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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 —

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) —

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—

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.

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.

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Friday Forecast Update

Posted Friday 05/22/26 @ 9:50 AM — We’ve had some breaks in the clouds and bright spots this morning as most models predicted last night. The RRFS, HRRR and NAM-NEST continue to forecast some breaks of sun on either side of noon time today near the city and areas north. Areas south of the city in southern Chester and Delaware counties will have the most cloudiness today.

As for the rain, as much as I’d like to use the new RRFS, the NAM-NEST seems to have the best match with current conditions. That translates into dry conditions for most of the day, although it does have rain creeping into southern Chester County and Delaware County by 4 PM.

As for the Phillies game at 6:40 PM, the same NAM-NEST is the most pessimistic, with some rain moving into the city.

The latest HRRR, RRFS and Canadian HRDPS keep this rain to our south during the game with just light sprinkles at most. Based on current match, I’m leaning unfortunately towards the wetter NAM-NEST.

The weekend continues to look wet, as it has for much of this week. But the fine details will make a difference in how good or bad this weekend’s weather will be. My regular Weekend Weather forecast follows later this afternoon or early evening.

Friday & Weekend Outlook

Originally Posted Thu 6:37 PM —The general trend for Friday has been for it to be dry with significant cloudiness, but with some bright spots especially around noontime into early afternoon. Northern suburbs will likely see less cloudiness and even some sunshine on Friday.

Most of the afternoon models (18z) have this as their forecast. Of interest is the 18z RRFS (the RRFS, our newest model, is often surprisingly good at forecasting cloud cover.)

The RRFS model has much more cloudiness, extending even further north. It also maintains the chance of some very light showers in the mid afternoon. Definitely an outlier, but it shouldn’t be ignored.

For now, we’ll go with the other more optimistic models for now.

The Memorial Day Weekend looks to be disturbingly cold, wet and cloudy. A stream of moisture from the Gulf of Mexico along with a stalled frontal boundary that will focus the rainfall right over us.

Saturday and Saturday night look to be quite wet, with potentially heavy rain.

The rain looks to last into Sunday morning, then dark low clouds for the rest of Sunday.

Monday looks to be very cloudy with a chance of widely scattered light showers, especially in NJ.