Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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Friday Update

Posted Friday 01/09/26 @ 10:06 AM — Just as there was a dramatic change in the with Saturday’s high temperature forecast, a comparison of this morning’s models with the real time RTMA data suggests that the models are having some issues modeling today’s rain moving in.

Current (10AM) radar and Clear Channel (14) satellite image. The radar echos are closer than forecast by several models. (Click on image for a larger view.)

The actual observations (the RTMA) suggests that high pressure is blocking advance of the rain, while the advanced location of the line of showers west of our area suggests something quite different. The only thing I can say— there’s uncertainty with the amount of rain and its onset this afternoon.

It should be noted that the latest ECMWF is forecasting more rainfall this afternoon than was being forecast yesterday. Still going with 3-5 PM onset This continues to be an interesting system. Stay tuned.

Models guiding this forecast: HRRR, RTMA RRFS ECMWF

One More Thing

Posted Thursday 01/08/26 @ 7:54 PM — For days now, I (and everyone else) has been talking about temperatures reaching and exceeding 60º on Saturday. The forecast has changed significantly over the past 18-24 hours and the NBM (which is my go-to model for temperatures) has been slow to capture the trend.

The latest models from this afternoon (18z) are forecasting highs only in the mid 40s for Saturday due to an easterly flow instead of a previously forecast warmer southerly flow. The actual high temperatures will occur before noon on Saturday, dropping during the afternoon.

18z RRFS temperatures at 2 PM Fine black lines are 1º increments (Click on image for a larger view.)

Models guiding this forecast: GFS, NBM, RRFS , REFS, ECMWF-AI,

Rain moves in Late Afternoon Friday

Posted Thursday 01/08/26 @ 5:38 PM — The models have trended towards minimal/no rain before 4 PM for Philadelphia and its immediate western suburbs on Friday, somewhat earlier far western sections. Much of the day will cloudy, but a few bright intervals during the day. The Model Blend (NBM) is showing very light rain after 4 PM with totals less than 0.04″ but greater in western sections. Here’s the REFS forecast accumulation—

12z REFS forecast accumulated rainfall by10PM (Click on image for a larger view.)

Considerable rain for Saturday for most of the day. Clearing and sunny skies for Sunday.

Thursday through Sunday Outlook

Posted Wednesday 01/07/26 @ 11:30 AM — The forecast for above average temperatures through Saturday has been well-advertised. Here’s the NBM high temperature meteogram for Philadelphia—

12z NBM forecast Temperatures/Dew Points for grid point Philadelphia Center City. (Click on image for a larger view.)

Also as forecast, rain will move in on Friday, either early afternoon or mid to late afternoon.

There are differences between the models regarding the speed and development of this Friday system: The European and Canadian models are faster with rain moving in on Friday afternoon and much faster to move it out on Sunday.

The comparison below of the AIGFS and the ECMW-AI forecasts at 1 PM Sunday show significant differences:

Comparison of the rain coverage forecast for the six hours preceding 1 PM Sunday. AIGFS (slower) ECMWF-AI (faster). The Canadian GDPS-AI is somewhere in the middle of the two above.

If the AIGFS (and Canadian GDPS-AI) is correct, the Eagles will have to contend with some rain on Sunday. If the ECMWF-AI is correct, it will be mostly dry during the game.

Tuesday Update

Posted Tuesday 01/06/26 @ 9:34 AM —A low pressure system passing to our north this evening will bring a warm front through today followed by a cold front tomorrow. Despite the clouds this morning, it looks like sunshine through high clouds this afternoon.

Wednesday looks to be mostly sunny and quite windy. High 51º-52º

Thursday highs will be in the same 50-52º range during the daytime, but temperatures warm up further later Thursday evening.

There’s a range of model forecasts for the rain expected Friday through Saturday. The GFS and the AIGFS is slower with the rain onset on Friday and slower for it to exit on Sunday. There’s also a question of weather the rain will be substantial or less than 1/2″ total.

Todays’s 06z GFS forecast for 3 PM Friday. Rain doesn’t move in to the city until mid to late afternoon. (Click on image for a larger view.)

Models guiding this forecast: REFS, NBM, GFS. AIGFS

Originally Posted Sun 8:37 PM —This week’s main ‘theme’ will be an increase in warmth, expected to begin in earnest on Wednesday.

18z NBM (model blend) meteogram for temperature/dew point for KLOM Blue Bell. High temperatures on a gradual but consistent climb to near 50º on Wednesday.(Click on image for a larger view.)

Several systems are expected to pass to our north with any precipitation also staying north, extending as far south as Berks county on Monday.

For the Philadelphia region and the Delaware Valley, considerable cloudiness is expected on Monday as the low passes to our north and warm moist air is brought in aloft. Highs remain in the 30s.

Another system passes to our north on Wednesday, that brings a weak cold front through. The chill down from this front will be short-lived.

A slowly moving cold front approaching from the west with waves of low pressure moving along it will pass to our northwest on Friday; most of the precipitation (rain) will pass to our northwest. Yet another wave of low pressure moves up the same path on Saturday.

18z ECMWF-AI forecast for Friday early afternoon. The area of rain moves to our northwest, just brushing our area. (Click on image for a larger view.)

While the general features of this weather outlook are consistent across models, it would not take much of change in intensity or track to greatly change our area’s forecast and weather. Stay tuned.