Monthly Archives: June 2026

Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

4 Comments

#Philadelphia #weather #PAwx #PhillyWx

Friday & the Weekend Outlook

Posted Friday 07/03/26 @ 7:26 PM — We hit an official high of 102º, this time captured by the RTMA at 4 PM

RTMA 20z High Temperatures. Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)

Right now, it appears that both the 12z and 18z runs of the RRFS have over-forecast thunderstorms again. That said, a line of storms has developed to our north, moving towards northern parts of our area. The caption explains why these storms may fall apart or weaken as they approach—

7 PM Radar and RAP model 700 mb wind streams. The dashed yellow line is where the RAP model is showing the Omega (vertical motion) turning downward which may cause the storms to weaken or dissipate as they approach. (Click on image for a larger view.)
Friday Update

Posted Friday 07/03/26 @ 10:21 AM — First I want to address the discrepancy between my reported high of 102º yesterday and the actual official 103º high for Thursday. I emailed the NOAA Mount Holly office inquiring about the RTMA and the online 5 minute data showing 102º and the reported 103º official high discrepancy. Here’s their reply—

“The hourly and 5 minute observations are reported in whole degrees Celsius; the website which displays it then converts the observation to Fahrenheit. However, the temperature sensor measures in Fahrenheit. Consequently, there can be rounding errors in the multiple conversion processes with the observations.  The preliminary daily climate summary is based on the sensor data, not a maximum or minimum of the observations.”

This seems more than a bit overly convoluted and I’m not sure I really understand why any errors resulting from multiple ºF<—>ºC convertion rounding wouldn’t be compensated for on their websites. But that’s the official story.

The official high temperature is posted online here daily about 5:30 PM.

For today, Friday, the NBM, which has done so well past days, is forecasting these high temperatures—

This morning’s 12z max Temp (Model Blend- NBM) for Friday. Highs are reached usually between 3:30 PM and 5 PM. (Click on image for a larger view.)

As for rainfall today and this evening, the ECMWF-AI model keeps any showers far north away from our area, as does the latest HRRR. The RRFS, which in its current first release version, has a known bias to over-forecast convective precipitation, is predicting widely scattered showers here at about 8 PM- midnight. We may be learning that our newest model has some issues. Then again, the Canadian HRDPS is also forecasting showers. I guess we’ll see.

Friday Forecast

Posted Thursday 07/02/26 @ 7:57 PM — For Friday, I’m sticking with the Model Blend (NBM model) which has performed the best over the past three days. (The ECMWF has been forecasting max temps that are too high. The new RRFS model has been very disappointing regarding its temperature forecasts which are too low by as much as 2º-4º!)

The high temperatures being forecast for Friday are expected to be about 1º higher than Thursday—

Today’s 18z Model Blend (NBM) high temperature forecast for Friday. Likely to occur about 4-5 PM. (Click on image for a larger view.)

As for the chance of rain, the RRFS shows a cluster of thunderstorms moving through between 7 PM and 9 PM Friday evening. Not all areas will receive rain. I’ll need to look at the water vapor image Friday morning to have greater confidence in this rain forecast.

Thu 7:45 PM —Forecast Review —Here are the RTMA high temperatures at 4:45 PM Thursday.
RTMA Temperatures recorded at 4:45 PM Thursday. The RTMA temps are confirmed 6 hours later by the URMA model, not yet available. (Click on image for a larger view.)

Thursday Forecast Update

Posted Thursday 07/02/26 @ 10:18 AM — Today’s forecast high temperatures remain unchanged from yesterday. Actual Temps, not Heat Index.

This morning’s 12z NBM 12 hour Temp Max Actual Temperatures Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)

Yesterday’s ECMWF and NBM forecasts were spot-on. Here’s today’s ECMWF Thursday’s high temperature forecast—

This morning’s (06z) ECMWF forecast high temperatures (5 PM) for Thursday. Fine Contours are near-surface (2m) temperatures in 1º increments.(Click on image for a larger view.)

Note that the ECMWF shows ‘cooler’ temperatures at the shore; this is an artifact and the result of the model I access is somewhat lower resolution and each grid point covers a wider area that spans over the ocean and over the land.

