THIS WEEK’S WEATHER

Friday and Weekend Outlook

Posted Thursday 07/10/25 @ 5:40 PM — It’s been raining along the central NJ Shore much of the afternoon, as expected, the rain did not make it northwestward into Philadelphia. (The REFS over-predicted a northwestward extent.)

The Friday and the weekend looks to be drier than past days. Low clouds and patchy fog early Friday morning will give way to sunshine. An easterly wind flow will keep temperatures in the mid to upper 80s on Friday but it will still be humid with dew points in the low 70s.

Some models have widely scattered pop-up storms late afternoon and early evening Friday; most areas dry.

Saturday may have some low clouds in the morning, breaking way for sunshine through high clouds by late morning and afternoon. There’s a chance of scattered thunderstorms Saturday evening, especially further west from the city.
Sunday may have considerable cloudiness and some showers/thunderstorms to our west in the afternoon as a warm front takes shape to our south.

I’m using the term “may” here in my forecast for a reason— the weather pattern is quite diffuse and with the high humidity, any random triggers that develop can make a ‘dry’ forecast go bad.

Additionally, the weekend’s easterly/southeasterly wind flow will bring some uncertainty to the forecast regarding temperatures and the potential of wind convergence causing showers.

Things may clarify by tomorrow.


Thursday Forecast Update

Posted Thursday 07/10/25 @ 11:09 AM — This morning’s REFS does show some shower/thunderstorm activity somewhat further north, into Philadelphia, by this evening. Pop up storms possible later in the afternoon.

06z REFS forecast rainfall through 8 PM Thursday. (Click on image for a larger view.)

Posted Thursday 07/10/25 @ 8:23 AM —A quasi-stationary frontal boundary remains over our area. Moisture moving up from the southwest will result in considerable cloudiness, but with the lack of sunshine, instability from daytime heating will be reduced. That means less chance of showers and thundershowers today, especially from northern parts of Philadelphia and northward.

8 AM Current satellite water vapor image with superimposed RAP model 500-1000 mb thickness lines (yellow), jet level wind streamlines (orange contour-arrows) potential vorticity (fine violet contours) and superimposed MRMS radar. Areas in northwest PA have broken out into sunshine, but our area remains in the moist flow near the frontal boundary. Eventually by Friday and the weekend, the back edge of the moisture will move eastward. (Click on image for a larger view.)

The current Canadian GDPS with “AI Spectral Nudging” captures the northwest extent of the showers today—

00z GDPS with “AI Spectral Nudging” shows convective precipitation (yellow green) and clouds (grey black) at 2 PM. The northwest extent is very close to the REFS and only shows clouds northwest and west of the city. While not showing at 2 PM, much of S Jersey will see more showers and thunderstorms (Click on image for a larger view.)

Here’s the latest past 72 hours MRMS precipitation estimate—

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.)
Wednesday’s Storms Update

Posted Wednesday 07/09/25 @ 11:38 AM — The latest HRRR (12z) and REFS/RRFS (06z) are available. The storms and rain will follow a similar timing as Tuesday, with some rain and storms popping up in western suburbs as well as South Jersey by 3-4 PM.


Additional storms form and move across the area from 4 PM through 1 AM Thursday morning. The heaviest activity will be just south and east of the city, near Swedesboro and Bridgeport NJ.

06z REFS total rainfall forecast. The heaviest rain will fall in the areas of the strongest storm activity. The white arrow is the expected path of the storm activity. (Click on image for a larger view.)

Let’s jump right to the “Severity Comparison Chart”

Severity Parameter
(HRRR)
Sept 1 , 2021
Tornado Outbreak
(example of highly severe)
Recent
4-1-23
Tornadoes
(Example of severe)
Yesterday
 07-09-25
Tornadoes

Today
07-09-25

12z
HRRR
&
Impact

Notes
CAPE
Joules/kg
3500-4200
⚑⚑⚑⚑
2100
⚑⚑
2680
⚑⚑
3650
⚑⚑⚑⚑
S Jersey
Helicity
m^2/s^2
1350
⚑⚑⚑⚑⚑
655
⚑⚑
403
360
 
Vertical Shear
1/sec
40-46
⚑⚑⚑
40-45
⚑⚑⚑
20
32
⚑⚑
 
Precipitable Water 2.7″
⚑⚑⚑⚑
0.83”
2.6″
⚑⚑⚑⚑
2.6″
⚑⚑⚑⚑
Heavy rain potential
Lifted Index
º K
minus 6º
⚑⚑
minus 9.3º
⚑⚑⚑
Minus 8.3º
⚑⚑
Minus 8.2º
⚑⚑
 
