Sunday, July 5, 2026 5:25 pm - Philadelphia Weekend Weather & Storm Forecasts

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Friday Forecast Update

Posted Friday 07/10/26 @ 9:06 AM — First, let’s look at the total rainfall for Thursday—

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.)

A few thunderstorm triggers are visible in the pipeline this morning—

Water Vapor image at XX with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , GFS potential vorticity contours (violet fine contours) with MRMS Radar. Potential vorticity triggers are the fine violet contours. (Click on image for a larger view.)

For today, Friday, high temperatures will range from 88º (Blue Bell) to 90º (KPHL). It will very humid with dew points in the low 70s.

Sunshine through high cirrus clouds this morning. Increasingly cloudy (sunshine through thicker clouds) after 1 PM from northwest to southeast. A few isolated -widely scattered storms after 2 PM. Organized activity moves in after 4- 5 PM from the west; the heaviest activity will be sliding just south of Philadelphia, into Chester and Delaware counties, but other areas may see scattered activity. The total rainfall (RRFS) shows this pattern—

06z RRFS **total** rainfall ; **Heaviest is expected just south and west of the city. Scattered activity elsewhere**. (Click on image for a larger view.)

The NBM (model blend) thunderstorm coverage at 5 PM gives a similar view—

06z NBM thunderstorm coverage at 5 PM **1 (Isolated):** 10% – 20% spatial coverage **2 (Scattered):** 30% – 50% spatial coverage **3-4 (Numerous):** **BLUE- RED** 60% – 100% spatial coverage (Click on image for a larger view.)

Muggy Friday

Posted Thursday 07/09/26 @ 7:50 PM — The rain will be exiting our area later this evening. Some clearing is expected and by Friday morning we should see sunshine through thin high clouds. What will be apparent will be the heat and humidity. While temperatures will ‘only’ be in the mid to upper 80s, dew points in the 70s will make it feel much more uncomfortable.

Clouds thicken between 2 and 3 PM Friday afternoon as another area of showers and storms moves in between 3 and 5 PM. Initially, these showers will be very widely scattered and isolated. Areal coverage of these showers should increase in the early evening.

There is a lack of model agreement regarding these showers. The GFS shows them not making it into Philadelphia; the NAM-NEST doesn’t show much shower activity at all. The HRRR as well as the RGEM shows showers many places but not near Philadelphia or the immediate suburbs. The RRFS and HRDPS are the most emphatic with these pop-up showers/storms and it’s what I’m leaning towards.

19z NBM Hourly probability of any rainfall. (yellow-20%) is a good probability when dealing with hourly rainfall. I’m using probabilities because of the uncertainty in tomorrow’s forecast. (Click on image for a larger view.)

Thursday Update

Posted Thursday 07/09/26 @ 8:27 AM — A few light sprinkles moved through some areas earlier. Additional storms and triggers for storm formation are in the pipeline.

Water Vapor image at 8:30 AM with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , RAP potential vorticity contours (yellow fine contours with dashed emphasis) with MRMS Radar (Click on image for a larger view.)

“Tracking” these storms like a freight train is really meaningless; additional storms will dynamically form near and over our area, particularly areas north and areas south of us.

Zooming in, the vertical motions directly over us have turned negative (downward) inhibiting rainfall, but just 2 hours ago, it was strongly positive. Very dynamic.

Water Vapor image with RAP model Omega (vertical motion). The dashed fine yellow contours over Philadelphia now are downward motion, inhibiting rainfall. The solid yellow contours (now to our south) support rainfall. (Click on image for a larger view.)

The morning models have some showers/thundershower developing and moving through as early as 11-12 noon. Additional showers during the afternoon and evening hours. It won’t be raining in any one area continuously but most areas will receive some rain today. Last night’s models suggested heaviest rains to our north and to our south. That is less obvious with today’s (06z) model runs. More importantly, look at what I call a “parameter match” with the RRFS, REFS, HRRR, HRDPS and NAM-NEST shows poor matches with actual current 3 hour conditions in the RTMA. This means that the models have a poor handle on the specifics.

Thursday Forecast

Posted Wednesday 07/08/26 @ 7:59 PM — I wanted to review a few more models. The HRRR also has storms developing before noon, somewhat earlier than the RRFS—

18z HRRR forecast for Thursday at noon. (Radar and 1 hour precipitation) Note that the 760 thickness is nowhere to be seen (it’s further south), indicating a lack of model agreement. The exact placement of the rain is never literal. Reality usually differs from the model forecast. (Click on image for a larger view.)

