Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Accumulating Snow Likely Saturday night

Updated Friday 12/12/25 @ 10:07 AM — The latest Model Blend shows an increasingly likely snowfall for Saturday evening and night. Here’s the current blend mean snow accumulation—

Today’s NBM mean snow accumulation (Click on image for larger view.)


Light snow moves in about 9 PM from the northwest and tapers off early Sunday afternoon. It would surprise me if the totals are slightly higher

Possible Snow Saturday Night

Updated Thursday 12/11/25 @ 11:25 AM — Recent runs of several models have converged on a forecast for accumulating snow Saturday night ending Sunday morning.

ECMWF-AI total snowfall Sunday morning. (Click on image for larger view)

A cold front approaches Saturday evening. Low pressure is predicted to form along the front and temperatures which start out above freezing will dip below 32° as the low intensifies. About 0.25” water equivalent will fall either as wet snow, sleet, then changing to all snow before ending Sunday morning. Due to the temperature transition and the intensification, exact snow totals will be difficult to nail down at this time but 1-3” is looking very possible.

New US AI weather model becomes Operational

Updated Wednesday 12/10/25 @ 7:22 AM — Yesterday, NOAA announced the operational release of three AI weather models, to become available December 17th. Named the AIGFS, the AIGEFS and the HGEFS, these are models are based on the Google DeepMind Graphcast AI engine and draw on the same forecast historical database as the ECMWF-AI model. (These models have been recently available on AWS, but with a 16 hour delay.). The release version should become quite useful for forecasting and the HGEFS is a hybrid ensemble version should be especially useful when available realtime and compared to same runs of other models.

These models join the European AI model and the Canadian AI “spectrally-nudged “models for a new direction in forecasting.

Unfortunately, the the AIGFS and the other new models have limited parameters compared to the Canadian and European models.

Wednesday Light Rain and Outlook

Posted Tuesday 12/09/25 @ 4:24 PM — An approaching cold front will bring light rain on Wednesday. Rain begins late morning, perhaps as late as noon which will allow temperatures to rise above freezing. No frozen precipitation in our area is expected.

This is a fast moving system and any light rain will end by 7 PM. Less than a quarter of an inch of rain is expected, with rainfall totals decreasing from west to east.

Thursday looks dry and cold with some cloudiness, especially western sections, early afternoon.

Some light precipitation Friday into Saturday morning looks possible, but amounts are looking minimal.

The next chance of any light snow may be late afternoon Sunday into Monday morning. The ECMW-AI is showing a range 1.5″ and the Model Blend (NBM) about 3.5″. Of course, it’s way too early to hang our hat on this forecast.

18z ECMWF-AI forecast snow accumulation by 1 AM Monday morning. (Click on image for a larger view.)

Some family responsibilities may keep my regular posts and updates less frequent over the next couple of weeks.

Tuesday

Updated Monday 12/08/25 @ 9:18 PM — Watching the Eagles and “doing the weather”. Cold tonight!

NBM low temps

Tuesday will have more sun and much less wind than today. Mid level clouds similar to today around noon followed by sun again.

Wednesday’s light precipitation will likely occur after later than first forecast, meaning light rain

Originally Posted Sun 4:42 PM —This week’s weather highlights will be occurring about every two days.

First, a cold front, now in northwestern PA will move through our area slightly after midnight tonight (Sunday). Very cold air will move in behind this front with windy conditions, especially Monday morning. High temperatures on Monday will remain below 32º with wind chills near 20º

For Wednesday, a storm system will move to our north. While there will be cold air aloft, the northern track of this system will bring in milder air, likely changing any frozen precipitation to a mix or changeover to rain.

12z ECMWF-AI forecast for Wednesday at 2 PM. Cold air aloft (red, lavender contours) and warmer air near the surface (yellow contour and white 32º line) will allow a mix of sleet and perhaps some snow, possibly changing to all rain. (Click on image for a larger view.)

Another thrust of cold air moves in behind this system, in time for the next system to approach Friday night into Saturday—

12z ECMWF-AI forecast for Saturday at 7 AM. Again, colder air loft with above freezing temperatures near the ground will allow for sleet possibly mixed with wet snow. Some accumulation may be possible at the onset. (Click on image for a larger view.)

Right now, the colder than seasonal average pattern looks to continue into following week. No major snow or rain storms are forecast at this time.