Daily Archives: Sunday, October 5, 2025 5:10 pm

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Forecast Evolves with Uncertainty

Posted Friday 10/10/25 @ 8:51 AM —A coastal storm will form over the next 24 hours due to a dip in the jet flow. Here’s the current water vapor image with RAP model overlay—

ECMWF-AI forecast 300 mb heights and wind speed (jet stream level). Coastal surface low forms. (Click on image for a larger view.)

Interaction with two upper closed lows, blocking high pressure to the north and Tropical Storm Jerry gives uncertainty in the track of the storm—

ECMWF-Ensemble (statistical) forecast shows elongated pressure area uncertainty with two possible tracks (double arrows) (Click on image for a larger view.)

The latest models suggest less intensity, less tropical characteristics and increased uncertainty regarding track close to our area compared to yesterday’s models. Instead of one center, the storm may evolve into two centers.

Slow movement due to blocking high pressure to the north and interaction with the upper lows will cause the storm to affect our weather from late Saturday through Monday.

The upper low near the Great Lakes will cause some showers to break out ahead of the coastal storm, as early as Saturday.

The latest REFS shows extremely scattered light showers and drizzle possible as early as Saturday morning—

REFS Multi-hour total accumulated rain by 2 PM Saturday. Rainfall will be very light and scattered on Saturday. (Click on image for a larger view.)

I’ll post my regular Weekend Weather Forecast later this afternoon, likely by 6 PM. Stay tuned

Coastal Storm Uncertainty

Posted Thursday 10/09/25 @ 7:50 PM — There seemed to be more model agreement yesterday than today regarding the coastal storm evolution and track. As mentioned, this is a complex system involving interaction between an upper low, a developing surface low along the coast, and a blocking high pressure system.

The latest GFS model has a track closest to the coast. This is supported by the German ICON model and the GFS-AI. The ECMWF, ECMWF Ensemble and the Canadian AI show a storm track more off-shore but with the storm taking a westward jog towards the Jersey coast. The latest ECMWF-AI has less of a westward jog and is somewhat more offshore, in line with the Canadian RGEM. Here’s the latest NAEFS forecast for Sunday afternoon—

12z NAEFS forecast for 5 PM Sunday. (Click on image for larger view.)

There’s too much uncertainty right now with timing the start of the rain (possibly as early as Saturday afternoon) and areas of heavy rain (NBM has many areas receiving 1.5-3″ of rain.). High wind gusts will also be an issue at the Jersey Shore. Stay tuned.

Interesting Late Weekend Storm

Posted Wednesday 10/08/25 @ 7:39 PM — Subsequent to my posting about 2 hours ago, the latest GFS model forecast became available. It shows moisture streaming up from the expected coastal system on Saturday to bring considerable cloudiness. The GFS is faster with the approach of the system and shows rain here by daybreak Sunday.

The GFS also suggests a strong tropical storm nature to the system with a very warm core. What’s so strange is the forecast precipitation pattern, suggesting at least at this early point, that Philadelphia may again lie in the precipitation doughnut hole of low precipitation. Hopefully this will change.

GFS forecast for 8 AM Sunday. The storm is just beginning to take shape. The orange contour (760 thickness line) around the center suggests a tropical warm center to this storm. (Click on image for a larger view.)
Thursday Forecast & Interesting Late Weekend Storm

Posted Wednesday 10/08/25 @ 5:40 PM —As we can see from the MRMS summary graphic below, most areas in the immediate Philadelphia area received very little rainfall last night and this morning. High pressure builds in through early Saturday, giving us mostly sunny skies, cool temperatures and more dry weather.

An interesting low pressure development is forecast to form off the coast of South Carolina. Some models give this semi-tropical characteristics and most models have the angular momentum of this system trying to merge with a closed upper level low developing near the Great Lakes. With two centers of circulation, this will be a difficult system to accurately model. Most models have this surface system retrograding towards the NJ shore late Sunday into Monday with heavy rain possible at the Jersey Shore and also near Philadelphia. The GFS-AI, like the ECMWF-AI model have the storm forming closer to the coast and then hugging the coast. Other models show more tropical characteristics, forming further off-shore but then retrograding towards the coast.

GFS Graphcast-AI model forecast for Sunday at 2 PM. It should be noted that there are several scenarios with some models having the rain move in earlier on Sunday. (Click on image for a larger view.)

