WEATHER OUTLOOK

Reviewing the major models, at this time, it appears that the balance of December won’t have a pattern for snow in Philadelphia.

Short duration dips in the jet stream will bring cold periods, but moisture flow from the southwest will make these colder periods of moderate duration, allowing wet and mild weather to return along with deep storms whose tracks will be moving to our west instead of along the coast.

Today’s (Sunday) GFS and FV3-GFS differ significantly in the very long range with these similar models having very different forecasts by New Years Eve.

For this week— A storm for Friday is a now posing to be a significant rain storm and the storm potential mentioned for Sunday into Monday also appears to be wet instead of white.

The chance of seeing a white Christmas here have faded, at least for now.

The global models show very frigid air building in the polar region, Siberia and Greenland during the last week in December. A shift to much colder weather and stormer conditions (snow) is expected by the end of December into the first week of January.

WEEKEND WEATHER FORECAST

The forecast for rain on Saturday through Sunday still stands. A closed upper low pressure system in the southeast will spawn two low pressure systems that move up over Philadelphia this weekend.  The upper low will move up over our area on Sunday.

One change has occurred with the forecast— The rain on Sunday is expected to be heavier than the rain on Saturday.  In fact, the lowest QPF is likely during Saturday afternoon.

Saturday will be cloudy with rain. The rain may become light and intermittent in the afternoon.  High 55 49.

As the upper low moves over our area on Sunday, there will be increased chances of rain, possibly heavy Sunday.  The upper low will result in colder temperatures. High 47 42.

Long Term Outlook- Updated Saturday 5 PM
Reviewing the major models, at this time, it appears that the balance of December doesn’t have a pattern for snow in Philadelphia.

Short duration dips in the jet stream will bring cold periods, but moisture flow from the southwest will make these colder periods short-lived,  allowing wet and mild weather from deep storms whose tracks will be moving to our west instead of along the coast.

A storm for Friday is a now posing to be a significant rain storm and the storm potential mentioned for Sunday also appears to be wet instead of white.

The chance of seeing a white Christmas here have faded, at least for now.

The global models show very frigid air building in the polar region, Siberia and Greenland during the last week in December. A shift to much colder weather couldn’t be far behind.

WEEKEND WEATHER OUTLOOK – THURSDAY EDITION

The GFS, FV3-GFS,  NBM and NAM models have all come to a consensus that this will be a rainy weekend in Philadelphia.

All models have rain for both Saturday and Sunday! (Sunday afternoon is expected to have the least amount of rain. )   The GFS from earlier this week seems to have had the best continuity with the forecast and seems to have been more accurate than the new, still unofficial, FV3-GFS.

Saturday: Cloudy with rain. High 50-55

Sunday: Cloudy with rain in the morning, intermittent showers in the afternoon.   Breezy. High near 50.

The models have been consistent over the past week in predicting a large storm for Dec 24th, Christmas eve. It looks like rain for our area, but there’s a reasonable chance of light snow or flurries early Christmas morning as very cold air moves in behind the low pressure system.

WEEKEND WEATHER OUTLOOK

Wednesday Evening Update
Tonight’s NAM has joined the GFS in predicting rain for much of Saturday and Saturday night. The GFS continues with some showers continuing on Sunday.
The still unofficial FV3-GFS is more optimistic for Saturday evening and Sunday, as it keeps this precipitation to our south. Too early to tell.

The [relative] warm-up mentioned in my posting last week is on track to arrive late Friday.   Unfortunately, the milder temperatures will be accompanied by low pressure and rain.

The low pressure system arriving late Friday will be interacting with a cut-off air upper low in the southeast.  Much of the heavier rain will be Friday night and it may taper on Saturday.

There’s much uncertainty with the specifics and timing of this rain, because interactions with upper closed lows are difficult to model.

There’s some suggestion that the upper low may spawn another low pressure system for part of Sunday.  Too soon to tell.

Milder temperatures will persist into next week, with a bit of a roller coaster effect as cold air dips in several times.  It will be milder, then a day or so of cold, then milder again.

Real changes back to winter are forecast to occur around Christmas Eve with a large storm and deep cold returning.