Daily Archives: Monday, July 21, 2025 9:20 am

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Update

Posted Friday 07/25/25 @ 5:11 PM — Not surprising, the storms have developed and moved closer to the city than forecast earlier. RAP model omega supports strengthening—

RADAR with superimposed RAP model Omega (Click on image for a larger view.)
Thunderstorms Friday Evening

Posted Friday 07/25/25 @ 11:46 AM — The models continue to show a good chance of scattered thunderstorms late afternoon and especially this evening. As early as 4 PM, most likely 6 PM – Midnight.

While not exact, the latest models suggest that the heaviest activity will be north of Philadelphia (Bucks County) and into central NJ and the central NJ shore. As was the case last summer, a localized heat dome over Philadelphia may diminish activity in the actual city.

13z RRFS forecast for Friday evening( Click on image for a larger view.)

Regarding potential severity, let’s compare to other events—

Severity Parameter
(HRRR)
(RRFS)		Sept 1 , 2021
Tornado Outbreak
(example of highly severe)		Recent
4-1-23
Tornadoes
(Example of severe)
Recent 08-07-23
18z HRRR Bow Echo		07-25-25
Today’s
13z
RRFS
&
Impact
Notes
CAPE
Joules/kg		3500-4200
⚑⚑⚑⚑		2100
⚑⚑		 2600
⚑⚑		3200
⚑⚑⚑
Helicity
m^2/s^2		 1350
⚑⚑⚑⚑⚑		655
⚑⚑		726
⚑⚑		379
⚑		Jersey Shore
Vertical Shear
1/sec		40-46
⚑⚑⚑		40-45
⚑⚑⚑		30
⚑		21
⚑		Central NJ
Precipitable Water 2.7″
⚑⚑⚑⚑		0.83”
↓ 		2.1″
⚑⚑
2.9″
⚑⚑⚑⚑
Heavy rain potential
Lifted Index
º K		minus 6º
⚑⚑		minus 9.3º
⚑⚑⚑		minus 9.9º
⚑⚑⚑		Minus 8.2º
⚑⚑		Central NJ
HRRR Hail
inches		1.9
⚑⚑		1.4
⚑		1.8
⚑⚑
1.7
⚑
Bucks Co
Peak Wind Gusts
mph		 40-50
⚑⚑		40-50
⚑⚑		65mph
⚑⚑		60 mph
⚑⚑		North NJ area
Storm Motion Shear Vector
Alignment		Aligned – ~ 90º
⚑⚑		Almost aligned
⚑⚑		aligned
⚑⚑		Not aligned
⚐
250 mb
Jet Stream Wind
mph		63
⚑		135
⚑⚑		74
⚑		38
⚐ ↓
Severity Parameters Impact: ⚑ indicates favors Severity ⚐ indicates Possible Severity
↓ indicates works against Severity ⇩ Significant, but less impact
Scattered Showers/Thunderstorms Late Friday

Posted Thursday 07/24/25 @ 8:05 PM — After reviewing several of this afternoon’s models, it appears that scattered showers and thunderstorms appear likely for late Friday afternoon into the evening hours. Where it does rain, rainfall may be heavy. Some activity as early as 4 PM, but most activity between 7 PM and midnight.


Here’s the latest REFS forecast—

12z REFS total accumulated rainfall by midnight Friday. (Click on image for a larger view.)

Each model had a different take on which area the showers occurred. As always, the forecast location of the rainfall is never to be taken literally.

Models which guided this forecast: RRFS , REFS, GFS HRRR

Very Hot Friday

Posted Thursday 07/24/25 @ 5:41 PM — The models have been extremely consistent forecasting a high of 97º± 1.5º near the airport and Citizens Bank Park) with heat index (“apparent temperature”) near or above 110º.

The model blend (NBM) captures the forecast highs for Friday afternoon—

18z NBM high temperatures for Friday. (Click on image for a larger view.)
18z NBM forecast heat indices for Friday. Max about 3 PM. (Click on image for a larger view.)

There’s a chance of thunderstorms, mostly western areas Friday evening due to another stalling front. Unsettled weather for the weekend, depending upon the final position of the stalled front and its passage back northward as a warm front.

Posted Tuesday 07/22/25 @ 8:52 PM — I just wanted to mention that the high temperatures forecast by the NBM model for Thursday and Friday are likely too low.

The latest ECMWF-AI model shows highs several degrees greater. Here’s the ECMWF-AI forecast temperature at 2 PM Friday, which is about two or so hours before the highest temperatures will be reached. (The “free” version of the AI model only forecasts in increments of 6 hours, so 4 PM temps are not available. )

Friday’s temps at 2 PM, (likely even higher at 4 PM)—

18z ECMWF-AI temperature forecast Friday 2 PM Fine contours are 1º increments (Click on image for a larger view.)

Posted Tuesday 07/22/25 @ 6:07 PM — The real heat waits until Friday.

Wednesday and Thursday look very warm, but dew points will remain in the upper 60s. By Friday, temperatures move into the mid 90s with dew points in the 70s, making for an extremely hot day.

18z NBM high temperatures for THURSDAY. Contour lines are 1º increments (Click on image for a larger view.)
18z NBM high temperatures for FRIDAY. Contour lines are 1º increments (Click on image for a larger view.)

I’m sorry to say that the weekend looks a bit unsettled, with showers at times.

Originally Posted Mon 9:20 AM ——This week’s weather will be influenced by a welcome mass of cooler air from Canada (Gee, I hope they don’t start using this export in the trade war.) We’ll have this relief today through some of Thursday.

06z ECMWF-AI forecast for Tuesday at 2 PM. (Some moisture in the easterly flow may cause some showers at the shore.) (Click on image for a larger view.)

By late Thursday, the return southwesterly flow will bring back some of the heat and humidity.

00z GDPS with “AI Spectral Nudging” forecast for Thursday afternoon. The orange line is the 576 line of the 500-1000 thickness parameter. It is a convenient marker for the three dimensional “edge” of tropical air. (Click on image for a larger view.)

We’ll have to see if any warm front develops on Wednesday in advance of the return of tropical air.

Models used for this forecast: GDPS-AI, ECMWF-AI