Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

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Friday Storms

Posted Friday 08/07/26 @ 8:57 AM — A disturbance in Ohio/northwest Pennsylvania this morning will push towards us, into the ridge of the Bermuda high and the heat dome.

Water Vapor image at 8:26 AM with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , GFS potential vorticity contours (violet fine contours) with MRMS Radar

Showers and thunderstorms will develop today, Friday, as early as 3-4 PM in western sections and closer to the city around 6 PM to 8 PM. This will be a slow moving system, so repeated rains may occur. There is some indication that the majority of the heavy rain and storms will shear off to our northwest, in Lehigh and Berks counties, but Philadelphia and the immediate surround counties will likely see some storms.

As we’ve seen in recent forecasts, exact placement of the heaviest storms is close to impossible to predict in advance with each model having a somewhat different placement. Here’s the 07z Model Blend forecast at 4 PM and 7 PM—

07z NBM (model blend) forecast at 4 and 7 PM. (Click on image for a larger view.)
Thursday Evening and Friday Forecast

Posted Thursday 08/06/26 @ 5:56 PM — Wednesday’s weather was very wild, with at least four rounds of heavy rain. Here’s the total rainfall for Wednesday and Tuesday—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

What was so interesting about Wednesday evening’s storms- they hadn’t been explicitly forecast by any model and reviewing clues to what triggered the storm came up empty.

The usual ‘forcing’ mechanisms for such storms- dynamic, frontogenic, theta-e forced frontogenesis, moisture convergence and vorticity advection- all were not particularly impressive.

The only thing was extremely high dew points, moderate lifted index (-4 to -5). high 700 mb humidity and moderate CAPE.

For this evening (Thursday evening), there is somewhat more triggers showing, but the models aren’t predicting much except just west of the city.

Radar at 5:45 PM with RAP model Omega and upper air winds. (Click on image for a larger view.)

Looking at the above radar, neither the HRRR nor the RRFS are showing this activity. (The latest Canadian RDPS does show these storms) I wish I could say that they won’t affect the Phillies game tonight, but after last night, I can’t confidently advance that forecast. It’s likely they will stay to the west of the city, but I wouldn’t be surprised if some crop up in the city.

Friday looks to be sunny, hot and humid again. More widespread storms are expected beginning around 4 PM and continuing into the evening.

Thursday Forecast Outlook

Posted Wednesday 08/05/26 @ 9:11 PM — We had at least 3 rounds of rain today, at times, quite heavy. Here’s the MRMS rainfall totals through 7 PM—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.

More rain is possible this evening.

The models are showing little in the way of rain for Thursday until the evening. (Then again, the forecast accuracy wasn’t too stellar for today.)

While I’m not a fan of the heat index, the big story will be the intense humidity with dew points near 77º! This brings a regular hot summer day with a high of 90º into a heat index of over 100º—

19z NBM heat index (apparent temp) at 3 PM Thursday. (Click on image for a larger view.)
Wednesday Update

Posted Wednesday 08/05/26 @ 9:14 AM — Neither last night’s 00z or 06z models correctly forecast the early rain that moved in this morning. Looking at the new 12z models, they appear to be somewhat better at capturing what’s happening on radar—

Current radar at 12:10 PM More showers poised to move in (Click on image for a larger view.)

Beyond the next batch of rain, expected about 2 PM, the models show widely scattered light showers for the balance of the day and evening.

Wednesday

Posted Tuesday 08/04/26 @ 8:40 PM — An upper low circulation near Georgia will rotate moisture and high dew points into our area over the next several days following the passage of a warm front.

Water Vapor image at 8:30 PM 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, (Click on image for a larger view.)

The question for Wednesday— when will showers and thunderstorms move in? The ECMWF-AI model has showers moving in early late morning or noontime. Other models have showers moving in about 2-4 PM.

The showers/thunderstorms will be scattered and become more numerous about 5-7 PM with the actual passage of the warm front. The possibility of severe storms is greatest in western Chester and Montgomery counties.

Tuesday-Wednesday

Posted Monday 08/03/26 @ 4:47 PM — Additional storms broke out around noon in Philadelphia and moved eastward during the afternoon.

Here’s the final impressive MSMS rain totals for the past 24+ hours—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

Tuesday promises to be the best day of the week. Mostly sunny skies as high pressure builds in and humidity drops early in the day, but begins to increase towards evening. Highs near 85-86º

The tropical boundary to our south advances back north on Wednesday as a warm front and showers and thunderstorms will be frequent on Wednesday with high humidity. This high humidity situation where the heat index is actually meaningful- the high temperature will only be about 84º-85º but the heat index will be near 91º Considerable rainfall is possible on Wednesday.

ECMWF 3 hour prior rainfall at 2 PM Wednesday. 576 thickness line denotes general position of heat dome. (Click on image for a larger view.)

Originally Posted Mon 9:43 AM — Most areas had significant rainfall last night and heavier activity broke out this morning from the city eastward into NJ. Here’s the MRMS based rainfall totals from last night through 7 AM. (Totals have been increasing with this this morning’s storms.)

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED through 7 AM. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

Heavy activity continues at this time into New Jersey—

Water Vapor image at 9:15 AM with superimposed RAP models Omega and wind streams 850mb to 500mb Area of Omega (blue contours) in Delaware favors additional storms. (Click on image for a larger view.)

Additional storms are expected to develop this afternoon (Monday) from the Delaware River east into NJ. From the city and westward, little additional rain is forecast for today. The latest RRFS forecasts sunshine for Philadelphia and westward by this afternoon.

Tuesday is expected to be nicer than previously forecast, with plenty of sunshine at times through thin cirrus clouds.

Rain is again expected on Wednesday as the front that went through on Monday returns as a warm front.

ECMWF-AI forecast for Wednesday at 2 PM. Tropical boundary (orange) returns northward as a warm front. Another cold front is visible moving through the Great Lakes. (Click on image for a larger view.)