Fri 07:37 AM Update — The next chance of snow for us (Monday evening into Tuesday) is about 96-108 hours in the future, still beyond the range of the short range, higher resolution  models.  (The shorter range, higher resolution models forecast 84-89 hours in advance at best. Many only forecast 48-60 hours in advance.)  

Current operational GFS snow totals by Tuesday afternoon—

GFS snow totals by Tuesday afternoon. (Click on image for a larger view.)

The above GFS snow totals are somewhat similar to the ECMWF (European), Canadian GEM-Gobal and German ICON.  Stay tuned.

Thank you to those of you who took part in my recent user feedback poll.  Here are the final results:

“Users, would you like  to see all  updates posted to Twitter or just the major new posts (as currently done)? “

With it so close, I’m going to stay with only posting major new posts to Twitter,  but with an occasional update also posting. (A slight change to the  current approach I use.)   The updates (such as those on this page) won’t be automatically posted to Twitter.

Thu 08:06 PM Update — Today’s GFS has joined other models (Canadian, European, ICON and GEFS)  in predicting about 1-3 inches of snow here Monday night into Tuesday morning. (Unfortunately, the newer GFS v16 has not been available today due to planned maintenance of NOAA’s servers.)

Current GFS snow totals for Tuesday 10 AM  (Click on image for a larger view.)


A new wrinkle for getting larger snow accumulation is going to be temperatures, which are trending somewhat warmer at certain levels of the atmosphere, especially near Philadelphia.  Many areas will have a sleet/rain mix at times during the event reducing snow totals and making an accurate snow total forecast difficult.   Since the storm is coming during the nighttime hours, a period of sleet or freezing rain is a possibility as temperatures near the ground may drop below freezing—

GFS Precipitation Type (PTYPE) Monday evening (Click on image for a larger view.)

A change back to snow is expected before ending Tuesday morning.

The fine structure of the thermal profile won’t be known until the day before the event.    Stay tuned.


From Wednesday …

Today, several people at work asked me, ‘so where’s the snow?’

The statistical ensemble (GEFS) model continues to forecast a minor snow possibility for the overnight period from Monday into Tuesday morning.  (see yesterday’s post for the precip forecast graphic; it hasn’t changed much with today’s model runs.)

The sort of thing I like to do is compare the soon-to-be-released GFS model version 16 and the current operational GFS model (version 15.2)’

(The GFS 16 is scheduled to become the operational model the first week in February.)

The soon-to-be-released GFS 16 has  significant snowfall for our area, 4-7 inches—

GFS v 16 precip rate forecast for Tuesday 7 AM   (Click on image for a larger view.)


The current operational GFS model has the storm a bust with little development and little snow—

GFS (current operational) forecast Tuesday 7 AM (Click on image for a larger view.)


The current Canadian Global and the European models are closer to the the low end with some snow 1-2 inches.

In the time period in question (~138 hours in the future), the statistical GEFS model is probably the one to consider most—

GEFS snow totals Tuesday morning  (Click on image for a larger view.)


If that’s the case, the soon-to-be-released GFS model v16 has a serious precipitation over-prediction bias. 

The fun of this is to see what happens.   Stay tuned.