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Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Uncertainty

Posted Sunday 06/08/25 @ 8:07 AM — I’ve been talking about an uncertain/low confidence forecast for this weekend and today, Sunday, is driving home that point.

Last night, the forecast for rain today had already been pushed from morning into mid-afternoon. The 06z models continue to show clouds at 8 AM, despite it being sunny now.

Current radar this morning is deceptive—

Radar ~ 8 AM with RAP model winds and Omega superimposed. The rain near DC is moving in our direction, BUT the winds at 10,000 feet have this rain moving abruptly to our east and south, possibly affecting south Jersey. (Click on image for a larger view.)

The latest REFS forecast (which did well yesterday) captures the same radar scenario as above, with minimal rain in Philadelphia even at 7 PM tonight—

00z REFS forecast rain plus statistical spread (contours) at 7 PM tonight. (Click on image for a larger view.)

However, even the REFS (along with the HRRR) show cloudiness right now, not the sun which is clearly visible through high cirrus.

The latest European AI model just became available and it accurately shows the the high cirrus. It maintains a forecast of clouds by afternoon with some light rain by 3-6 PM here in Philadelphia. So this AI generated forecast is what I’m going with today.

Forecast Update

Posted Saturday 06/07/25 @ 9:49 PM — A quick update. It now appears that the rain will not make into our area until 2-3 PM Sunday. The rain will be quite light at the start. The heaviest rain late Sunday will be east of the I-95 corridor.

18z REFS forecast for 4 PM Sunday (Click on image for a larger view.)

Posted Saturday 06/07/25 @ 9:46 AM — The REFS was spot-on with its forecast for rain to move in around 8:30 AM Saturday. I’m going to continue with REFS model forecast for the balance of Saturday and Sunday.

Saturday— continued cloudy with intermittent showers and possibly thundershowers. Shower activity picks up after 3 PM—

06z REFS model forecast- rain and statistical spread (contours) at 3 PM Saturday. (Click on image for a larger view.)

Sunday— cloudy. The latest REFS shows rain moving in earlier than previously forecast, as early as 9- 11 AM

06z REFS forecast for Sunday at 10 AM. rain and statistical spread (contours) (Click on image for a larger view.)

Originally Posted Fri 5:40 PM —This weekend’s forecast has clarified somewhat. As mentioned in yesterday’s post, there’s been a great deal of model spread (uncertainty) with the weekend forecast in recent days and that I’d likely lean towards the model that did the best forecasting today’s weather. Today’s best forecast was from the experimental (and hopefully soon to be released) REFS ensemble model. (The HRRR, NAM-NEST and NBM kept areas near the city and eastward dry.)

The REFS’s forecast from yesterday morning for today at 4 PM is shown below along with a radar loop from today below –

REFS forecast from 12z (8 AM) Thursday morning for today, Friday at 4 PM. The REFS (and the RRFS) were the only models that clearly showed rain as far east as the city and parts of NJ. The other models, the NBM, NAM-NEST and the HRES kept the rain to our northwest.
Here’s a radar loop from around 3 PM Friday. A closer fit to the REFS forecast with showers in Philadelphia and NJ. While the REFS did well, it still didn’t capture the showers in Cape May County. (Click on image for a larger view.)

So staying with the REFS, here’s my current forecast for Saturday and Sunday, with help from the ECMWF-AI model and the NBM

Saturday Forecast

Cloudy with periods of rain and thundershowers throughout the day. Skies may brighten a bit towards evening as the rain ends.

NBM high temperatures: Blue Bell, PA 79º Philadelphia, PA 82º
Higher than normal uncertainty (based on standard deviation): ± 3º

Sunday Forecast

Some bright spots, possibly some sun through clouds early. Increasingly cloudy by afternoon. Rain and thunderstorms moves in between 3 and 5 PM from the southwest and continue into the evening.

NBM high temperatures: Blue Bell, PA 75º Philadelphia, PA 577º
Very high uncertainty (based on standard deviation): ± 3.5º

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

A Low Confidence Forecast for Friday

Posted Thursday 06/05/25 @ 5:37 PM — The forecast for Friday and the coming weekend remains “up in the air”. The general trend has been for much of the area from the city and eastward to remain rain-free for Friday with increasing chances of some scattered showers at times during the day Saturday.

I think a few weather maps capture the current trend—

18z Model Blend (NBM) has no rain in the city or at the shore on Friday. (Click on image for a larger view.)
18z HREF, an ensemble blend of the NAM HRRR and HIRESW-ARW is similar to the NBM forecast. (Click on image for a larger view.)
12z REFS (experimental), an ensemble blend of the RRFS and the HRRR shows showers more eastward. (Click on image for a larger view.)

The European AI model, the ECMWF-AI Single, is closer to the REFS forecast, bringing the chance of light showers into NJ—

12z ECMWF-AI total rain forecast through Friday. (The ECMWF-AI suggests more widespread rain, but its forecast appearance is the result of it being a low resolution model) (Click on image for a larger view.)

So, we’ll see which model does the best with this system and l’ll lean on it for the weekend forecast tomorrow.

Thursday into the Weekend

Posted Wednesday 06/04/25 @ 5:41 PM — The smoke at several levels of the atmosphere may reduce the high temperatures on Thursday (originally expected to be near or above 90º according to the AI model) by a few degrees. The models are clustering closer to 88º to 89º for Thursday’s highs with some 90º temps northeast of our immediate area.

The forecast for Friday and this weekend still remains uncertain.

Some models have the rain/thunderstorms staying to our far north and far south on Friday, but the latest HRRR bring some showers into Philadelphia from the south early Friday morning, possibly dissipating afterwards.

As for the weekend, the GFS and ECMWF models have moved in the direction of the European AI model, with rain now possible for Saturday AND Sunday. But there may be a few periods of no rain during the daytime hours.