The Phillies are playing this afternoon!

Citizens’ Bank ParkBlue Bell
Actual Temp 2 PM100.199.3º
Heat Index 2PM 112.4º108.9º
Wet Bulb Globe Temp92.591.3

There appears to be no chance of thundershowers or rain today.

Forecast Update

Posted Wednesday 07/01/26 @ 5:30 PM — Today’s high at PHL airport was 97º. (The Model Blend forecast for today was for 97.7º± 2.2º The ECMWF forecast was for 97.1º) Dew points were in the mid 70s, making it feel much hotter.

For Thursday, the Model Blend forecast high is for 103.3º. The ECMWF forecast high is now ‘only’ 102.8º. Dew points will be lower, closer to 69º.

The latest RRFS is still forecasting some storms for early this evening just northwest of the city. (The HRRR is not.) The HRDPS has a few scattered storms, mostly in Bucks county and north. Current water vapor suggests the HRDPS might be correct.

5 PM Water Vapor (mid level) and Radar with 700 mb wind streams. (Click on image for a larger view.)
Wednesday Forecast Update

Posted Wednesday 07/01/26 @ 9:55 AM — Last night’s models continue with the similar temperature forecasts as previous runs; the trend is for somewhat hotter Friday and Saturday than Thursday!

A comment asked about heat relief from rain/thunderstorms.

Water Vapor image shows any upper/mid-level ‘triggers’ (upper level potential vorticities) for storms and Philadelphia doesn’t lie downstream in the upper air path of these disturbances—

Water Vapor image at 9 AM 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, (Click on image for a larger view.)

So there doesn’t appear to be any upper air triggers. However, there may be some triggers for storms at lower levels of the atmosphere.

Regarding pop-up storms, some may develop about 4-7 PM to our far west, according to Q-vector 700mb analysis of the RRFS data—

The Q-vector divergence over Philadelphia suggests that any storms that develop to our west may fall apart as they enter the area of divergence. (Click on image for a larger view.)

At even lower levels (850 mb) , there does seem to be a thermal energy trigger that may set off some storms—

06z RRFS theta-E 850mb frontogenic forcing at 6 PM may support pop-up storms about (Click on image for a larger view.)
Commentary:

As mentioned recently, over past months, I’ve been working with Claude AI and ChatGPT (mostly Claude) to develop Q-vector analysis and Frontogenic Analysis tools derived from the new RRFS model. I’ve been built them into my automated model download post-processing These tools are “derived parameters” and aren’t part of the model, but they are routinely used by meteorologists. Regular use is new to me and it will be a learning experience going forward when to apply these tools.

I’m gradually moving some of these post-processing tools to my downloads of the HRRR and Canadian HRDPS models.

Despite its newness, I’m not convinced that the RRFS is the best forecast model at this time for my efforts. As an example, the RRFS is forecasting high temperatures today that are way too cool (-3-4º) compared to the HRRR, HRDPS, ECMWF, ICON, and GFS. There are known deficiencies with the RRFS and they are being addressed with a RRFS v2 that is not yet available.

So, in supplying these possibilities of thunderstorms here late this afternoon, based on these tools and the RRFS, I’m stepping out into new forecasting territory.

It’s Going to be Over 100º.
Why are they still talking about the Heat Index?

Posted Tuesday 06/30/26 @ 8:04 PM — I suppose this falls into the category, “Opinion – Commentary”.

I know the TV weather entertainers like to talk about the Heat Index. It’s often (but not always) higher than the actual temperature and it can make a typical 96º-98º summer temperature forecast sound very ominous. This week we have a high temperature forecast that is actually in the low 100s and it’s already ominous. It really doesn’t need any additional hype.

Use of the heat index this week is actually a disservice since it fails to distinguish this true health-threatening 103º forecast from a heat index of 103º-105º that you hear about at some point almost every summer.

Let me put this another way. Were you going to do a major work project outside on Thursday (Will the Phillies really play?) knowing there will be a temperature of 103º, but now, knowing the heat index is 110º, you’ve decided you’re not going to do the project? Let’s get real!

I’m posting this heat index map for Thursday. Has it just changed your mind about outdoor activity from the previous maps with actual forecast temperatures?