HRRR Hail
inches
1.9
⚑⚑
1.4
1.8
⚑⚑
1.7″
⚑⚐
 
Peak Wind Gusts
mph
40-50
⚑⚑
40-50
⚑⚑
51.6mph
⚑⚑
35-41mph NJ area
Storm Motion Shear Vector
Alignment
Aligned – ~ 90º
⚑⚑
Almost aligned
⚑⚑
Somewhat aligned
Poorly 
aligned
 
250 mb
Jet Stream Wind
mph
63
135
⚑⚑
41
61 
 
Severity Parameters Impact: ⚑ indicates favors Severity ⚐ indicates Possible Severity
↓ indicates works against Severity ⇩ Significant, but less impact


Many of the severity parameters are similar to those yesterday and it will be difficult to predict in advance whether the storms will be as severe. With temperatures lower and less sunshine today, my guess is for the storms not to be quite as bad. But these things are difficult to predict. There’s more jet stream energy today and much more vertical shear, making it more likely that any storms will maintain their punch.


Wednesday’s Storms

Posted Wednesday 07/09/25 @ 8:38 AM — Just enough time this morning for a quick update. Yesterday’s short wave pulled down a indistinct frontal boundary to just south of Philadelphia.

Several waves will develop along this boundary, causing thunderstorms to again develop and move through. The main area today will be Philadelphia and just south. Northern suburbs may not see much activity. Chester, Delaware counties and southern NJ will be the main target areas to watch. Heavy rain again a possibility.

00z REFS forecast for 4 PM (1 hour rainfall forecast) Meaning that this precipitation starts between 3 and 4 PM. (Click on image for a larger view.)

I’ll update later this morning with new models.


Tue 7:12 PM —Forecast Review — The storms that came through this evening were impressive and stronger than I would have guessed based on forecast severity parameters which were high in CAPE and Precipitable Water (PWAT) and Lifted Index. and somewhat middle of the road in Vertical Shear and Helicity. (All based on the HRRR forecast values.) As mentioned yesterday, the trigger was a “potent” short wave.

However, my update (below) posted at 3:51 PM showed very impressive vertical motion ahead of the line of storms to our west, and the greater strength of the storms was less of a surprise when they moved in.

Several tornadic signatures showed on radar. Here’s one that was impressive in upper Montgomery county—

This PHL Terminal Doppler Radar (courtesy of Weathertap.com) shows a likely tornado in the white box, based on radar signature. (Click on image for a larger view.)

Another tornadic signature in eastern Montgomery county may or may not be an actual tornado.—

This PHL Terminal Doppler Radar (courtesy of Weathertap.com) shows a possible tornado in the white box, based on radar signature. (Click on image for a larger view.)

What was really impressive was the experimental REFS model which was accurate with its timing of the lead storms in Philadelphia and the subsequent storms that are still lingering. The HRRR, our current high resolution operational model, really got the timing of today’s storms wrong.

The REFS is scheduled to become operational in early 2026, if NOAA is allowed to do its wonderful job. The REFS and the RRFS will be replacing several older, less-skillful “legacy” models such as the NAM and HREF and HIRESW-ARW models.

More about this on my RRFS page.

“Tracking” Storms?? What does that really mean??

As I’ve said here before, I avoid the using the expression “tracking” the storms. The TV people use this all the time. Storms, and especially thunderstorms, are dynamic processes. They can form at a point almost instantly. They’re not a train that arrives at a scheduled time. There’s nothing to “track”. Case in point are the storms that just formed over Center City after 4 PM.

PHL Airport Terminal Doppler Radar at 4:10 PM Click to animate (Click on image for a larger view.)

The appearance of these storms between 4-5PM suggests the REFS is doing a great job with thunderstorms.


Tuesday’s Storms Update

Posted Tuesday 07/08/25 @ 3:51 PM — At 3:45 PM, radar and hourly updated RAP model shows a line of storms far west of the city with significant upward vertical motion (vertical velocity pressure, Omega) ahead of the line. This signifies likelihood of significant strengthening of storms as they approach our area—

Radar 3:45 PM with RAP model Omega overlay. Significant vertical upward motion predicted ahead of the storms (X) suggests likelihood of intensification. (Click on image for a larger view.)

The latest REFS (experimental) shows some storms develop here as early as 5 PM, but the main batch of storms arrive near the city between 6 and 8 PM.

12z REFS 1 hour rain and standard deviation (contours) at 5 PM Not sure if this is still forecasting a bit early. (Click on image for a larger view.)

For comparison I’ve resurrected an old table with some significant storm histories. The highlighted column is today’s severity parameters and allows you (and me) to compare with today’s values.

