Monthly Archives: July 2025

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

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#Philadelphia #weather #PAwx #PhillyWx

Wednesday and Wild Weather Thursday

Posted Wednesday 07/30/25 @ 9:41 AM — With temperatures close to the highs reached on Tuesday, but with humidity (dew points) possibly higher, today (Wednesday) will be very hot again. Here’s the latest 12z Model Blend (NBM) just available—

NBM (Model Blend) forecast highs for Wednesday. (Click on image for a larger view.)

Apparent Temperatures (Heat Index) will be in the 101º-105º range, peaking about 2:30-3 PM.

As for Thursday, a cold front will approach. There are signs that severe weather will be a possibility. Timing is currently 2-7 PM. Thunderstorms will be most numerous about 4:30 PM-6 PM. This timing may change.

Specifically, the NBM hourly “tornado probability” parameter is registering in the 1.2% range for the immediate PHL area. That may not sound very high, but on previous days this entire season, its value hasn’t exceeded 0.1% in our region. So it’s 12x higher than previous days this season. Stay tuned.

Tuesday Forecast Review & Wednesday Outlook

Posted Tuesday 07/29/25 @ 5:18 PM — Well, the high at Philadelphia airport was 98º about 3:54 PM and the dew point was 70º. (The transient 99º will likely be ignored.)

What’s interesting is the RTMA, at 3:45 PM (runs every 15 minutes) shows the same temperature 97 as the official record, but lower dew points.

RTMA temps at 3:45 (Click on image for a larger view.)

RTMA dew points at 3:45 PM

RTMA dew points at 3:45 PM. Significantly lower than the actual recorded dew point. I’m not sure why they happens. Another model, the URMA will be available 6 hours later and may recalibrate the dew points to the actual observations. (Click on image for a larger view.)

Here’s the forecast highs for Wednesday (NBM)

18z NBM forecast high temps Wednesday. Dew points similar to today. (Click on image for a larger view.)
Tuesday Heat

Posted Tuesday 07/29/25 @ 9:32 AM — Today, we’ll likely see temperatures reach areas that are very hot, but I would still reserve the term “extreme” for actual temperatures in excess of 100º.

Today’s 12z NBM, just available, shows high temperatures in the upper 90s. (Click on image for a larger view.)

The latest NBM forecasts dew points that are likely (possibly) too high—

12z NBM dew points at 3 PM. Likely (possibly) too high again. (Click on image for a larger view.)

Today’s deterministic numerical models, particularly the NOAA models, keep the dew points in the 70s. However, the AI models have the dew points falling into the upper 60s after noontime, which will keep the over-hyped “Heat Index” or “Feels Like” temperatures lower.

The AI models were correct in yesterday’s dew point forecasts.

As I said yesterday, it’s not unusual to have dew point temperature forecasts be inaccurate, and that’s a reason why “Feels Like” temperature forecasts can sensationalize and be inaccurate since “apparent temperature” forecasts depends on the forecast accuracy of two parameters, humidity and temperature, not just one.

I won’t be posting the NBM “Apparent Temperatures”, aka “Heat Index”, since today’s forecast dew points are a bit on the high side.

Yesterday’s experimental Canadian GDPS with “AI Spectral Nudging” did particularly well in its temperature forecast. Here it is for today—

00z GDPS with “AI Spectral Nudging” high temps (Click on image for a larger view.)

Here’s the GDPS-AI dew point temp forecast for the same time, 3 PM—

00z GDPS with “AI Spectral Nudging” dew points at the same time, 3 PM (Click on image for a larger view.)
Monday

Posted Monday 07/28/25 @ 4:02 PM — I didn’t want to say this, but this “heat wave” seems just a bit over-hyped by the media. Today’s dew points were significantly lower than had been forecast resulting in heat indices that were lower as a result. It’s summer, it’s 93º.

If actual temperatures were approaching 100º, I could understand the use of “extreme” in the forecasts , but..

Here’s the official data from PHL airport—

Dew points dropped below the forecast 70º range in the early afternoon resulting in just a regular summer hot day.
(Click on image for a larger view.) Source: https://www.weather.gov/wrh/timeseries?site=kphl

That said, actual temperatures are expected to be higher on Tuesday and Wednesday. But it’s not unusual to have dew point temperature forecasts go wrong and that’s another reason why “Feels Like” temperature forecasts can sensationalize and be inaccurate to boot.