Looking Ahead

Posted Tuesday 06/03/25 @ 8:25 AM — Looking ahead, there’s some summery weather coming this Thursday, with temperatures likely breaking 90º in some areas.

The latest ECMWF AI model (which gives 6 hour forecasts with 2 PM being the closest to the high temperature time period) shows 90º+ at 2 PM (high temperatures likely about 4-5 PM). Dew points near 63º

ECMWF-AI

ECMWF-AI model high temperature at 2 PM. If correct, the highs for the day (reached at 4-5 PM) will be higher. (Click on image for a larger view.)

The NBM model blend (a statistical ensemble model) is in the same ball park—

NBM high temps forecast for Thursday.(Click on image for a larger view.)

The weekend forecast has high uncertainty with showers/rain Saturday and clearing on Sunday. The weekend forecast hinges on the uncertain position of a stalled front and the uncertain formation and track of a coastal low that’s expected to form.

Tuesday Forecast Update

Posted Monday 06/02/25 @ 5:54 PM — A building high pressure ridge will bring increasingly warm and more humid weather to our area through Friday.

A front will move through late Friday or Saturday with some showers and thundershowers, although the heaviest activity will likely remain north of the immediate Philadelphia area.

Of interest will be a smoke plume from wildfires in Canada that will bring considerably hazy skies. At ground level, smoke increases will be only slight, but perhaps noticeable.

18z HRRR-Smoke model Vertically integrated smoke concentration at 8 PM. Smoke increases during the daytime hours. Red is moderately high, but well short of the levels from several years ago. Luckily, this smoke is aloft, not very much near ground level. (Click on image for a larger view.)

Previously Posted Sun @ 7:40 PM — —An upper air low that is north of our region is expected to move away by Tuesday.

Today it was responsible for more clouds [than had been forecast by many models] and for the cooler than average temperatures. The upper low is visible in the satellite water vapor image—

Water Vapor 7 PM Sunday -Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), Mean Sea Level Pressure isobars (black contours) potential vorticity (fine violet contours) with superimposed MRMS RADAR. (Click on image for a larger view.)

Also dimming the sun today was smoke from forest fires in Canada. The smoke plumes are rotating around the upper low—

21z HRRR smoke model. Our area was on the fringe of this plume. (Click on image for a larger view.)

By Wednesday, an upper air ridge will be taking shape over the eastern US, bringing much warmer temperatures on a southwesterly wind flow—

18z GFS forecast for Wednesday morning shows high pressure and and upper ridge in control of our weather. A southwesterly flow of increasingly warm air will bring much warmer temperatures and dry conditions. I suspect that the smoke plume may affect us more this week.

The latest ECMWF-AI model has the cold front (visible on the graphic above) dropping south and likely stalling over our region for late Friday into Saturday. Some showers move in late Friday.

So, a transition period to warmer temperatures and possibly a different pattern looks to be the outlook.

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Due to the highly unbalanced political environment on X, I’ve considerably cut back auto-posting there. To receive all of my forecast postings, I recommend following me on mastodon.social or bluesky.social

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Sunshine through… Smoke

Posted Sunday 06/01/25 @ 10:37 AM — Ordinarily, I find the the expression “sunshine through high cirrus clouds” to be a useful description of a day’s cloud cover when the predominant cloud type is cirrus. Many people might not notice that the sunshine is filtered by high clouds.

Today, the appropriate sky forecast description is sunshine through smoke. The smoke from wildfires in Canada has made its way to our area in a reduced way. Here’s the latest HRRR smoke model forecast for this afternoon showing plumes of smoke —

Today’s HRRR smoke model forecast for 6 PM. While the 100 x 10 minus 6 kg/m2 doesn’t approach the 480 level we saw a few years ago. the sky will not be the bright blue we’d expect to see with a clean air mass. (Click on image for a larger view.)
Saturday Weather Update

Updated Saturday 05/31/25 @ 9:48 AM — Latest RREF shows the scattered showers as early as 1 PM.

Posted Saturday 05/31/25 @ 9:30 AM — We had the heavy rain last night; rainfall amounts and severity here were not as great as had been forecast possible.

Total rainfall received—

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.)

Additional showers are expected with the passage of a cold front this afternoon. Currently, these showers are in northwestern PA—

RADAR at 9:15 AM with superimposed RAP model parameters. (Click on image for a larger view.)

Most models show two areas moving towards us, as shown above, with the heaviest rain to our north and more so to our south.

Here’s the current HREF forecast for this afternoon—

Forecast for 2 PM this afternoon. Scattered showers, nothing severe. (Click on image for a larger view.)

A dry day for Sunday with sun mixing with instability cloudiness.

The weather really warms up next week, with temperatures in the mid to upper 80s Tuesday through Thursday.

Heavy Rain Possible Tonight

Posted Friday 05/30/25 @ 6:11 PM — One more thing. Helicity and vertical shear values become highly elevated between 10 PM and 1 AM. The potential for severe thunderstorms and even a tornado is possible, most likely in western suburbs.

Posted Friday 05/30/25 @ 6:11 PM — I’m a little short on time for this forecast, so I’m simply going to focus on Friday night at this point.

Showers and thunderstorms are developing to our south and will move in as early as 8-9 PM and will quickly become widespread by 10-11 PM.

HREF 18z forecast simulated radar 9 PM and 11 PM (Click on image for a larger view.)

Flood Watches have been issued for parts of the area. Total rainfall by 8 AM Saturday—

18z HREF forecast accumulated rainfall by 8 AM Saturday. Note that the exact locations and amounts are often not correct, but suggest possibilities. (Click on image for a larger view.)

Following a break Saturday morning, more rain is expected Saturday afternoon. I’ll update tomorrow morning.