Severity Parameter
(HRRR)
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
07-08-25
Today’s
18z
HRRR
&
Impact

Notes
CAPE
Joules/kg
3500-4200
⚑⚑⚑⚑
2100
⚑⚑
2600
⚑⚑
2680
⚑⚑
Helicity
m^2/s^2
1350
⚑⚑⚑⚑⚑
655
⚑⚑
726
⚑⚑
403
Vertical Shear
1/sec
40-46
⚑⚑⚑
40-45
⚑⚑⚑
30
20
Precipitable Water 2.7″
⚑⚑⚑⚑
0.83”
2.1″
⚑⚑

2.6″
⚑⚑⚑⚑
Heavy rain potential
Lifted Index
º K
minus 6º
⚑⚑
minus 9.3º
⚑⚑⚑
minus 9.9º
⚑⚑⚑
Minus 8.3º
⚑⚑
HRRR Hail
inches
1.9
⚑⚑
1.4
1.8
⚑⚑

1.8
⚑⚑
Peak Wind Gusts
mph
40-50
⚑⚑
40-50
⚑⚑
65mph
⚑⚑
51.6mph
⚑⚑
NJ area
Storm Motion Shear Vector
Alignment
Aligned – ~ 90º
⚑⚑
Almost aligned
⚑⚑
aligned
⚑⚑
Somewhat aligned
250 mb
Jet Stream Wind
mph
63
135
⚑⚑
74
41
Severity Parameters Impact: ⚑ indicates favors Severity ⚐ indicates Possible Severity
↓ indicates works against Severity ⇩ Significant, but less impact

I just want to add that the HRRR shows the heaviest storms moving north and south of the immediate PHL area. Not true of the REFS and RRFS. Something to watch.

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 suggest following me on mastodon.social or bluesky.social


Tuesday’s Storms Update

One More Thing: the latest Canadian GDPS “with AI nudging” also suggests earlier timing, as early as 4PM, similar to the REFS below.

Posted Tuesday 07/08/25 @ 7:28 AM — A potent short wave and front will move through Tuesday evening. Ahead and along with this disturbance will be strong dynamics that promises more wide spread heavy rainfall and the potential for somewhat more severe storms than Monday.

In terms of timing, the REFS (experimental) still shows some showers/storms as early as 3-5 PM in the western suburbs, then moving eastward. The latest RRFS (experimental) continues to be about two hours later, with storms approaching the immediate PHL area around 6-7 PM.


The latest HRRR shows storms approaching the immediate PHL area around 6-8 PM, somewhat earlier in western suburbs.

06z HRRR forecast “simulated radar” at 8 PM Tuesday. (Click on image for a larger view.)

In terms of severity, greatest likelihood is in western sections about 5-7 PM. Heavy rain possible throughout the area.


Tuesday Storms

Posted Monday 07/07/25 @ 7:59 PM — Just wanted to add that the GFS shows some storms in Harrisburg moving through our area around midnight. Not shown in REFS or RRFS forecasts for tonight (Monday).

Posted Monday 07/07/25 @ 7:33 PM — The storms developed in many (but not all) areas around Philadelphia this afternoon. Here’s the MRMS rainfall totals—

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.)

Tuesday should be mostly sunny hot and VERY humid again. A slight dip in the jet stream and a potent ‘short wave’ will approach, causing the development of widespread showers and thunderstorms beginning about 4 PM. Additionally, we’ll be near the right entrance region of a jet streak, enhancing available energy.

The latest GFS shows this potent area of upward motion around this short wave.

18z GFS forecast for 5PM showing strong concentration of upward vertical velocity pressure. Strong, possibly severe storms are possible. (Click on image for a larger view.)

The REFS did well today and I’ll stick with its forecast for Tuesday.

12z REFS forecast rain with standard deviation (contours) at 6 PM Tuesday. (Click on image for a larger view.)

The REFS has showers breaking out west of the city as early as 3 PM, but widespread showers and thunderstorms are expected by 4-6 PM.

(It should be mentioned the the latest RRFS has the storms moving in about 2 hours later than the REFS shown above. )

Several hours of widespread rainfall are expected with storms moving into NJ by 5-6 PM. Localized areas of 1-3″ of rain expected. Unlike today’s storms which were mostly heavy rain, Tuesday’s storms will have somewhat higher vertical wind shear and areas of elevated helicity. Some severe storms possible, especially into South Jersey and Delaware.


