Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Posted Sunday 09/21/25 @ 11:41 AM —We have sunshine through mid level and high clouds this morning as the models have vacillated back and forth over recent days with this forecast. Current satellite image shows the heavier cloud cover in central PA (as predicted), but erosion of clouds as they move towards us.

11:30 AM visible satellite with superimposed HRRR 3 hour pressure tendency (yellow contours) Back in my youth, this negative pressure tendency in the morning (that was all the data I had back then) would suggest little in the way of clearing. But, clearing in the afternoon is what the vast majority of the models area showing. (Click on image for a larger view.)

Posted Saturday 09/20/25 @ 10:08 AM — The RRFS and GFS show considerable cloudiness Sunday morning for our area. The RRFS has the cloudiness thinning out about 12-3 PM with sunshine through high cirrus clouds. I’ve gone back and forth on this cloud cover forecast with the experimental RRFS having been an outlier. That said, I’ve been using the RRFS quite a bit and its cloud cover forecasts have been impressive.

06z RRFS cloud forecast for 1 PM Sunday ( Blue=low clouds, maroon=mid-level clouds, tan = high cirrus clouds) (Click on image for a larger view.)

Posted Friday 09/19/25 @ 3:53 PM — Today’s models have backed off considerably on the cloudiness forecast for Sunday. The current trend is for some clouds in the morning, then mostly sunny in the afternoon. An exception to this forecast is the RRFS which maintains significant cloudiness. I’m leaning towards the sunnier forecast, supported by the ECMWF-AI model

Models guiding this forecast: ECMWF-AI, GDPS-AI, NBM, RRFS , REFS, RGEM , NAM-NEST

Originally Posted Fri 9:22 AM —High pressure over us on Friday will consolidate with high pressure to our north on Saturday resulting in a cooler, easterly flow of air for our area.

Current water vapor shows high pressure and a disturbance near the Great Lakes, associated with the short wave that move through on Sunday.

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. Water Vapor Imagery reveals emitted water vapor infrared TEMPERATURE,not reflected light from clouds. (Click on image for a larger view.)

On Sunday, an upper air trough (short wave) will move over us bringing considerable cloudiness and even the chance of scattered, isolated showers (according to the latest Canadian GEM model, but the latest RRFS has even less cloudiness and no showers. ). Diminishing cloudiness later in the afternoon as the wave move off to our east.

06z NAEFS with upper trough (white dash) and red contours 250mb heights that shows the ‘wave’ in the upper flow. (Click on image for a larger view.)

The thicker cloud deck will be in the far western suburbs and at the shore.

Saturday Forecast

Sunny and somewhat breezy/windy.

NBM high temperatures: Blue Bell, PA 76º Philadelphia, PA 78º
Higher than average uncertainty (based on standard deviation): ± 2.4º

Sunday Forecast

Updated Friday 09/19/25 @ 3:53 PM —Cloudy in the morning, especially far western suburbs. Isolated light showers possible. Mostly sunny by the afternoon.

NBM high temperatures: Blue Bell, PA 74º Philadelphia, PA75º
High uncertainty (based on standard deviation): ± 3.5º