Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Sun 5:10 PM —Forecast Review —Some very light showers have moved through western Chester/Montgomery counties and reached into Philadelphia. Closer to the RRFS forecast than the HRRR or ECMWF.

The dynamics are unfavorable right now over Philadelphia to support much in the way of rainfall. However, things change by about 10 PM to midnight where some heavy rain and storms may move in.

Sunday Forecast Update

Posted Sunday 08/02/26 @ 8:35 AM — Today’s forecast is mostly unchanged. The uncertainty centers around the timing of the onset of the showers and thundershowers expected to move in either mid to late this afternoon or this evening. The best match for the current radar is the ECMWF—

Current radar around 8 AM with water vapor image and RAP model Omega. Few models capture this breakout of showers. (Click on image for a larger view.)

If we were go all in on the ECMWF, it would imply that most of the daylight hours are precipitation free in the immediate Philadelphia area.

The latest REFS (combines the RRFS and the HRRR) shows some showers just west of Philadelphia in the late afternoon—

06z REFS rain plus standard deviation (contours) at 6 PM Sunday. (Click on image for a larger view.)

A mix of clouds with breaks of sun this morning with mostly cloudy skies for this afternoon. Despite my earlier forecasts of showers increasingly earlier this afternoon, if we take the ECMWF and REFS together, the earliest we’ll see showers (west of Philadelphia) will be 5-6 PM and more likely closer to 11 PM. The earlier start is a low confidence forecast, but the 07z NBM seems to support it—

07z NBM forecast 1 hour precipitation at 5 PM. (Click on image for a larger view.)
Forecast Update

Posted Saturday 08/01/26 @ 10:13 AM — I mentioned that Saturday would have sunshine through thin high clouds in the morning. That dimmed sunshine is also due to smoke throughout the atmosphere above us (not so much at ground level).

12z HRRR smoke model showing Vertically integrated smoke total at this time. (Click on image for a larger view.)

A flow of increasingly humid air will affect our weather over the coming days. A warm front associated with a low will slowly move towards us this weekend—

Water Vapor image at XX with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , GFS potential vorticity contours (violet fine contours) with MRMS Radar and surface wind barbs, I’ve drawn the approximate position of the warm front. (Click on image for a larger view.)

Saturday‘s forecast remains on track with increasing periods of sunshine through mid and high level clouds.

The trend I identified with Sunday‘s forecast continues with the rain and showers moving in earlier with each successive model run. The latest RRFS from 06z shows showers (and thunderstorms) possible as early as 3-4 PM. The 12z model (not yet completed) suggests it may even be earlier.

06z RRFS forecast for 4 PM Sunday- 1 hour rain plus simulated radar. The orange contour is the general location of the northern edge of the heat dome. (Click on image for a larger view.)
Saturday – Sunday Forecast

Posted Friday 07/31/26 @ 7:41 PM —

Saturday

Saturday looks to be mostly sunny in the morning with increasing thin high level cirrus clouds towards late morning as a warm front slowly approaches. Saturday afternoon looks to have variable amounts of sunshine through high and mid level clouds. A few areas, especially near Trenton, may have showers pop up late afternoon; most areas dry.

Highs (Model Blend): Blue Bell- 88º Philadelphia 88º ±2.0º Average sd and confidence.

Sunday

Considerable cloudiness. A few isolated showers possible during the early afternoon: most areas dry. The trend noted this morning continues. Warm air and associated showers/thunderstorms move in early evening on Sunday from the south. Arrival about 6-7 PM with a few areas seeing some isolated showers around 4-5 PM.

Highs (Model Blend): Blue Bell- 88 º Philadelphia 87º ± 2.3º
Lower than average sd and higher confidence .

18z RRFS forecast for 7 PM Sunday. Rain and simulated radar. Orange contour is the edge of the heat dome. (Click on image for a larger view.)
Early Outlook Edition

Originally Posted Fri 9:42 AM —A warm front to our south will slowly push north towards us over the weekend.

Saturday will be sunny with some high cirrus clouds moving in during the early afternoon with some mid-level cloudiness at times towards late afternoon. A few highly isolated pop-up showers are possible, mostly in northern Delaware and parts of NJ. Most of the area will be dry.

As the warm front moves closer on Sunday, showers will break out but the majority of the models (ECMWF-AI and RRFS, CMC-RDPS) have these showers in Lancaster and Berks counties and westward. This morning’s 06z GFS does have a few showers in the immediately Philadelphia area late afternoon Sunday and early evening. This is supported by the AIGFS and the Hybrid AI GFS. Looking at the model trends, there is some indication that the system will advance somewhat faster, supporting the GFS forecast.

06z GFS forecast for Sunday at 7 PM. Rain and simulated Radar. Orange contour is the edge of the heat dome. (Click on image for a larger view.)

I’ll update later this afternoon or early evening.