The HRRR also shows (not illustrated here) a second widespread batch of storms about 3-5 PM over the immediate Philadelphia area and southward.

The heaviest activity is forecast from the city southward, but again, the model placement of the heaviest activity is almost never literal.

With the exception of lightning and heavy rain potential, I don’t see parameters indicating severe weather like tornadoes. But the NWS has public safety as its mission, so expect severe thunderstorm watches and warnings tomorrow.

Posted Wednesday 07/08/26 @ 6:11 PM — Over the past couple of days, I’ve used water vapor (WV) images (with RAP model overlay) to show the advance of very moist air and higher temperatures back into our area. Here’s the latest WV image showing the edge of the heat dome and high humidity advancing towards us. The 576 thickness contour shows the advance compared to yesterday—

The models are showing the possibility of scattered light showers to our west in the morning, but all are showing much more significant rain/thunderstorms moving in around 2 PM Thursday. The amount of water in the air that can fall as rain (referred to as “precipitable water” or PWAT) is in the 2.2″ to 2.4″ range Thursday afternoon. That is very high. That means that any showers and storms has the ability to produce heavy downpours and possible flooding.

RRFS forecast for 2 PM Thursday. Some heavy-hitters to our west moving in. Note the orange contour, the 576 line. (Click on image for a larger view.)

I’d like to look at additional models and I hope to post again this evening. Stay tuned.

Wednesday through Friday Outlook

Posted Tuesday 07/07/26 @ 8:04 PM — The low stratocumulus cloud layer was difficult to scour out today. We should see sun Wednesday.

Wednesday will be the nicest day of this week. Highs 82º-84º

Water Vapor image at 4 PM Tuesday with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , GFS potential vorticity contours (violet fine contours) with MRMS Radar and surface wind barbs, **Note the edge of the heat dome (576 thickness) Storms are expected to form and follow just north of this edge Thursday through Saturday.** (Click on image for a larger view.)

From Thursday through Saturday, things become unsettled with not much model agreement regarding the advance of very hot air now in the Southeastern US. Some models have the boundary of this warm air moving back and forth over us. Other models keep it south of us.

Either way, it looks like we’ll be in the position for numerous showers and thunderstorms Thursday, Friday and Saturday. Exact timing is unclear at this time, but the setup favors afternoon showers and storms but possible other times as well. Stay tuned.

Tuesday – Wednesday Outlook

Posted Tuesday 07/07/26 @ 12:08 PM — The latest RRFS, just available, keeps the low clouds in our area through at least 3 PM with some brightening in some areas.

Posted Tuesday 07/07/26 @ 8:43 AM —

Tue 8:43 AM —Forecast Review — Much of the city and westward didn’t see the flareup in the rains in the afternoon as predicted by the RRFS. Some impressive rainfall was received by some areas. Here’s the two day total rainfall for our area—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED over the past 48 hours . Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch) (Click on image for a larger view.)

For today, Tuesday, a few widely scattered showers in the morning, then clouds should thin enough by noon or 1 PM to allow some sunshine through clouds, especially from the city and westward.

For Wednesday, sunshine returns, but the edge of the tropical heat dome is pushing on our doorstep by Wednesday evening. The return of heat and humidity is not expected to be as extreme as this past heat wave.

06z RRFS showing the 576 thickness contour, often associated with the edge of the “heat dome” and high pressure ridge in summer. (Click on image for a larger view.)

Mon 9:37 AM —Forecast Review — The 11 PM forecast time of the RRFS was impressive; with the exception of the very heavy rainfall in some areas, there wasn’t much severe weather reported. (Berks county, Kent county DE and Huntingdon County, NJ had flooding and strong wind gusts reported.)

Overall the SWEAT index wasn’t all that useful. The relatively new CWASP from the NBM (not used) wasn’t all that impressively severe and may be a better indicator of severe weather in the future.

No tornadic activity (helicity was only moderate) and timing of the main system wasn’t at time of peak CAPE.)

Here’s the rainfall totals through 8 AM today—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of **ACTUAL RAINFALL RECEIVED through 8 AM**. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch) (Click on image for a larger view.)