19z NBM “Apparent Temperature” aka Heat Index at 3 PM Thursday (Click on image for a larger view.)

There’s a new way of imparting dangerous temperature conditions that takes into account temperature, humidity/dew Point, wind and Exposure to heat of direct sun. It’s called the Wet Bulb Globe Temperature. It’s got the right idea, but the way it’s scaled in degrees F, it likely will never catch on.

Here’s the Wet Bulb Globe Temperature for Thursday—

Model Blend WBGT (wet bulb globe temperature) at 2 PM Thursday. It just doesn’t sound ominous enough, even though a 92 reading is considered extreme. But it’s a better measure of the impact of summer heat and sunshine. (Click on image for a larger view.)
Heat Wave Update

Posted Tuesday 06/30/26 @ 5:37 PM — Tomorrow, Wednesday will be a ‘normal’ very hot day for the first day in July. Highs 96º-97º. Not so for the rest of this week.

It should be noted that the model extreme heat forecasts have been extremely consistent over many days, leading to higher than average certainty. Here’s the latest available ECMWF forecast high temperature forecasts (around 4:30 to 5:00 PM each afternoon)—

12z ECMWF high temperature forecast for Thursday at 5 PM. Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)

Friday—

12z ECMWF high temperature forecast for Friday at 5 PM Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)

The above ECMWF might be too high, then again, maybe not. Here’s the latest Model Blend forecast Thursday—

18z NBM (model blend) 12 hour high temperatures. Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)

The above Model Blend Max Temp uses advanced statistical techniques. With the previous version of the model blend (NBM v4.3) I found that the high temperature PLUS standard deviation was more accurate in situations like these—

19z Model Blend Temperature with standard Deviation added. Fine Contours are near-surface (2m) temperatures in 1º increments. (Click on image for a larger view.)

The new Model Blend (NBM 5.0) Max Temp may have corrected this cooler bias. We’ll see.

Historic Heat Wave Potential

Posted Tuesday 06/30/26 @ 9:24 AM — The models consistently point to the potential for an historic heat wave over the next several days. The ECMWF-AI and the GFS continue to show actual temperatures in excess of 106º. The Model Blend (NBM), recently updated to version 5, has a good track record in forecasting high temperatures. (The previous version 4.3 tended to run a bit low.)

Here’s the current water vapor image—

Water Vapor image at 9 AM with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , GFS potential vorticity contours (violet fine contours), Note the position of the 576 thickness line, the demarcation of severe heat and humidity. (Click on image for a larger view.)


Here are the Model Blend High Temp Forecasts Wednesday-Friday:

06z NBM 12 hour mean high temperatures (Click on image for a larger view.)
06z NBM 12 hour mean high temperatures (Click on image for a larger view.)
06z NBM 12 hour mean high temperatures (Click on image for a larger view.)

Please note that the high temperatures this time of year often occur between 4 PM and 6 PM.

Saturday will see temperatures still over 100º from the city eastward.

Severe Heat Wave through Sunday

Posted Monday 06/29/26 @ 7:50 PM — A heat wave with temperatures 90 or above begins on Tuesday and will last at least through Sunday. High Temperatures Thursday through Saturday may set records.

We start with highs 90-91º on Tuesday.

ECMWF Thurs Highs
GFS Thurs Highs
CMC GDPS Thurs Highs
NBM Thurs Highs

The above temperatures forecast for Thursday (and some models have it hotter on Friday) are rarely seen forecast for this area. These temperatures are actual forecast temperatures, not heat indices.

The higher resolution NBM makes it clear that it will be very hot, even at the shore. (The lower resolution models obscure this.)

Monday Forecast Update

Mon 7:48 PM —Forecast Review —A few showers developed in Berks and Upper Chester counties, but nothing like the forecast from this morning’s RRFS and this afternoons RDPS.

Posted Monday 06/29/26 @ 9:46 AM — The boundary of the very hot humid air has not quite made it into our area, as shown by current wind directions and dew points-

RTMA current conditions (9:30 AM) dew points and wind directions. I’ve drawn the approximate position of the true tropical boundary. (Click on image for a larger view.

