Dan McQuade from Philadelphia Magazine Online interviewed me on Saturday about the big snow storm.

Read about it at:

http://www.phillymag.com/news/2016/01/25/philly-dentist-predicted-blizzard-jonas/

There are many past winter storms where there have been large differences between the GFS and NAM models regarding QPF (amount of precip).

By definition ( if not by other measures) tomorrow’s rain is not a winter storm, but the models differ significantly with the amount of precipitation forecast.  The NAM has been advertising 2 inches of rain for PHL, while the GFS has a light rain, less than 0.50 inches total.  That’s a giant difference.

When dealing with snowfall, the differences are obvious when a heavy precip forecast goes bust.   It will be interesting to see if the NAM or the GFS model verifies tomorrow.   Something to consider for later in the season when we likely see divergence in forecasts.

An interesting scenario coming up, with moisture remnants of previous hurricane Patricia move up as a extratropical  everyday low pressure system.

There are big differences in the models here, with the GFS cranking out an inch or more of (much needed) rain, but with the NAM model having  the moisture and heavy rain missing us and moving to our west.   The NAM has high pressure blocking the rain and keeping the low pressure to our west.

With the NWS and TV forecasters predicting heavy rain for Wednesday, this will be a good test of the NAM vs GFS models for precipitation in the upcoming winter.    In such similar discrepancies last winter, the drier NAM model was the winner.   We’ll see.