Monday

Posted Monday 07/06/26 @ 9:48 AM —Rain continues to develop this morning due to a convergence of thermal level winds at mid levels—

Theta-E (thermal potential energy) convergence causing storms to pop this morning. (Click on image for a larger view.)

The RRFS shows clouds thinning for some bright areas during the early afternoon. Heating of the day will cause more thunderstorms about 4-6 PM

06z RRFS forecast for 5 PM today. Thunderstorms develop over Philadelphia as the heat dome boundary (760 thickness -orange) is right over us. (Click on image for a larger view.)

Severe Weather Likely Sunday Evening

Originally Posted Sun 5:25 PM — The periphery of the “heat dome” (as captured by the 5760 thickness line) will be slipping slowly south of our area tonight. Strong waves and impulses are moving along this periphery and will spawn thunderstorms, some likely to be severe Sunday evening into the night.

This morning’s GFS captures this with the energy of the first wave and the edge of the heat dome—

Today’s 12z GFS forecast for 6 PM this evening. The 760 thickness line (more properly called **5760** meter line of the 1000mb-500mb atmospheric thickness; runs right through Philadelphia. A clear wave develops along this border and this will move towards us, possibly just north of us. (Click on image for a larger view.)

Storms are already developing in Western and Central PA. From the model timing, it appears that the storms in Western PA will more directly affect Philadelphia between 8 PM and midnight, with the storms ahead moving somewhat north of the Delaware Valley.

RADAR Satellite and mid upper level wind streams at 4:15 PM (Click on image for a larger view.)

Of great interest and concern is the “Severe Weather Threat Index” or SWEAT. I put this calculation together with the help of AI last year and it’s part of my routine RRFS model download post-processing. I have never seen it this high over the past year.

18z RRFS calculated SWEAT index at 11 PM. Anything over 400 has a strong chance of tornadic activity, hail and strong winds and severe weather. (Click on image for a larger view.)

Also of interest and concern is the “echo height”, a standard parameter of several models. The RRFS shows 52,000 feet at 11 PM at a different location. Again, a number I have rarely seen before.

RRFS echo heights at 11 PM 45,000 is fairly standard for strong to severe storms. 52,000 feet is extreme. (Click on image for a larger view.)

Finally, the simulated radar and rain at 11 PM—

Below is my “severity index”. I’ve revised it from past years to now use the new RRFS —

Severity Parameter (HRRR)	Sept 1 , 2021 Tornado Outbreak (example of highly severe)	4-1-23 Tornadoes (Example of severe)	08-07-23 18z HRRR Bow Echo	07-08-25 18z HRRR & Impact	Today 07-05-26 RRFS & Impact	Notes
CAPE Joules/kg	3500-4200 ⚑⚑⚑⚑	2100 ⚑⚑	2600 ⚑⚑	2680 ⚑⚑	3200 ⚑⚑⚑⚑	7 PM
Helicity m^2/s^2	1350 ⚑⚑⚑⚑⚑	655 ⚑⚑	726 ⚑⚑	403 ⚐	526 ⚑⚑
Vertical Shear 1/sec	40-46 ⚑⚑⚑	40-45 ⚑⚑⚑	30 ⚑	20 ⚐ ⇩	38 ⚑⚑⚑
Precipitable Water	2.7″ ⚑⚑⚑⚑	0.83” ↓	2.1″ ⚑⚑	2.6″ ⚑⚑⚑⚑	2.3″-2.4″ ⚑⚑⚑⚑	Heavy rain potential
Lifted Index º K	minus 6º ⚑⚑	minus 9.3º ⚑⚑⚑	minus 9.9º ⚑⚑⚑⚑	Minus 8.3º ⚑⚑	Minus 8.7º ⚑⚑⚑
HRRR Hail inches	1.9 ⚑⚑⚑	1.4 ⚑	1.8 ⚑⚑	1.8 ⚑⚑	1.9 ⚑⚑⚑
Peak Wind Gusts mph	40-50 ⚑⚑⚑	40-50 ⚑⚑	65mph ⚑⚑⚑	51.6mph ⚑⚑⚑	47mph ⚑⚑⚑
Max Updraft Helicity m2/sec2					200 ⚑⚑⚑
SWEAT Index					450 ⚑⚑⚑⚑⚑

It appears that the boundary/front will be near us to spark showers thunderstorms Monday afternoon and evening.

Philadelphia Weekend Weather & Storm Forecasts

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