This morning’s water vapor image shows an upper air disturbance near the Great Lakes that will swoop down into our area this evening, pulling the very hot air closer to us—

Water Vapor image at XX with superimposed RAP model MSL pressure (black contours), 500-1000mb Thickness (yellow contours) , RAP potential vorticity contours (violet fine contours). The position of the 576 thickness is still southwest of us. The purple contours near the Great Lakes indicate upper air energy that may cause a few showers/thundershowers Monday evening. (Click on image for a larger view.)

The latest RRFS shows this upper disturbance above will cause some showers/thundershowers again Monday evening in some areas only.

RRFS (06z) forecast 1 hour rainfall at 9 PM Monday evening. The RRFS does not have these showers making it into NJ. (Click on image for a larger view.)

The RRFS did pretty well with its showers forecast Sunday night, actually under-forecasting the rainfall. We’ll see if it can do it again.

Originally Posted Sun 8:39 PM — Parts of the area received much-needed rainfall this evening, significantly more than had been forecast.

With the expected heat and humidity building this week, there’s always a chance of a storm in the afternoon, but often times, this sort of heat in the upper atmosphere ‘caps’ the storms. So this was likely our last chance for significant [somewhat] widespread rainfall for much of this coming week.

The severe heat expected to build this week has been well-advertised. As mentioned, in all the years of forecasting, I haven’t seen this sort of heat forecast here for at least 20-25 years.

Here’s the AIGFS forecast for Thursday with upper and lower level high pressure heat domes over us—

18z AIGFS forecast for Thursday 2 PM. notice the position of the orange-gold 760 thickness line which extends into Maine. It also shows a thermal trough may develop along the coast near us. (Click on image for a larger view.)

Here’s the latest Model Blend Temperature forecast- Incredible heat!

Model Blend Actual Temperature,Heat Index, Dew Point with standard deviations. (Click on image for a larger view.)

This week’s weather promises to be interesting. Stay tuned for updates.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx #PhillyWx

Sunday and Week’s Hi Temp Outlook

Posted Sunday 06/28/26 @ 9:09 AM — Several models have returned to a forecast of some showers/thundershowers northwest of the city and entering over to NJ. Here’s the latest REFS model snapshot for 6 PM and total rainfall, indicating its eastern extent of the forecast showers—

Rainfall at 6 PM
Total Rainfall

Severe Heat Thursday – Friday

I’ve been forecasting the weather a very long time. I’ve never seen forecast high temperatures as extreme for our area as what’s being forecast for end of this week. Here’s the latest ECMWF forecast highs about 5 PM Thursday—

00z ECMWF forecast high Temperatures about 5 PM Thursday (Click on image for a larger view.)

Here’s the Model Blend Mean Temp forecast for Thursday—

12z NBM just available. Mean High temperatures for Thursday. Note that the standard deviatioin is ±3º Per the ECMWF, these temps could be 3º hotter! (Click on image for a larger view.)

I’ll be dusting off the Wet Bulb Globe Temperatures and the Heat Index (Apparent Temperatures) this week.

Sunday Forecast Update

Posted Saturday 06/27/26 @ 8:17 PM — Sunday will begin cloudy, but clouds will thin towards noontime and most of the day will be sunny through varying amounts of mid and high clouds. Some models do show intermittent periods of low clouds in the afternoon. A northeasterly wind will keep temperatures in the low to mid 80s, but dew points will be in the noticeable upper 60s.

Today’s models are still showing widely scattered storms Sunday afternoon and early evening, but they will mostly stay north and west of Philadelphia.

Outlook-
Things become increasingly hot by Tuesday. By Wednesday, we’re approaching 100º. Thursday looks to be in the low 100’s!

19z NBM (model blend) highs at 2 PM. Actual high temperatures occur between 3-5 PM so these numbers are likely too low! (Click on image for a larger view.)
Forecast Update

Updated Friday 06/26/26 @ 10:41 PM — Tonight’s early models are showing more scattered popup thunderstorms/showers on Sunday than previously forecast. Details on an update tomorrow.

Originally Posted Fri 7:46 PM — As discussed earlier Friday, there had been a trend for the showers and rain to be mostly south of the Philadelphia area but today’s latest models no longer show that trend.

