Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Mon 10:00 AM —Forecast Review — Last evening’s late posting showed major differences in forecasting between the HRRR & NAM-NEST model forecasts and the new, soon to be released (I hope), RRFS experimental model. (RRFS– Rapid Refresh Forecast System, an hourly updated model with the 00z 06z 12z and 18z runs forecasting out to 84 hours.)

The RRFS, at least in last night’s situation, demonstrated a superior forecast to the existing older models.

No specific release date has been made for the RRFS and its ensemble version, the REFS, but early 2026 is a good bet.

The NWS has already solicited comments regarding planned discontinuation of several older models including the SREF and the HRESW models. Likely to be included in the discontinued list will be the NAM.

The RRFS and the REFS have clearly been developed to replace the functionality of the older models. I’ve been using the RRFS experimental version as my principal model over many months now and the RRFS appears to be, overall, an improvement in forecasting.

Showers early Monday morning?

Posted Sunday 08/24/25 @ 11:20 PM — An interesting setup for early Monday morning. The 00z NAM-NEST and 00z HRRR show a broken line of showers and possibly thunderstorms moving through about 5AM -6 AM. The experimental 00z RRFS shows almost nothing. It will be interesting to see what happens.

Sunday Update

Posted Saturday 08/23/25 @ 9:13 PM — Sunday looks to be dry. All models show the line of showers that moves to our west will fall apart. A few sprinkles are possible from this same system before daybreak Monday.

Also on Sunday, a weak system in the western Atlantic will bring some clouds to NJ, both in the morning and again the mid afternoon Sunday. The Philadelphia area will see a very thick layer of cirrus clouds, but dimmed sunshine should be able to pass through.

18z RRFS model forecast for 3 PM Sunday. Thick layer of high clouds (tan) around the city. Dimmed sunshine. More cloudiness at the shore (mid level clouds- maroon) at the shore. (Click on image for a larger view.)

The coming week looks dry. No systems expected to bring any rain. So we’re in another dry spell.

Posted Saturday 08/23/25 @ 9:58 AM —The latest model guidance shows it being a bit more windy today (Saturday) than previously forecast. Otherwise, beautiful.

Here’s the wind meteogram for Blue Bell, PA—

06z RRFS forecast wind speed/gusts for grid point Blue Bell, PA Saturday through Monday. Gusty winds towards evening from the south, then southeast. (Click on image for a larger view.)

Originally Posted Fri 9:56 PM —The beautiful weather will continue through early Sunday. High pressure maintains its hold through Saturday, but a southeasterly flow from a newly formed weak coastal low and a front to our northwest that loses its upper air support will bring a bit more humidity and some cloudiness for Sunday afternoon and evening. (The shore stays sunny, according to the RRFS.)

18z RRFS clouds/precip at 3 PM Sunday. Approaching front falls apart due to wide, diffuse and split jet streak aloft. (Click on image for a larger view.)

Showers originally expected for Sunday afternoon will likely fall apart as they approach Philadelphia due to a diffuse, broken jet streak.

Saturday Forecast

Sunny and quite nice. High 84° Blue Bell, 83°Philadelphia (not a typo)

Sunday Forecast

Somewhat increased humidity, but dew points still in the low 60s. High thin clouds in the morning lower to mid level clouds in the afternoon. No showers expected until later in the evening. Most areas may receive little or no rain; any rain will be light.

NBM high temperatures: Blue Bell, PA 84º Philadelphia, PA 83º
Uncertainty (based on standard deviation): ±1.4º