BTW, over past years, I’ve been asked which is my favorite weather app for mobile. Many of them are quite ok and I don’t use any particular one.

I really use my mobile web app (Safari) and and I really like this official web site for local conditions: NWS IDS Forecasts

For live radar, I like something that’s truly live. Many of the apps are delayed images. I’ve subscribed to WeatherTap for over 26 years. They’re not cheap, but I like their radar images on the go.

Adding to that, I use a this for current conditions in nearby official sites—
https://www.weather.gov/wrh/timeseries?site=kphl

https://www.weather.gov/wrh/timeseries?site=klom

I have four computers running 24 hours a day automatically downloading and processing weather models. I access these on mobile via a vpn. For excellent weather model data visualization, I use LuckGrib to display my own downloaded data. There is no better app than this for weather grib data visualization, available for iPhone, iPad or Mac.

Posted Monday 07/28/25 @ 9:10 AM — No news here. It’s going to be hot and humid. Here’s the model blend (NBM) forecast highs and heat indices—

06z NBM forecast high temps (± 1.6º) (Click on image for a larger view.)
06z NBM forecast heat indices (max) at 3 PM (Click on image for a larger view.)

Originally Posted Sun 8:40 PM —A very hot and humid flow of air returns for first half of this week. The upper level high pressure “heat dome” will be centered over the Southeastern US.

Water vapor imagery shows the upper circulation and the RAP model thickness over South Carolina is 582 dm which is quite high, indicating a very hot air mass. The clouds to our south are associated with the showers that moved through today—

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. Water Vapor Imagery reveals emitted water vapor infrared TEMPERATURE, NOT REFLECTED LIGHT from CLOUDS. (Click on image for a larger view.)

High temperatures over the next few days will be in the 90s with heat indices exceeding 100º here. Here’s the latest NBM forecast temps and dew points for Blue Bell—

Model Blend (NBM) Heat index (called “apparent temperature” in the models) Temperatures and dew points with standard deviations. (Click on image for a larger view.)

Thunderstorms likely Wednesday into Thursday.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Severity Update:

Posted Sunday 07/27/25 @ 12:14 PM — Greatest chance of severe weather today will likely be in southern Chester and Delaware Counties into S Jersey.

Sunday Update

Posted Sunday 07/27/25 @ 11:33 AM — In the short run, current radar and short range model guidance (RAP model) shows not much activity. Showers to our immediate west will enter an area of negative omega, diminishing strength of the storms—

Radar at 11 AM with RAP model low level Omega. Negative Omega will reduce intensity; Positive Omega to our south will increase activity, but that will stay to our south in the short run. (Click on image for a larger view.)

The latest REFS shows showers and thunderstorms pick up between 3 PM and 4 PM in near Philadelphia (and Yankee Stadium) —

Saturday Forecast Update

Posted Saturday 07/26/25 @ 8:26 AM — Last night’s models have trended towards an increased likelihood of showers and thunderstorms, as early as 3-4 PM in western sections but most likely after 6-7 PM closer to the city.

Originally Posted Fri 10:11 PM —A weak cold front moved through late Friday afternoon with showers and thunderstorms. The front will stall just to our south on Saturday, allowing somewhat drier air to filter in. The front returns as a warm front Saturday night into Sunday with widespread showers and thunderstorms. Heavy rain possible as a trough develops behind the warm front. Much of Sunday looks wet.

18z RGEM forecast for noon Sunday (Click on image for a larger view.)

Saturday Forecast

Somewhat less hot and drier air on tap for Saturday with dew points in the upper 60s. There will be a mix of sun and periods of clouds with an increase in clouds during the afternoon. A scattered thunderstorm is possible late afternoon and evening.

NBM high temperatures: Blue Bell, PA 88º Philadelphia, PA 89º
Low Uncertainty (based on standard deviation): ± 1.3º

Sunday Forecast

Showers and thunderstorms develop Saturday night after midnight with the warm front advancing towards us. The front passes over us about 5 AM Sunday morning and showers and storms will linger through much of Sunday as a disturbance moves along the front. We may see some brightening skies late afternoon, but additional showers are possible in the evening.

NBM high temperatures: Blue Bell, PA 84º Philadelphia, PA 86º
Very High Uncertainty (based on standard deviation): ± 3.6º

Models guiding this forecast: ECMWF, GFS, NBM, RRFS, RGEM

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