Monday Update

Posted Monday 07/07/25 @ 10:10 AM — The moisture associated with the remnants of tropical depression Chantal have started to move across our area today. Any sunshine will induce instability and thunderstorm formation. Here’s the latest REFS hourly rain forecast at 1 PM, 3 PM and 5 PM today—

06z REFS hourly rainfall with standard deviation (contours) 1 3 5 PM today. (Click on image for a larger view.)

Most of the activity will be in the afternoon hours and taper off by 9 PM.

Showers will be scattered, but any storm will be slow moving and capable of dropping heavy rainfall. Precipitable water forecasts are as high as they get around here, 2-3″ – 2.5″ in some areas. Flooding type rains are possible.

RRFS forecast precipitable water at 4 PM. As high as they get outside of the tropics. (Click on image for a larger view.)

Originally Posted Sun 5:37 PM —The remnants of tropical depression Chantal are located in North Carolina and the moisture and energy of this weak system is expected to move over our area on Monday.

5 PM 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. Current position of CHANTAL is indicated as {L} (Click on image for a larger view.)

Some showers are breaking out in Delaware at this time (Sunday evening) and some showers may make into Delaware County and just south of the city by 8 PM.

More numerous showers and thunderstorms will develop on Monday. Shear and helicity values are weak. The main issue with these showers and storms will be the possibility heavy, slow moving rainfall. The showers will be scattered.

For Monday, a few scattered showers are possible in the morning, but the real deal will be during the afternoon where daytime heating will induce these showers and storms. 2PM to 8 PM will be the likely time slot with showers peaking around 4PM – 5 PM Monday. It will be warm (mid 80s) and VERY humid.

Here’s the latest REFS forecast for 5 PM

12z REFS forecast for 5 PM Monday. Previous 1 hour precipitation with standard deviation (contours)(Click on image for a larger view.)

Daytime hours on Tuesday look to be dry until about 4 to 8 PM, when showers and storms move in from the southwest. It will be very warm and VERY humid on Tuesday


WEEKEND WEATHER FORECAST

Sunday Forecast Update

Posted Saturday 07/05/25 @ 5:43 PM — Sunday looks to remain sunny, but an increase in temperatures and humidity will become apparent by early afternoon. High temperatures will approach or exceed 90º and some areas from Center City to northeast into NJ may see highs in the 92º – 93º range. Dew points will approach or exceed 70º in some areas.

The approaching tropical system moisture (described in the earlier posting) and the developing thermal instability may cause some isolated/widely scattered showers/thundershowers to develop between 4 PM and 9 PM. Forecasting the exact placement and timing is never possible, but areas near Wilmington DE and in Chester County are likely areas.

The REFS (experimental) has been doing pretty well with these forecasts. Here’s what it’s showing at 8 PM—

12z REFS 1 hour rain with standard deviation. Forecast hour 8 PM. (Click on image for a larger view.)

Monday is looking humid, warm and wet due to the approaching subtropical system. Stay tuned.


Originally Posted Fri 5:24 PM —You don’t need me to tell you today was a spectacular Fourth of July, weather-wise. Low humidity, comfortable near-average temperatures, and sunny skies!

We’ll have this great weather through the balance of this weekend. The noticeable difference by Sunday will be higher temperatures and somewhat higher humidity.

Saturday Forecast

Sunny. Comfortable.

NBM high temperatures: Blue Bell, PA 86.8º ± 0.6º Philadelphia, PA 88.3 ± 1.5º
Average Uncertainty (based on standard deviation)

Sunday Forecast

Sunny. Slightly more humid. Somewhat breezy in the afternoon.

NBM high temperatures: Blue Bell, PA 90.2º ± 1.2º Philadelphia, PA 91.0º ± 1.7º
Average Uncertainty (based on standard deviation)

Beyond this Weekend

Of interest is a developing low pressure system with tropical characteristics (a warm center low) developing near Jacksonville FL. This will move up the coast Monday into Tuesday with rain, possibly heavy. The AI models are similar, but the track inland or somewhat more eastward is still to be determined.

ECMWF-AI model expected to move up the coast Monday into Tuesday. Possible heavy rain and high humidity expected. (Click on image for a larger view.)

THIS WEEK’S WEATHER

Thursday Evening Update

Posted Thursday 07/03/25 @ 6:11 PM — As forecast this morning, much of the energy and moisture for thundershower formation is north of our area.

Here’s what it looks like at 6 PM—

6 PM RADAR with RAP model vertical velocity pressure (omega) in green contours. There are two areas of strong vertical motion to our west, but what appears to be lacking is moisture. (Click on image for a larger view.)

The latest REFS still shows some showers here around 8 PM, but it might be over-forecast.

