Monthly Archives: December 2020

Philadelphia Area Weather Forecasts

ACTIVE WEATHER THROUGH SUNDAY

Thur 08:49 PM Update— Tonight’s models suggest any wintry precipitation on Sunday will be well north of the Philadephia area and suburbs.

An active weather pattern with a series of systems and fronts will affect the Philadelphia area from New Years Eve through Sunday.

Tonight (New Years Eve), a cold front will continue slip to our south. Additional showers broke out this afternoon, but no rain is expected this evening.

Thu 05:35 PM Update —Falling temperatures tonight may result in some black ice on roadways later tonight.

On Friday, the same front will slowly move back as a warm front, as low pressure moves up through the Great Lakes. Rain will return between 12 noon and 3 PM Friday and there may be some mixed sleet and freezing rain in the northern and suburbs. 

For Friday, freezing rain (red shading) is predicted by the NAM-NEST very far northwest, but it wouldn’t surprise me if it’s underestimating the wintry mix at the start and some sleet is falls closer to the city, north of the lavender line (upper level freezing) shown below—

NAM-NEST Precip type (red=freezing rain)  and upper air critical temps Friday 4 PM (Click on image for a larger view.)

Eventually, there will be a changeover to all rain even north of the city as the warm passes through.

Saturday features clearing and some sun. It will be unseasonably mild, with highs in the low to mid 50s.

Things get interesting Sunday, as the low pressure system near the Great Lakes spawns a coastal low off of Virginia—

GFS version 16 surface precip forecast 1 PM Sunday (Click on image for a larger view.)


Most models (and the model blend) have rain for our area on Sunday, but the latest “parallel GFS version 16” has greater low pressure intensification and more cold air on the northwest flank of the storm.

As a result, the new GFS version 16  is showing some snow and accumulation for Sunday afternoon north and west—

GFS snow depth forecast Sunday 3 PM  (Click on image for a larger view.)

 

The latest NAM and NAM-NEST and GEFS also show some snow falling far northwest, although not as much as the GFS.

Based on comparing predicted temps with actual temps, the new GFS is running a little too cold today, which may explain the higher wintry precip forecast.

I guess we’ll see how good the new GFS model is. Stay tuned.

Philadelphia Weather Outlook

NEW YEARS EVE & DAY WEATHER OUTLOOK

The weather for New Years Eve will dry, as a weak cold front is expected to move through with showers early Thursday morning and things dry out for New Years Eve. 

However a warm front associated with a low pressure system in the Midwest brings in rain New Years Day (Friday) to start out 2021.

The general pattern this week is for our area to be under the influence of an upper ridge pattern and a mild moist flow from the southwest ahead of this low pressure system moving up  to the west of us through the Great Lakes on Friday—

GFS (new version 16) forecast 2 PM Friday ; arrow represent upper flow  (Click on image for a larger view.)

After the rain moves out Friday night, Saturday should turn out dry and mild with high temps in the low to mid 50s.  I should mention that average temps are 41 º high,  25º low ( Blue Bell) this time of year. 

Yet another system moving in Sunday brings more rain as a coastal system tries to develop off the coast.  The upper air pattern does NOT favor development of a nor’easter or any snow from this system. 

In fact, snow lovers right now will have to wait for a pattern change. As mentioned in several posts recently, my pattern assessment is “lack of very cold air” to our north. 

NAVGEM Surface Temperature Forecast Jan 8- Warmer than average in polar areas and most notable are the warmer temperatures over Greenland. (Click on image for a larger view.)
Temperatures Departure from Average