After over two weeks of beautiful but meteorologically boring weather, this promises to be interesting. Stay tuned.

Wed 5:37 PM —Forecast Review — Actual rainfall last night and this morning, according the the MRMS model.
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.)

Wed 9:46 AM —Forecast Review — The models did fairly good with the timing of the rain, but the actual quantity of rain that fell in our area appears to have been significantly less than forecast and the location of the heaviest bands of rain to be just east of the I-95 corridor was not accurate. (This is often the case, but with rainfall, model errors are much less obvious than when it’s snowfall.) It’s too soon to post the MRMS rainfall totals, but I’ll do that later today.

We still need much more rain and our next possibility is a coastal system that moves up towards us later Sunday.

Rain ends here in the city between 10- 11 AM and clearing should occur rapidly by 12-1 PM. It should be noted that some models have some low clouds redeveloping from the city and westward during the early afternoon, so rapid clearing won’t occur in all areas.

Tuesday thru Wednesday

Posted Tuesday 10/07/25 @ 4:42 PM — The models continue with a trend for the immediate Philadelphia area and its western suburbs to miss out on the heavy (much-needed) rain tonight. The latest REFS forecast (supported by the latest ECMWF-AI model) is for the heaviest rain to fall east of the I-95 corridor. Here’s the total rainfall predicted by the REFS—

REFS model rainfall forecast. The REFS is a statistical ensemble model and the above is the “probability matched-mean” accumulated rainfall forecast (Click on image for a larger view.)

Some cells of heavy rain and thunderstorms are possible before daybreak Wednesday in South Jersey.

Rain ends from west to east Wednesday morning, likely over by 9 AM in the city and later in NJ. Clouds break for some sun by the afternoon.

We Need the Rain

Posted Tuesday 10/07/25 @ 7:39 AM — It’s been very dry over several weeks (actually low rainfall over several months). A cold front will move through, now after midnight, into Wednesday morning. Showers and possible thunderstorms will accompany the front.

Over past days, the models have clustered on about 0.5″ to 0.75″ of rain. Some of last night’s models, especially the RRFS, have shifted towards the heavier rain missing the immediate Philadelphia area with only light accumulations here. We’ll have to see, but it wouldn’t surprise me if the RRFS is correct.

Last night’s 00z RRFS total rainfall by Wednesday afternoon. (Click on image for a larger view.)
Forecast Update
Mon 9:54 AM —Forecast Review — Many areas had dense fog early this morning, but some areas did not. The RRFS and REFS did better than the NAM-NEST and NBM in forecasting the fog coverage.

Today’s (Monday) forecast looks on track.

Here are the changes in the forecast: Tuesday looks to be mostly sunny and warm with highs 79-81º. It will also become windy.

Many models have shifted the rain from late Tuesday evening into after midnight and Wednesday morning. Rain will end from west to east between noon and 1 PM. Clouds will likely linger into mid afternoon Wednesday.

06z RRFS simulated radar on Wednesday at 8 AM. (Click on image for a larger view.)

Colder and windy on Thursday.

Originally Posted Sun 5:10 PM —The picture perfect weather we’ve been having should last through early Tuesday, with a few modifications. Monday morning is likely to start out quite foggy, but the fog will lift by mid to late morning with sunshine for the balance of the day.

Temperatures on Monday will be in the low 80s with dew points remaining in the still reasonably comfortable low 60s.

Clouds move in Tuesday afternoon as a cold front approaches from the northwest. Clouds are not expected before 3-5 PM. Rain and possibly some thunderstorms expected Tuesday night through Wednesday morning.

NAEFS forecast for Tuesday evening 11 PM. Cold front and associated rain. (Click on image for a larger view.)

Total predicted rainfall varies with as little as 0.3″ (Canadian RGEM) and the RRFS to about 0.75-1″ (NBM, GFS, ECMWF-AI). We need the rain and the amount forecast and the current pattern doesn’t bode well in the rain department.

18z NBM forecast total rainfall late Tuesday trough Wednesday. As always, forecast placement of the actual heavier rain is rarely exact, but it gives a sense of the range of the rainfall expected. (Click on image for a larger view.)

Cold high pressure moves in for late Wednesday into Thursday with sunshine and likely some wind. It will likely be quite autumnal by later Thursday.