Monthly Archives: June 2025

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Friday Forecast & Weekend Outlook

Posted Thursday 06/12/25 @ 5:49 PM — A cold front will slowly slip through tonight into Friday morning. Most models are keeping the rain to near zero in the immediate Philadelphia area on Friday.

The REFS captures this well—

Today’s 12z REFS total rainfall through Friday evening. The rain stays to our north and south. (Click on image for a larger view.

Scattered light rain with periods of just clouds for Saturday as waves of low pressure move along this stalled frontal boundary. Sunday just looks to be cloudy with little in the way of showers. The timing of these waves will likely change. Stay tuned.

Thursday and Weekend Outlook

Posted Thursday 06/12/25 @ 9:11 AM — High temperatures for today will be near 90º in much of the area. Dew points near 65º will make the heat index (apparent temperature) about 1º higher than shown below.

NBM high temperatures expected 3-4 PM Thursday. (Click on image for a larger view.)

A cold front will slowly sink south of our area on Friday and will then become stationary. Some showers are expected from Allentown and northward with this front early Friday morning. While it will be cloudy here in our immediate area, no showers are current forecast here on Friday. (That may change.)

Some thinning of the clouds later Friday afternoon with some sun possible.

Weekend: A cooler easterly wind flow will develop behind this cold front with plenty of clouds.

Waves of low pressure will form along this front during the weekend. Periods of showers are expected, but timing these showers will be difficult.

The GFS has been consistently maintaining relatively low rainfall around the immediately Philadelphia area with much of the showers to our far northwest and to our south over the weekend. Total rainfall for the weekend only about 0.30″ (NBM) and 0.05″ (GFS).

06z GFS total rainfall forecast through 8 AM Monday. (Click on image for a larger view.)

But, it’s really too early to identify timing and exact locations of the heavier showers with any degree of certainty.

I’ll update later today.

Tuesday
Tue 7:09 PM —Forecast Review —The experiment with the short wave prediction from the experimental RRFS didn’t wasn’t a success. As late as 2 PM, the RRFS hourly was still showing showers to develop over Philadelphia from a short wave.
Both the 17z and 18z RRFS was showing significant dynamics (upward vertical velocity) at 5 PM, although the 18z had backed off a bit. Nonetheless, the forecast for rain didn’t verify. (Click on image for a larger view.)

At about the same time, the radar showed something trying to get going, but ultimately the forecast was a bust.

Radar at 5 PM showing something trying to develop in Philadelphia, but nothing really happened.. (Click on image for a larger view.)

These sorts of meteorological ‘experiments’ I thoroughly enjoy, even when the outcome is a bust. There’s always another day’s weather.

I should acknowledge that the RRFS is known to over-play this sort of convective rain forecast. Indeed, it’s one of the things they’ve been tinkering with to get the RRFS model ready for prime time release. The model is still considered experimental.

If and when they do release the model as operational, it will be likely known as RRFS-a. RRFS-b is already being explored, probably with a changed core from the current FV3 to a MPAS core. See my RRFS page for more info.

Posted Tuesday 06/10/25 @ 12:23 PM — Last night’s REFS correctly predicted the heavy rain that sprung up this morning over Philadelphia and northern sections. Last night’s (00z) HRRR really missed this forecast. I’m finding the experimental REFS increasingly useful and skillful.

Sticking with the REFS and the RRFS, the last two runs continue to show a break in the rain, but another short wave is expected to move through between 3 and 5 PM this afternoon with another round of showers, possibly some low level thundershowers. Let’s see if this happens.

REFS forecast at 4:59 PM shows short wave at 700 mb. Shading is relative humidity at 700 mb. (Click on image for a larger view.)
Tonight and Tuesday

Posted Monday 06/09/25 @ 6:03 PM — It was reasonably dry around here after 11 AM.

For the Phillies game this evening, it appears that the scattered showers originally expected this evening likely won’t materialize.

The rain will wait until after midnight to move in.

Rain ends Tuesday morning, by 10-11 AM in the city. About 0.35-0.40 inches of rain expected later tonight into Tuesday morning.

While the rain is expected to end Tuesday morning, several models show a ‘short wave’ moving through Tuesday afternoon about 3-6 PM with showers and possibly some thunder. Wednesday looks good!

RRFS forecast for 4 PM. 500 mb height contours (blue) show the undulation due to the short wave moving through. (Click on image for a larger view.)
Monday Forecast Update

Posted Monday 06/09/25 @ 9:22 AM — The latest ECMWF continues with light scattered showers through the day.

However, the latest RRFS, REFS and Canadian HRDPS forecasts no rain after 11 AM through the afternoon and based on current radar, I’m leaning in that direction. So low clouds with some breaks possible mid to late afternoon in western suburbs. Some widely scattered showers are possible as early as 6 PM. Light to moderate rain moves in tonight.

Latest Radar (~9 AM) shows exiting showers. Just an area to watch is is moderately strong upward 300mb vertical motion area indicated by (?) (Click on image for a larger view.)

Originally Posted Sun 4:49 PM —Some of the uncertainty with this weekend’s forecasts will spill into Monday.

The showers that did move in this afternoon (forecast best by the European AI-Single model as well as the regular ECMWF, and disappointingly forecast by the HRRR, RRFS, REFS, GFS and NAM-NEST) will continue to develop this evening and into Monday morning.

Radar GIF 3 PM Sunday More rain than forecast by several models. (Click on image for a larger view.)

The models are suggesting that the showers/rain taper late morning Monday with most (but not all) areas dry Monday afternoon. Rain redevelops Monday evening and night.

Here’s the latest ECMWF forecast for Monday afternoon, which shows the next element to affect our weather– another upper level low with a flow of cooler air.

ECMWF forecast for Monday at 4 PM. Upper level low in Canada, a dip in the jet stream with cooler air and the beginnings of low pressure expected to develop over the Ohio Vallye moving towards us for Tuesday. Rain expected Tuesday, possibly moderate rain. (Click on image for a larger view.)

Moderate rain on Tuesday, then things improve. Unfortunately, there’s a hint that we’ll see rain part of next weekend.

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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