Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Friday Update & Weekend Update

Posted Friday 11/21/25 @ 10:21 AM — The ECMWF-AI model has led the way with a forecast of slower clearing on Saturday. Here’s the RRFS capturing the same forecast now—

I’ll post the full “Weekend Weather Forecast” later today.

Thursday and Weekend Preview

Posted Thursday 11/20/25 @ 10:06 AM — Today’s forecast remains unchanged. Mid-level clouds and light winds for much of the day. The RRFS shows some thinning clouds at times and even a break in the clouds mid to late afternoon in some areas.

Satellite image (clouds) with breaks and thinning to our west. (Click on image for a larger view.)
06z RRFS shows some breaks and even sunshine about 4 PM. Blue=low clouds, maroon=mid-level clouds, tan = high cirrus clouds (Click on image for a larger view.)

High near 50º in the city but just short of 50º in the northwest suburbs.

As for Friday night and Saturday morning, the trend is for much of the heavier rain to move to our south, missing our area. The ECMWF has joined the ECMWF-AI with clouds and some showers lingering into noon time, especially areas south and east of the city. Slow clearing except areas north and west. Sun breaks out by mid afternoon.

Sunday- sunny and milder.

Thursday and Weekend Outlook

Posted Wednesday 11/19/25 @ 7:18 PM — The system that brought us rain early Wednesday has left considerable low level moisture in its wake. Additional cloudiness is on tap for Thursday with somewhat milder temperatures. There may be areas that see breaks in the clouds Thursday mid to late afternoon. Seeing the sunset is a good possibility in many areas.

Another system approaching from the west will bring low clouds in again for Friday and rain by Friday evening.

18z ECMWF-AI forecast for Saturday afternoon. Definitely an outlier but can’t be ignored. Most models have the rain exiting by mid morning and clearing during the afternoon. (Click on image for a larger view.)

There’s uncertainty with the track and speed of this storm— the Canadian RGEM having most of the rain move to our south Friday night. The GFS, RRFS and several runs of the ECMWF-AI have the rain moving right over us.

Most models have the rain exiting by Saturday morning with clearing skies. Several runs of the ECMWF-AI show lingering rain and light showers into the afternoon.

The Sunday Marathon will have partly cloudy/partly sunny skies with highs in the low 50s.

Tue 5:35 PM —Forecast Review —The numerical weather models are impressive but today they let us down. I can’t find a single model that had forecast the ice pellets many areas saw about 3 PM this afternoon. The closest suggestion of any precipitation this afternoon was the 12z Canadian HRDPS—
12z HRDPS forecast precipitation probability at 3 PM today. Generally, pink-red (>20% on an hourly basis) is significant enough for some of precip. However, the model showed no actual precipitation and the precipitation type forecast was rain, not ice pellets. (Click on image for a larger view.)

Even the afternoon hourly HRRR and RRFS runs did not forecast this weather. Fascinating! Hopefully we won’t see any more surprises in the short term.

Tuesday Forecast Update

Posted Tuesday 11/18/25 @ 8:16 AM — Despite a rising barometer and clear skies this morning, the models are consistent in forecasting cloudiness moving in just before noon and mostly cloudy conditions by 1 PM.

While the approaching system will be to our south, recent model trends suggest the precipitation shield in our area will bring as much as 0.20′ to 0.40″ of rain by daybreak Wednesday. Rainfall increases from north to south.

Today’s 06z RRFS total rainfall forecast by Wednesday at 8 AM Thin black contours are labeled and are 0.20″ increments. (Click on image for a larger view.)

Wednesday looks dry, but fairly cloudy for much of the day.

Originally Posted Mon 11:09 AM —A general weather pattern where a dip in the jet stream over the eastern US with a ridge over the central US has persisted for many months. There’s no current sign of this changing. For those longing for cold snowy winters, I’m not sure this is the best setup for anything but light snow or mixed precipitation events at best.

GFS forecast for Wednesday morning. The dip in the jet flow (as captured by the red 500mb-1000mb thickness line) has been a feature for many months. Warmer air is staying in the central US while we are on the cooler side of things. There’s no current sign that this is changing. (Click on image for a larger view.)

One of the ‘side effects’ of the current pattern is that storms tend to form to our east, northeast or to our south. We are missing the heavier precipitation with these systems.

On Monday, a deep low northeast of Maine and associated pressure gradient will continue to bring gusty winds. Some instability cloudiness will develop again in the early afternoon today.

06z RRFS wind meteogram for Blue Bell, PA Winds subside on Tuesday and early Wednesday. (Click on image for a larger view.)

Our next weather maker is a low pressure system that will pass to our south Tuesday night into early Wednesday. We’ll be on the northern edge of the rain shield. Rainfall looks to be in the 0.20″ or possibly 0.30″ range at best.

Clouds for this system move in Tuesday around noon and rain moves in about 9 PM or so.

Reinforcing cooler air moves in for Wednesday with considerable instability cloudiness and some increase in wind speeds.

Another system with more clouds for Thursday and Friday will pass to our south. The rain with this system will likely miss us.