Latest NAM model has rolled out.  Extraordinary amounts of QPF ( 2.34  inches water)  falling as snow.  The NAM has been remarkably consistent with these high amounts and I’m thinking that at least 24 inches of snow and likely 25-30 inches will be final amounts.  

I know I’m well above the official forecast snow totals, but as I said on my earlier post today, the NWS tends to ignore the NAM model for snow amounts, preferring the various global models like the GFS and the ECMWF.    In the past decade, when they’ve underestimated snow totals, it’s seems like they have always  ignored the NAM model.  (Similarly, last year’s fizzled “blizzard”, where they were predicting a monster storm this same week in January,  was correctly modeled by the NAM and incorrectly by the GFS and European models. )

So despite the tendency for the NAM to run a bit high in QPF, I’m sticking with the extraordinary QPF of the NAM for this storm.

Other changes suggest a little heavier and early start for the snow tonight.  So while things were looking closer to a 10 PM start, the HRRR (based on the NAM model) shows snow starting in Philadephia as early as 7-8 PM.

Sustained winds, around noon tomorrow, may be as high as 32 mph with higher gusts.  We likely will be close or reach the true definition of blizzard conditions.

Last night’s 1 AM models continue with the major snow storm  for Philly. Both models have  snow  starting earlier tonight (Fri), with snow starting as early as 7-8 PM, with  a few inches by midnight.

As is often the case, there are some differences between the NAM and the GFS models, with the NAM QPF  up to 2 inches of water and the GFS a bit lower than its previous run at 1.40 inches water.

In past storms, the average QPF between the NAM and GFS has worked.   That would still bring us into the 20-25 inches range for snow.

People ask me two things on the blog:  why don’t I quote the ECMWF more?  ….and why do I talk about the NAM model when no else does for winter storms?

Regarding the ECMWF (European Model), it is subscription only.   We’re talking big bucks for their data. They only provide certain data for free and QPF isn’t one of them.    If you read the NWS forecast discussions, the ECMWF hasn’t been all that great this season, so I’m not missing much.  (It was the ECMWF that gave us that “fizzled blizzard” last winter.)

As far the NAM, for some reason, maybe political, the mesoscale modeling branch of the NWS, which runs the NAM model,  isn’t taken  too seriously for winter season storms by the global forecast modeling branch of the NWS.

That said, after years of doing these forecasts,  I find the NAM can be remarkably good about rain/snow lines and even larger-than-predicted snowfalls.    Where the NAM goes wrong is overestimating  the QPF several days in advance.  But we’re getting into the timeframe where the NAM data is very useful.