Low pressure moving along a somewhat stationary/warm front will bring showers and thunderstorms Saturday.

Current (4:41PM) 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.)
Saturday

Low pressure moving along the front will bring periods of showers, maybe a thunderstorm from early morning to late afternoon. Highs (Model Blend): Blue Bell- 78º Philadelphia 81º ±4.5º (Higher than usual uncertainty.)

Sunday

Mostly sunny through thin high cirrus clouds. An occasional period of cloudiness. Highs (Model Blend): Blue Bell- 83 º Philadelphia 86º ±4.0º Higher than usual sd and uncertainty.

Some scattered thunderstorm activity possible Sunday evening.

Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Friday -Saturday -Sunday

Posted Friday 06/26/26 @ 10:07 AM — The stalled front near us is moving back north as a warm front Friday morning. Very little activity is with this front. Expect showers to end in the area by noon but considerable mid-level cloudiness will remain through the day. It’s possible to see some dim sunshine through clouds early afternoon.

A disturbance moving in from the west will spark some showers and thunderstorms to our south this evening, mostly in Maryland/Delaware and South Jersey.

An interesting trend noted for Saturday. The AI models and the ECMWF maintain a forecast for rain in most of the Delaware Valley on Saturday, BUT many models (GFS, RRFS, RDPS) keep the rain mostly from the city and southward— Areas north and west of the city will have minimal or no rain, according to these models. Here’s a snapshot from the RRFS—


06z RRFS snapshot at noon keeps the rain/thunderstorms mostly from the city on southward on Saturday (Click on image for a larger view.)

This will be an interesting ‘experiment’ where the ECMWF shows considerable rain while the GFS has a different, southern track forecast. (spoiler: over the winter, the GFS did better than the ECMWF in these ‘contests’.) On the side of the ECMWF are the AI models (AIGFS and ECMWF-AI). So some northwestern areas may have better weather than currently forecast.

Stay tuned for my regular “Weekend Weather Forecast” later today.

Thurs Fri Sat Outlook Update

Posted Thursday 06/25/26 @ 2:44 PM — The weakening, cold front will drop through after midnight. Today’s models suggest a bit more shower activity will move in after midnight Thursday into very early Friday morning.

12z RRFS 1 hour precipitation at 6 AM Friday. (Click on image for a larger view.)

It should be noted that the REFS has considerably less rainfall for our area. Both models are new and I’m not able to evaluate this discrepancy.

Both models have the rain ending mid morning with cloud cover thinning Friday afternoon before the next system and warm front move in Friday evening as the warm front moves north and low pressure moves over us.

Saturday looks fairly cloudy and rainy. Sunday looks sunny warm and humid.

AIGFS forecast for Saturday at 2 PM. Hot humid air south of the 760 thickness line (500-1000mb thickness) (Click on image for a larger view.)
Thursday Friday Saturday Forecast Overview

Posted Wednesday 06/24/26 @ 7:46 PM — A weakening low pressure system in southern Canada will attempt to drag a weak front through late Thursday evening into Friday.

18z GFS surface forecast for 7 PM Thursday. Weak approaching front will dissipate as it moves towards us. (Click on image for a larger view.)

Most of Thursday will be sunny or sunny through high cirrus clouds. It will become cloudy after 6 PM as the front approaches. The showers will mostly be to our north and northwest around midnight. Very little rain expected in the city.

Friday will see some scattered showers in the morning but things will quiet down in the afternoon with some sun possible (?)

There’s some uncertainty about the location of the dissipating front for Saturday.

Some models(GFS, Canadian, AI versions) have it right over Philadelphia with some significant rain. The latest RRFS shows it south of the area, moving back as a warm front Saturday evening with thunderstorms. Too soon to be sure, but the AI models have rain for much of Saturday. Things clear by Sunday with more humidity.

Wednesday through Saturday Overview

Posted Tuesday 06/23/26 @ 9:56 PM — Here’s the latest MRMS rainfall totals for Monday night through Tuesday—

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.)

High pressure will build in for Wednesday and Thursday. A system approaches late Thursday into Friday possibly with some light rain, especially areas far north of the city.

Another system approaches late Friday into Saturday.

