored. That risk still exists. Nonetheless, a significant snowfall of 6" or more should not be ruled out either.
My view remains the same as it has been for the past two days (see my February 27-March 12 pattern discussion from Friday): high risk of 4" or more in PHL, NYC, BOS and moderate risk of 4" or more in DCA. Amounts could be higher depending on the track of the storm.
Given the EC/EC ensembles/GFS ensembles/model consensus and the experience concerning historic blocks (-5.500 or below), the situation strongly favors a coastal/offshore track. The 12z GFS is also consistent yet again with this general idea. I remain somewhat concerned about the NAM but my confidence in it is somewhat reduced somewhat by recurrent initialization issues. However, such issues are not sufficient reason to throw out the NAM altogether and might be just minor in nature.
All said, in my view, the mostly snow (67% or more of precip. in the form of snow) scenario is probably more likely than the mostly rain one (67% or more of precip. in the form of rain). However, the mixing/changeover issue are real for the big cities. In conclusion, DCA to BOS will add to their monthly snow totals. The only real question that remains is by how much. For me, I'll probably wait until the 0z runs to make a detailed estimate given the continuing uncertainty and my concern regarding the NAM.
