Daily Archives: Friday, May 22, 2026 5:35 pm

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Monday Forecast Update

Posted Sunday 05/24/26 @ 4:39 PM — A cold front, currently in western Ohio, will move through during the day Monday. Here’s the current radar with a line of storms associated with the cold front in Ohio —

Current radar at 4:30 PM Sunday with RAP model 700 mb relative humidity (coloration) Storm motion (yellow arrow) is northeastward as the line moves to the east. (Click on image for a larger view.)

We’ll wake up to scattered showers on Monday as the front moves towards us. The front is expected to move through Philadelphia about 11 AM to 3 PM with possible rumbles of thunder more likely in southern areas near Delaware and Maryland. Some clearing possible after the front moves through. Total additional rainfall is below 0.20″ in most areas except Southern NJ where some higher amounts may occur.

Some low level thunderstorm activity is possibly in S. Jersey and at the shore late afternoon into the early evening.

Forecast Update

Posted Sunday 05/24/26 @ 9:51 AM — The rain is gradually moving away by later this morning, but low clouds and possibly some mist is forecast for the rest of the day. Another disturbance will move through from the west Monday morning with lighter showers for much of Monday, but some brightness and sunshine may emerge from southwest to northeast mid to late Monday afternoon. The shore will be the last to see this sunshine around sunset.

Sun 9:58 AM —Forecast Review —Yesterday’s expressed hedge regarding the high rain totals for this weekend proved to be unfounded. We’ve had the heavy rain in many areas as forecast by Friday’s the ECMWF, GFS, ICON and Canadian AI-modified models. The NBM which I reflexively use, under-forecast the rainfall as did some of the AI models. (I would have liked to see the performance of the new RRFS, but it was unavailable for 24 hours.)

Here’s the latest MRMS rainfall totals at 8 AM. This graphic is a ‘second pass’ calibration, so it probably captures only the rainfall through 5 AM. Later runs will capture a more complete accounting, especially of the this morning’s heavy rainfall.

Here’s what the ECMWF predicted on Friday through 5 PM Sunday (not an exact time match) —

Friday’s 06z ECMWF total rainfall through Sunday at 5 PM. Not an exact time match but pretty good as precipitation forecasts go. (Click on image for a larger view.)

I should probably indicate somewhere on this site that none of the writing, forecasts, or commentary on this site are written by AI or assisted by AI.

Over recent months, I’ve begun to use AI for help developing algorithms that perform complex parameter calculations of the downloaded raw model data. I use both Anthropic’s Claude and OpenAI’s ChatGPT. It’s absolutely fascinating!

You’ll be seeing the fruits of these efforts in coming weeks, and they are being incorporated into my existing automated model downloads post-processing scripts.

You’ll be seeing some new model graphics- “Q vector analysis”, frontogenic forcing, dynamic forcing, Theta-E frontogenics and lapse rates. Very useful for thunderstorm prediction and heavy rain/snow banding. Hopefully it will improve my forecasts.

Posted Saturday 05/23/26 @ 10:03 AM — This weekend’s weather forecast for extremely heavy rain had been consistent for days, but over the past 12 hours, the forecast appears to have greater uncertainty.

The most significant change has been the shift of the convergence zone for the heaviest rain to our north, instead of remaining right over us—

05-23-26 current radar/water vapor with RAP model Isentropic omega overlay. Main area of convergence to our north. Still triggers for more showers to our south. (Click on image for a larger view.)

What does this all mean? Difficult to say since all the models today are a poor match for current conditions.

Right now, it appears that our rainfall totals will be less than previously forecast and the rain activity will become more showery. I’ll be updating this afternoon if I see a trend. It also suggests that things might improve for Sunday and Monday, although the latest ECMWF-AI model still shows plenty of inclement weather for the weekend. (What’s become my favorite model, the soon to be operational RRFS, has not been available over the past 24 hours.)

Originally Posted Fri 5:35 PM —The rain moved in close to today’s NAM-NEST forecast and it will continue through tonight, Saturday and Saturday night into Sunday morning. The moisture feed supplying this rain event is direct from the Gulf of Mexico America Mexico. The moisture will over-run a stalled

frontal boundary and collide with colder high pressure to the north.

Rainfall amounts are expected to be in the 2+ inch range for much of the area, according the the Model Blend.

19z NBM total rainfall through Monday night. (Click on image for a larger view.)
Saturday

Rain, heavy at times. Windy and chilly. Highs: Blue Bell- 56º Philadelphia 58º ± 2.0º Average sd and uncertainty.

Sunday

Rain in the morning, then becoming more intermittent. Cloudy Blue Bell- 68 º Philadelphia 70º ± 4.7 º Above average sd and higher than usual uncertainty.

Monday

Cloudy with a chance of scattered showers. (Model Blend): Blue Bell- 77º Philadelphia 78º ± 4.6º High sd and high uncertainty.

Monday’s forecast is ‘up in the air’. I suspect it will change.