18z ECMWF-AI forecast for Friday at 8 AM. Friday’s system may stay to our north. There’s a question about how long the Saturday system will linger in our area. (Click on image for a larger view.)

Saturday may be a rainy day, according to the AI models with some predicting 1″ of rain. The regular models have this system moving out Saturday afternoon. Too early to be sure.

Tuesday Forecast Update

Posted Tuesday 06/23/26 @ 10:10 AM — More rain is expected today after much of the region (but not all) received a much-needed significant rainfall. Here’s the MRMS summary estimate of actual rainfall received over the prior 24 hours (9 AM)—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL RECEIVED from 9AM Monday to 9 AM Tuesday. . Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

Most models have light rain continuing until later Tuesday afternoon, tapering off from west to east about 3 PM- 5PM.

The southern Jersey shore may have some heavier rainfall later this afternoon. The models have a considerable range in additional rainfall with the AI GFS and ECMWF AI models in the 0.5“– 0.6″ range for the immediate PHL area. with the RRFS and HRRR showing considerably less. Based on current radar, I’m leaning towards the AI model forecasts.

Water Vapor image at 10:17 with superimposed RAP model Vertical velocity (yellow contours_with MRMS Radar and NexRAD radar Note the area of strong upward vertical motion at the Jersey shore, (Click on image for a larger view.)
Tuesday – Another Rainy Day

Posted Monday 06/22/26 @ 7:44 PM — The second half of this system, as described earlier, will arrive Tuesday morning according to the HRRR and a bit later according to the RRFS. There had been a question of when this system would exit and Sunday’s ECMWF-AI model correctly identified it to last into Tuesday afternoon.

While the main placement of the rain has been north and south of our area, parts of the Delaware Valley have already received considerably more rainfall than had been forecast for the entire storm.—

6 PM 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.)

Additional considerable rainfall is expected with the next part of this system, a second low developing near the Virginia Coast—

18z AIGFS forecast for Tuesday at 2 PM showing 6 hour previous rainfall. Considerable additional rain expected tomorrow. (Click on image for a larger view.)

The latest RRFS shows heavy rain and storms again about 3 PM Tuesday afternoon. Rain will be ending much later in the afternoon—

18z RRFS simulated radar forecast for 3 PM Tuesday. Blue=low clouds, maroon=mid-level clouds, tan = high cirrus clouds
Where’s the Rain?

Posted Monday 06/22/26 @ 4:54 PM — That one thunderstorm cell (see previous radar below) blossomed into a swath of heavy rain that went through Center City, according to the 4 PM MRMS—

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)   12 hours Through 4 PM today. The center city accumulation occurred between 2-4 PM   (Click on image for a larger view.)

The rest of our area received the big goose-egg 0″.

More storms are developing to our southwest and northwest and will move through in the next hour or so.

4:52 PM Radar and MRMS radar composite with 700 mb wind streams (green) and vertical motion (omega- yellow contours) (Click on image for a larger view.)

So the forecast for thunderstorms between 2 and 4 PM held for the city, but it’s looking like my Q-vector analysis forecast based on the RRFS model promising a rain-free early start to the soccer game may not hold very long.

Monday Update

Posted Monday 06/22/26 @ 1:45 PM — The latest REFS has the heaviest rain accumulation to the north and the south of Philadelphia by Tuesday evening. This scenario was supported by several models yesterday.

12z REFS shows the heaviest rain accumulation north and south of our area by 9 PM Tuesday. Much of the heavy rain occurs on Tuesday late morning to mid afternoon. (Click on image for a larger view.)

Posted Monday 06/22/26 @ 1:38 PM — Storms are developing to our west, on our doorstep, and the dynamics favor rapid intensification of some of these storms.

New strong cell developed in place ( 1:35 PM) as this area moves into favorable upward motion

Here’s the latest RAP model “SWEAT” index (Severe Weather Event and Threats) with values exceeding 400 in some areas—

RAP model boxed areas show SWEAT index into the severe range (>400) over NJ by 4 PM. (Click on image for a larger view.)

The latest RRFS has backed off on the some of the accumulating rain for today and still shows a significant rainfall for Tuesday mid-day.

