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Sunday Update
Posted Sunday 07/20/25 @ 10:25 AM — A review of the models further advances the overall forecast trend noted last night: any showers/storms will be very widely scattered. The NAM-NEST continues to show a few isolated pop-up storms this evening around 8 PM, yet the models show any time after noontime is fair game for an isolated pop-up storm.
It should be noted that the GDPS with “AI Spectral Nudging” model has a forecast similar to my own inclination that the wind shift earlier in the day may significantly limit storms near Philadelphia. We’ll see.
Models used for this forecast: GDPS-AI, NBM, RRFS , NAM-NEST
Sunday Forecast Update
Posted Saturday 07/19/25 @ 9:10 PM — A warm front finally moves north of our area around daybreak Sunday. Showers before daybreak move out for partly sunny skies for much of the day. Heat and humidity returns, with highs 89-90º in the city and 87-88º northwest. It will become windy later in the afternoon.
A cold front moves through late afternoon. Only some of the ingredients are coming together for storms. While there’s plenty of jet stream energy nearby, we won’t be in an area where the jet causes much upward vertical motion. Additionally, the winds shift to the west before the actual front moves through. Historically, that often means very widely scattered storms; many areas may not see much of anything due to the infusion of drier air.
Storms that do form will be few and far between but could be severe with heavy rain and will most likely occur north and west of the immediate area. The chance of storms continues through 10 PM.
The NAM-NEST shows a few heavy hitters about 8-9 PM—
Models used for this forecast: NBM, RRFS , NAM-NEST
Originally Posted Fri 5:50 PM —The stalled front just to our south that kept considerable cloudiness in our area on Friday, especially southern sections, will return as a slow moving warm front on Saturday through Saturday night.
Warm fronts are not distinct like cold fronts and this front’s position and movement were not forecast accurately by the models for Friday. We’ll see if the model guidance is better over the weekend.
Saturday Forecast
Low clouds with widely scattered showers in the morning hours. More widespread heavier thunderstorms likely about 2-5 PM in the afternoon, especially near Philadelphia.
NBM high temperatures: Blue Bell, PA 83º Philadelphia, PA 85º
Moderate – Above Average Uncertainty (based on standard deviation): ± 2.5º
Sunday Forecast
Cloudy early morning, with clearing by early afternoon, if not earlier. A cold front moves through about 3-4 PM with more showers and thunderstorms. Heavier activity currently predicted for NJ.
NBM high temperatures: Blue Bell, PA 90º Philadelphia, PA 92º
Average Uncertainty (based on standard deviation): ± 1.5º
Models used for this forecast: NBM, RRFS , REFS, ECMWF-AI, HRRR, NAM-NEST
