FRI 9PM UPDATE regarding JAN 3… RAIN to SNOW in VA M DEL WAV western NC se KY eastern TN

2100 est 12/31/21
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As I stated yesterday one of the key aspects to this potential SNOW event on Monday morning January 3rd is the development and the intensity of the second area of LOW pressure on the southern end of the cold front that comes through the East Coast on Sunday night -early Monday morning January 2nd into January 3rd. The various models have been going back and forth with the development and the intensity of this second LOW pressure area but now that we are getting closer to the event, there is more agreement with the various models here at midday on this Friday December 31.

The early morning 6z operational or regular GFS model which came out at 6am was showing a much weaker second area of LOW pressure on the cold front when it developed in Georgia late Sunday night. The result is a lot less snow because the weaker LOW pressure area pulls in less cold air from the north and the precipitation does not come down as hard. This was a change from what the GFS model is showing on Thursday.

However, at midday, the 12z GFS model did a reversal and is now very strong with the second LOW pressure area on Sunday night as it develops in Georgia and moves into the Carolinas. Moreover, other models such as the European and the Canadian have also turned stronger with the second LOW that forms on the front Sunday night into Monday morning in Georgia and South Carolina. In other words, we are moving towards model agreement which is what you want to see in the weather forecasting business.

This image shows the12z operational or regular GFS model as of midday on Friday. The super dark blue areas represent really heavy snow and if this was a normal winter with cold ground temps and the roads and other surfaces were not wet, then areas in central and eastern Virginia into the Delmarva would see 8 or 10 or maybe even 12 inches of snow from this system. But that is not what we are looking at and the wet ground and the warm ground temperatures are going to be a real inhibiting factor even if the operational or regular GFS model verifies exactly like it is showing today.

Next I present the operational or regular midday Canadian model. The reason why this is important is that the Canadian model has been downplaying the second LOW pressure idea for the past few days. But as you can see, it is now quite aggressive with the second LOW and looks very similar to what the GFS model is showing at midday on Friday. So that’s a step towards model consensus.

Next here is the 12z operational European model from Friday afternoon. It is also a bit strong with the second LOW and produces an area of snow in southwest Virginia, the mountains of western North Carolina, and northeast Tennessee and in central and eastern Virginia into the southern Delmarva.

Notice that there is a GAP in the accumulating snow area in the Virginia Piedmont. In fact, this Gap in the Virginia Piedmont area shows up on all of the models at midday.

What happens is that the initial burst of snow on the northwest side of the LOW in Georgia brings heavy Sunday night into early Monday morning in the mountains of western North Carolina, eastern Tennessee, southeast Kentucky, and southwest Virginia. But then as that LOW jumps to the coast, the moisture shuts off and it re- develops in central and eastern Virginia essentially bypassing much of the Virginia Piedmont. That is why the models were showing two areas of accumulating snow with a gap in between them where not much snow falls at all.

Finally based upon the latest trends in data it does not look like the moderate snow Monday morning will reach into Winchester / DC Baltimore / Philadelphia/ NYC. . There is a chance that the moderate now will get close to Washington DC and certainly impact the northern Virginia suburbs. This could be a case where locations such as Rockville, Bethesda, Ashburn and Winchester see a lot less snow than Manassas and Culpeper in Northern Virginia.

The temperatures on Monday morning will get down to 32 degrees on all the models during the height of the storm which is how and why the snow will accumulate on the normally colder services but not on the main roads — which will likely stay just wet because of their warm surface temperatures.

Once the event is over by midday Monday, temperatures will jump up to near 40° and much of the snow on these cold and services will melt especially the Sun comes out in the afternoon.

SPECIAL UPDATE 18Z FRIDAY OP GFS ….WOW
The 18z Operational GFS on this Friday evening is gangbusters. It’s actually even stronger than the 12z operational GFS and shows an incredible amount of heavy snow coming down in a very short. Of time…. probably within a 48-hour time window. I’m not sure but this might be the heaviest dark is color blue and snow signal that I’ve ever seen in Central and southeast Virginia from the operational GFS model. Notice also that the moderate snow at 7 a.m. on Monday Morning has reached Baltimore DC and even into Philadelphia and it’s still snowing as far back as the Virginia Kentucky border .

Not surprisingly the model has increased its actual snowfall amounts but again please keep in mind that this is based upon a regular 110 to 1 snow ratio with cold ground and dry conditions. The snow ratio for this event Monday morning will NOT be 10 to 1 and the ground will be wet and warm. That being said and numbers are a little higher and that is also the case with the 18z GFS ensemble’ that 18z GFS SNOW forecast seems like a pretty reasonable forecast if the 12 Z and the 18 Z operational GFS model turned out to be correct.

This image shows, that according to the 18z GF , it will be snowing in Raleigh and Greensboro as well as Richmond Williamsburg Tappahannock the Middle Peninsula Salisbury and Williamsburg at least until 12 noon on Monday and it might snow until the afternoon hours in Southeast Virginia and Northeast North Carolina !!! This is a bit of a surprise because the earlier data show the system would leave by midday and sky is clearing out which means temperatures would get close to 40 degrees and the snow would melt.

Of course maybe the18Z GFS has gone Bonkers but it’s something to keep in mind for future trends