Winter Storm Outlook

MORE ACTIVE WEATHER

Wed 09:41 PM Update — As mentioned earlier, this possible snow event will be in two parts, a warm front type snow as early as Sunday followed by a secondary coastal low. The time frame is beyond the forecast horizon of the shorter range high resolution models.

FYI: The newer model runs of the major global models, the GEFS, CMC, and the ECMWF don’t become available until well after midnight. (The GFS model data for this forecast time frame becomes available about 11:10. ) Your favorite TV weather entertainer won’t have any meaningful updated forecast information this evening.

I’ll update tomorrow morning.

Wed 05:58 PM Update —There’s still much uncertainty regarding the amount of development and track of the secondary low late Sunday into Monday. Just about every model has some snow.  The latest European model is much slower with the development but brings a major snowfall to our area, especially areas just west of Philadelphia as late as Tuesday.   It’s way too early to post specific numbers.  Recent storm forecasts have over-stated the snowfall totals this many days in advance.  (The actual storm is well past the 84-89 hour range of the higher resolution models.)   But stay tuned.

BTW,  I saw this interesting article in the Washington Post.  

from earlier…

Cold air has built up in Canada and it will make its plunge into the eastern US over the next few days resulting in an amplified jet stream.

After several frigid days through Saturday, low pressure in the Midwest will try to bring warm air and moisture over us aloft (basically a warm front) on Sunday.  This should result in snow for us some time on Sunday afternoon or evening.   These scenarios (warm advection snows) can produce an inch or two of snow, sometimes more.

Of interest, several models have this Midwest low pressure system spawning a secondary coastal low late Sunday night—

GEFS model showing coastal secondary low formation Sunday night. (Click on image for a larger view.)

Depending upon the exact location of this secondary low, we could get additional snow.  Right now, the dip in the jet flow does NOT show an ideal track for development needed for heavy snow in our immediate area—

GFS model 300 mb jet stream flow. The dip isn’t sharp enough to bring the developing coastal storm close enough for heavy snow in Philadelphia.  (Click on image for a larger view.)


As we saw with today’s system, model storm forecasts several days in advance can easily change.  (The southward impulse (white arrow)  could phase more, causing a sharper bend in the flow.)   This one looks like it has potential, but the trend over the past day has been for a more eastward track.  

However, of interest is the German ICON model whose current forecast extends to 120 hours (Monday 1 AM).  It has very heavy snow tracking just south of our area late Sunday—

ICON model Snow Precipitation Rate Monday 1AM  (Click on image for a larger view.)

 

Using some new software, here’s the GFS projected snow totals for this potential storm—

GFS projected snow totals  (Click on image for a larger view.)

 

Stay tuned.