Category Archives: Philadelphia Weather Outlook

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 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.

A note for those of you who are visiting this site from “X“.
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 Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Friday Update

Posted Friday 05/30/25 @ 9:53 AM — The clouds should break for sunshine from west to east about 11 AM to noon. Cloudiness develops again about 4-5 PM. Light rain moves in about 7-9 PM. Heavier rain and possibly severe thunderstorms move in about 9 -11 PM Friday evening, according to the latest HRRR.

Today’s 12z HRRR forecast simulated radar- 10 PM Friday evening. (Click on image for a larger view.)

(Problems with NOAA’s supercomputers have been an issue over the past 18 hours, hopefully resolved. This has prevented availability of the RRFS and REFS.)

Update Thu 5/29 10:44 PM — Tonight’s early models suggest that Friday will be relatively rain free. Minimal isolated showers. Heavy rain and potentially severe storms move in and develop in place over our area beginning 6-8 PM.

Active Unsettled Weather Friday Saturday

Posted Thursday 05/29/25 @ 5:27 PM — Several pieces are coming together for some active weather (heavy rain, thunderstorms) beginning later Thursday night through at least Saturday.

The jet stream is forecast to dive south into a sharp trough (somewhat unusual for late Spring). This feature along with a southern stream jet flow will provide energy to spawn low pressure, rain and thunderstorms. Add to this an increasingly moist air flow with some forecast helicity, wind shear and the ingredients are in place for potential severe weather and heavy rainfall.

Today’s 12z ECMWF jet stream flow shows strong jet streak diving south and interacting with south jet flow, spawning waves of low pressure. (Click on image for a larger view.)

Timing of these soon-to-be spawned low pressure waves will be less than exact. As mentioned, the first wave moves through Thursday night with showers and some thunderstorms, ending early Friday morning.

A break in the action looks likely Friday morning, but there’s the possibility of some scattered storms forming Friday afternoon. The heavy action now appears to occur Friday evening and night, where severe thunderstorms are possible, especially in NJ. Rain and thunderstorms continue into Saturday. We may get a break on Sunday.

I expect to hear a few severe thunderstorm announcements over the next two days. Stay tuned.

Clearing Thursday- Possible Severe Storms Friday Afternoon

Posted Thursday 05/29/25 @ 8:42 AM — Sky conditions are expected to improve over this afternoon. Cloudiness will become quite variable in many areas between 2 and 5 PM. Enjoy while you can.

More clouds and what looks like possible severe storms Friday afternoon into Friday evening.

RRFS forecast Precipitation rate and upward helicity at 5 PM Friday. Suggestive of severe storm potential. (Click on image for a larger view.)
Wednesday -Thursday Update

Posted Wednesday 05/28/25 @ 4:33 PM — I rarely use the popular TV weather phrase “I’m tracking this [on radar]” to describe the progression of weather.

“Tracking” suggests to me a very non-dynamic process with weather moving from point A to point B, like on a train track. Indeed, the hourly rain depiction on the iPhone weather widget is that level of weather ‘forecasting’. Weather forecasting is much more complex than this.

Case in point is the current radar, which shows the back edge of the rain moving towards us at 4 PM. So, why did they postpone the Phillies game for this evening?

The reason is rain is expected to redevelop over us and increase in intensity despite the back edge visible on radar at this time.

Composite RADAR with RAP model parameters superimposed at 4 PM. Yellow contours depict vertical velocity. (Click on image for a larger view.)

The above radar image above includes RAP model vertical velocity (yellow X) which is expected to move over us during the early evening hours. Heavier rain is expected to redevelop with this dynamic in place Wednesday evening. (I guess we’ll see if it happens.)

The rain is expected to depart by the early morning, but low clouds will linger for much of the day Thursday.

Another possibly heavy rain maker is forecast to begin mid afternoon Friday.

Wednesday’s Rain

Posted Tuesday 05/27/25 @ 6:10 PM — This afternoon’s models are predicting remarkably similar rainfall totals for Wednesday, with higher rainfall to our south (a trend that has been consistent as well.)

To mix it up a bit, here’s the HREF ensemble model rainfall totals through 8 AM Thursday—

Today’s 18z HREF model rainfall forecast through 8 AM Thursday. (Click on image for a larger view.)

With the exception of the Canadian RGEM, most models have rain starting around daybreak Wednesday. As for the Phillies game Wednesday evening, it looks like the rain doesn’t taper until late evening.

The rain ends early Thursday morning, but plenty of clouds are forecast for much of the day, possibly breaking to some sunshine or bright skies late Thursday afternoon.

Tuesday-Wednesday Forecast Update

Posted Monday 05/26/25 @ 7:29 PM —It appears that cloudiness will advance earlier into our area Tuesday than previously forecast. Considerable cloudiness is expected during the morning, with thickening and lowering cloudiness during the day.

Many models have some light sprinkles after midnight into early Wednesday morning with heavier rain developing by late morning and during the afternoon. An easterly wind will make it quite chilly on Wednesday.

Rain will continue Wednesday evening and taper off Thursday morning. Slow clearing with a chance of a shower through Thursday.

12z RRFS-A (pre-release version) total rainfall through Thursday/ (Click on image for a larger view.)

The GFS, Canadian, ECMWF and RRFS are forecasting close to 1+ inch of rain total around Philadelphia, less amounts to our north. The AI versions of the ECMWF and the GFS show lesser amounts, about 0.5-0.75 inches with the heaviest rain south of our area.

Memorial Day through Wednesday

Originally Posted Sun 7:53 PM —Low pressure that slowly departed our area will still influence our weather on Monday, Memorial Day. We’ll see plenty of sunshine Monday, but several models are hinting at some cloudiness developing mid-afternoon into the evening as a short wave associated with the departing low rotates through.

The GFS and pre-release RRFS model show the possibility of a few isolated showers between 3 PM and 8 PM. Most areas will be dry. (The Canadian HRDPS keeps these showers far north of our area.)
(Updated Sunday 05/25/25 @ 9:12 PM —Several more of this afternoon’s models keep any isolated showers to our far north.)

12z RRFS-A (pre-release) model forecast for 8 PM Monday. (Click on image for a larger view.)

Tuesday will have sunshine through high cirrus clouds ahead of an approaching low pressure system. (Areas south of the city and in South Jersey may have considerable mid-level cloudiness.)

Also expected Tuesday is an updated NBM model, which will be moving to NBM version 4.3. This updated model will have several enhancements, including an update to cloud cover and improvements in forecasting tropical systems and severe weather.

Here’s the storm taking shape in the Central US as of Sunday evening —

Sunday evening 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. Storm taking shape in south central US. (Click on image for a larger view.)

This storm will bring rain to our area Wednesday. The trend has been for the heaviest rain to move to the south of our immediate area. About 0.5 inches of rain are expected.

Latest GFS forecast for Wednesday (Click on image for a larger view.)