Monday Storms Update

Posted Monday 06/22/26 @ 9:06 AM — The system approaching our area is complex and several models show it moving in as two separate but related systems, one later today and another early Tuesday morning. The models still have the largest rainfall to our north.

Today’s 06z ECMWF-AI model forecast for 8 PM Tuesday. Two low pressure centers with rain lasting into the early afternoon. (Click on image for a larger view.)

The focus today has been on thunderstorms that may affect the soccer match later this afternoon. Based on the latest RRFS model, (06z) it appears the heaviest thunderstorm activity this afternoon will be between 2 PM and 4 PM near the city.

As mentioned in a few recent posts, I’ve been using AI to assist with advanced model calculations “tools” for predicting rain and storms. Today is a perfect time to unveil them.

The latest RRFS shows the greatest amount of forcing and dynamics around 2-4 PM today (Q-vector analysis and dynamic vertical motion) —

RRFS Q-vector analysis at 3 PM shows a moderate level of upward motion upstream from the city (orange coloration) with spotty humidity and strong vertical motion in the areas that are red and black. Strong storms over parts of the city at 2-4 PM (Click on image for a larger view.)

Of interest is the Q-vector analysis at 6 PM, showing inhibition of storms over the city.

RRFS Q-vector analysis at 6 PM. Large area of divergence and downward motion (inhibits storms) near the city after the storms departed, which have moved into northern NJ. (Click on image for a larger view.)

The summary statement- based on the above, it’s possible that the soccer game, at least through 5 PM to 8 PM will not be impeded by rain/storms.

While I probably would have better odds betting on the game today rather than betting on my new approach to forecasting with the RRFS, we’ll see how it all works out.

More storms tonight and especially after midnight into Tuesday morning.

Updates later today. Stay tuned.

Update

Updated Sunday 06/21/26 @ 7:00 PM — Over the past two hours, the latest GFS and RRFS models have become available. They show a strong trend towards the rain lasting well into Tuesday (early afternoon) with total rainfall near or above 1” and 2-3 inches in localized areas.

Originally Posted Sun 5:03 PM — The beautiful weather from this weekend will quickly be replaced with clouds Monday morning and then showers and thundershowers as early as the noon hour. (More widespread activity waits for the evening.)

There’s a considerable range of forecasts with this system and the series of graphics that follow demonstrate this—

A strong system currently in the central US will move eastward and affect our weather early Monday with more humidity.

Water Vapor image with superimposed RAP model parameters and radar at noontime Sunday. The warm front will move north of our area Monday and rain associated with this system. Note the fine violet contours near the main low- areas of jet level potential vorticity which will keep this system powerful. (Click on image for a larger view.)

By noontime Monday, light scattered showers will be breaking out in and around Philadelphia; the heaviest rain remains far north and west—

CMC-GDPS wiith AI spectral nudging forecast for 12 PM Monday. Yellow-green is convective precipitation (thunderstorms) (Click on image for a larger view.)

At this point the CMC-GDPS AI diverges from the GFS and ECMWF models and I’ll use the latter two models from this point forward. The CMC-GDPS has the low moving out to sea; the GFS and ECMWF have secondary areas of low pressure with lingering heavy rain—

ECMWF forecast for 8 PM Monday shows heavy rain and thunderstorms over our area. The GFS is similar to the ECMWF. (Click on image for a larger view.)

By Tuesday morning, the GFS still maintains rain into the early morning hours. The ECMWF and CMC-GDPS has the rain offshore with some gradual clearing.

18z GFS forecast for 9 AM Tuesday morning. Lingering showers. (Click on image for a larger view.)

The slower GFS (more rainfall) looks pretty good because the latest ECMWF-AI model is even slower with the exiting rain, with it lasting into Tuesday afternoon—

12z ECMWF-AI forecast for near 8 PM Tuesday evening. Rain lingers with the ECMWF-AI even longer than with the GFS. (Click on image for a larger view.)

So, this will either be a fast-moving system with unimpressive precipitation or it will be a soaker with lingering rainfall well into Tuesday afternoon.

While heavy rainfall for our area was originally forecast with this system, today’s trends seem to be keeping the highest rainfall totals far north of our area, mostly in NY and north.