Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

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Sun 8:42 AM —Forecast Review — Yesterday’s thunderstorms came through 3-4 hours earlier than forecast by any of the morning models. Looking back, the hourly HRRR began shifting the arrival of the storms to the earlier 1:30 PM to 2 PM ‘correct’ time with its noontime model run. Not much of a warning. I’m disappointed with the performance of the RRFS model with yesterday’s forecast.
Sunday Update

Posted Sunday 08/09/26 @ 8:47 AM — No surprises expected with today’s forecast. Sunshine with no rain or thundershowers expected today.

06z Model Blend high temperatures for Sunday. (Click on image for a larger view.)
Saturday Forecast Update

Posted Saturday 08/08/26 @ 10:01 AM — There’s a chance of showers and thunderstorms today. The big question is when?

Originally, showers and storms were forecast around midnight tonight. Things have changed. but there is poor model agreement regarding timing and placement of any showers and storms.

The only intersection of slight agreement is the HRRR, GFS, ECMWF, ICON and NBM, which show an area of storms right over Philadelphia around 4-6 PM. The RRFS shows this same 5 PM timing for storms, but it has the storms far west of the Delaware Valley and the REFS and HRDPS show nothing.

The NBM (Model Blend), not surprisingly, is leaning towards the HRRR.

NBM Thunderstorm Coverage (density over and an area) and 1 hour probability. Ratings designate area coverage as 1 (Isolated: 10%–20%), 2 (Scattered: 30%–50%), and 3–4 (Numerous: 60%–100%) coverage. The above shows Numerous in the reddish areas The center area (yellow) is 15% to 20% probability of thunderstorms in one hour. Doesn’t sound that high, but hourly probabilities can be 15-18% and still be quite likely.

Originally Posted Fri 8:07 PM — High pressure builds in for Saturday. A weak front approaches late Saturday evening and the surface trough lingers into Sunday. The trough falls apart later Sunday.

Saturday

Mostly sunny. Some thin cirrus cloudiness at times. Still humid with dew points near 75. The weak front produces widely scattered showers and thunderstorms Saturday evening about 8 PM to after midnight. Highs (Model Blend): Blue Bell- 89 º Philadelphia 90º ±4.0º (High sd and uncertainty).

18z NBM high temperatures Saturday. Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)
Sunday

A period of clouds in the morning. Then mostly sunny. Dew points still high, just under 75º Highs (Model Blend): Blue Bell- 91 º Philadelphia 89º ±2.7º Average sd and uncertainty.