ChescoWx

From Meteorologist Bobby Martrich on these huge changes to Friday "Last 4 runs of the GFS are comical... and it's not alone with this idea of a colder day Friday - just after Christmas. Much colder in fact, so instead of 50s you cut 25° off the high temps and get frozen precip, not rain. This goes back to the prior video discussions where I talked about models struggling in seasonal transition and being overzealous about the supposed "torch" pattern. If you're on the colder side of that thermal gradient, it's a much different outcome. This is the result of models completely whiffing on the extent of blocking in the Northern Atlantic and Atlantic Canada and a much stronger Quebec high providing the cold air damming. While we need to see this apparent trend to continue to alter the forecast, the Friday forecast could look much different if it does."

How's that high in the 50's you bet on for Christmas Day looking? LOL!!

The latest European for Friday.....a wee bit different from prior model runs.

Below normal temperatures look to continue through at least Christmas with some models now hinting at significantly colder weather than currently forecast for Friday. We do have a chance of some light snow, sleet and freezing rain arriving tomorrow morning. While amounts will be light the timing near rush hour could be a potential problem. We should dry out by tomorrow afternoon. Christmas Eve Day looks sunny. Plenty of uncertainty regarding both temperatures and precipitation by Christmas Day and Boxing Day.

Below normal temperatures look to continue through at least Christmas with some models now hinting at significantly colder weather than currently forecast for Friday. We do have a chance of some light snow, sleet and freezing rain arriving tomorrow morning. While amounts will be light the timing near rush hour could be a potential problem. We should dry out by tomorrow afternoon. Christmas Eve Day looks sunny. Plenty of uncertainty regarding both temperatures and precipitation by Christmas Day and Boxing Day.

I suspect that high near 57 on Friday will be coming down significantly later today...

06z GFS

This may be the largest temperature swing over 1 run I have ever seen on a model. The other models have similar cold trends.

Below are my obs from Thorndale in December 1998 and from the Coatesville 2W NWS observer. Not too much snow but just enough for the White Christmas

Happy first day of Winter to those that celebrate! We are at about our high temperatures for today with a cold front passing through this morning. Today’s temperatures will drop to freezing by evening. Below normal temperatures tomorrow with near normal high temperatures through Christmas Day. The warmest day of Christmas week looks to be on Boxing Day with temperatures well into the 40's and maybe even 50 in some valley locations. We turn chilly again on Saturday. It looks increasingly likely that snow will arrive by Tuesday morning's rush hour. We should see less than an inch of snow before any change to rain for most of the area with more up toward the Lehigh Valley. Additional rain shower chances for both Christmas and Friday.

Happy first day of Winter to those that celebrate! We are at about our high temperatures for today with a cold front passing through this morning. Today’s temperatures will drop to freezing by evening. Below normal temperatures tomorrow with near normal high temperatures through Christmas Day. The warmest day of Christmas week looks to be on Boxing Day with temperatures well into the 40's and maybe even 50 in some valley locations. We turn chilly again on Saturday. It looks increasingly likely that snow will arrive by Tuesday morning's rush hour. We should see less than an inch of snow before any change to rain for most of the area with more up toward the Lehigh Valley. Additional rain shower chances for both Christmas and Friday.

A return to chillier weather today with highs in the mid-40's. We stay below normal through Monday with maybe some wet snow arriving toward Tuesday morning. This should turn to rain pretty quickly from SW To NE across the area. Temperatures look to be near normal for Christmas Eve Day before we rise to about 4 degrees above normal for Christmas Day. Boxing Day looks to be the warmest day of the week before we cool down as we move toward the New Year's holiday.

A return to chillier weather today with highs in the mid-40's. We stay below normal through Monday with maybe some wet snow arriving toward Tuesday morning. This should turn to rain pretty quickly from SW To NE across the area. Temperatures look to be near normal for Christmas Eve Day before we rise to about 4 degrees above normal for Christmas Day. Boxing Day looks to be the warmest day of the week before we cool down as we move toward the New Year's holiday.

Over 0.50" of rain has already fallen here in East Nantmeal with as much as another 0.50" possible for some areas. We have already reached out high for the day of 56.6 just before 6am. Temperatures have fallen over 6 degrees since then and will continue to fall into the 30's by 4pm and freezing by 6pm. Lows tonight will fall to near 20 degrees and highs tomorrow only in the mid-30's. Temperatures will be near normal in the low 40's pm Sunday before falling back to below normal levels through Christmas Eve day. There is a chance of some snow by Tuesday morning that could be mixed with rain further south across the area.

Over 0.50" of rain has already fallen here in East Nantmeal with as much as another 0.50" possible for some areas. We have already reached our high for the day of 56.6 just before 6am. Temperatures have fallen over 6 degrees since then and will continue to fall into the 30's by 4pm and freezing by 6pm. Lows tonight will fall to near 20 degrees and highs tomorrow only in the mid-30's. Temperatures will be near normal in the low 40's pm Sunday before falling back to below normal levels through Christmas Eve day. There is a chance of some snow by Tuesday morning that could be mixed with rain further south across the area.