Daily Archives: Friday, October 24, 2025 8:18 pm

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Posted Saturday 10/25/25 @ 10:13 AM — The latest RRFS model shows an area of cloudiness moving in from the southwest between 2 and 4 PM this afternoon. This dissipates at night.

I’m still trying to get a handle on the possible storminess next week. One technique is to compare current water vapor with the model position of the upper level low. Here’s the water vapor current upper low position—

Current Water Vapor with “X” in center of upper low circulation. The distance to Philadelphia is about 1540 miles. On several models, that distance is showing at 1340 miles, meaning that the models are too far east with the current position. That calls into question the rest of the current batch of model forecasts.

The distance of the center to Philadelphia is about 1540 miles. On several models, the current distance is showing at ~ 1340 miles, meaning that the models are too far east with the forecast current position. That calls into question the rest of the forecast for the current run of models.
The latest ECMWF-AI model has moderate rain on Halloween, but with the current model in question, we likely know that this forecast is probably not correct. The latest available GFS-AI has most of the rain moving to our south, missing us!

Latest ECMWF-AI model (06z) forecast for Friday evening at 8 PM. Likely not correct. (Click on image for a larger view.)

So, the current models are providing an unusually low confidence forecast for next week.

Originally Posted Fri 8:18 PM —High pressure will give us dry weather this weekend with mostly sunny skies. Just very nice and seasonably cool. There’s not much else to say about this weekend’s weather. (Earlier model runs showed cloudiness for Sunday; that’s no longer the case.)

Current water vapor image captures the key elements for this weekend and the upcoming week and the caption explains key elements—

Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. High pressure over the northeast with a northwesterly wind flow. The white box shows an area of energy and potential vorticity that will spawn at least one and likely two additional low pressure disturbances for next week. The white arrows shows the track of the first disturbance which now looks like it will track south of our area, missing us. (Click on image for a larger view.)

The main take away from this post should be the word uncertainty in the forecast past this weekend. Indeed, I’ve rarely seen so little agreement among models and even a lack of continuity between successive model runs.

I wish I could hang my hat on any one model or even any one or two AI models, but it can’t be done. There’s even large differences between the GFS and the GFS-AI model, as well as between the ECMWF and the ECMWF-AI model. The differences boil down to the very basics: location of storm formation, the track, timing and speed.

As regular readers know, I’ve often remarked that the presence of a tropical system (Melissa, in this case) seems to confound the model forecasts. But the shear lack of any clear forecast seems to go beyond the presence of Melissa. So, right now, we may get heavy rain, or we may get next to nothing, it might develop as early as Wednesday or as late as Friday.

The ECMWF Ensemble (a statistical version) captures the extreme large standard deviation of possible forecasts.

12z ECMWF-Ensemble surface pressure with standard deviation (color) forecast for next Thursday shows the extremely wide range of high standard deviations (white area with red center) where low pressure my move or develop. With standard deviations in surface pressure of 14 mb far from the storm mean center, it doesn’t get much more uncertain. (Click on image for a larger view.)