Experimental REFS (12z) 1 hour accumulated rainfall at 8 PM. Possibly overdone. (Click on image for a larger view.)

The Fourth of July Weekend is looking quite nice, sunny but increasingly warm. Near 90º on Saturday, low 90s and more humid on Sunday.


Thursday & Fourth of July Extended Weekend

Posted Thursday 07/03/25 @ 9:38 AM — A front will move across the area with an upper level trough Thursday evening. Most of the energy and moisture will move to our north. Compared to recent thunderstorms, precipitable (cloud water) will be in the 1.4″ range compared to 2.1″ in recent storms, so rainfall amounts will be lighter.

With the exception of New Jersey, which may see some isolated storms this afternoon, the area of showers and storms moves through the immediate Philadelphia area between 7PM and 11 PM, with the latest REFS leaning towards 9-10 PM —

06z REFS 1hour prior rainfall with standard deviation (contours) at 10 AM (Click on image for a larger view.)

The Fourth of July Weekend is looking quite nice, sunny but increasingly warm, especially by Sunday.

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 forecast postings, I suggest following me on mastodon.social or bluesky.social


Wed 9:30 AM —Forecast Review — Rainfall over the past several days was impressive, exceeding all model estimates. More amazing is the fact that we couldn’t get much of any rain here at all just a year ago.

Here’s the latest MRMS rainfall estimate over the past 72 hours. (It’s still raining in eastern NJ, so these numbers aren’t final.

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) Time period is 72 hours back.      (Click on image for a larger view.)

What difference does a year make? Last year at this time, we were ascending on the solar cycle curve, something well-studied and associated with decreased rainfall.

This year, we’re descending on the same cycle curve, having peaked a few months ago. We’ve just passed the solar maximum of this cycle. This climate change is especially prominent over periods of two solar cycles– the double cycle is called the Hale Cycle (The Hale Cycle refers to the magnetic polarity of sunspots that reverse every two solar cycles). Is this Hale Cycle the reason for last season’s drought and our recent rainfall pattern change? Maybe.

Wednesday Update

Posted Wednesday 07/02/25 @ 9:51 AM — The models still show lingering rain in eastern NJ while clouds are expected to thin and break for some sun from west to east about 12 -3 PM

00z GDPS with “AI Spectral Nudging” forecast for 3 PM Wednesday (Click on image for a larger view.)
Wednesday Forecast

Posted Tuesday 07/01/25 @ 7:37 PM — The cold front hangs up along the coast as weak waves of low pressure move up along it. Expect additional light showers this evening and overnight into Wednesday morning. The sun will break through clouds from west to east on Wednesday afternoon.

Here’s the REFS cloud level forecast at 2 PM Wednesday

REFS cloud forecast for 2 PM Wednesday. Clouds hang tight along the shore, but sunshine increases from west to east during the afternoon. Some isolated showers possible in NJ and along the coast. (Click on image for a larger view.)

Tuesday Forecast

Posted Tuesday 07/01/25 @ 7:49 AM — Multiple rounds of showers and thunderstorms gave our region significant rainfall in some areas—

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)   24 hour totals shown.     (Click on image for a larger view.)

A cold front moving through today. Some differences in the timing of the frontal passage with the HRDPS having the front move through about 4-5 PM, while the GFS has the front moving through about 8 PM with the showers and thunderstorms moving in 4:30PM to 7 PM

Similarly, the HRDPS has some showers moving through as early as 1 PM, especially just east of the city. The main line of showers and thunderstorms move through 3 PM -6 PM.

Based on yesterday’s model performance, I’m leaning towards the REFS and HRDPS which has showers and thunderstorms beginning at 3:00 PM to 4:30 PM, with some scattered activity possible as early as 1-2 PM mainly east of the city.

00z REFS forecast preceding 1 hour rainfall at 4 PM (Click on image for a larger view.)

All models have rain and thunderstorms continuing through the evening and night as low pressure develops along the front. Some rain may continue into early Wednesday morning. Heavy rain is expected.

Some thunderstorms may be strong to severe, but current forecasts of helicity and vertical wind shear are in the low- moderate range only.


Tuesday Forecast

Posted Monday 06/30/25 @ 5:41 PM — Showers and thunderstorms moved in from the south between 2:30 PM and 4 PM.

Towering cumulonimbus clouds about 2:20 PM Looking southeast along the Schuylkill bike trail. (Click on image for a larger view.)
Current Radar composite at 5:32 PM. Additional activity in Maryland may not make it here. The REFS shows some additional activity here about 2 AM Tuesday morning. (Click on image for a larger view.)

Very few of this morning’s models accurately predicted the timing and location of this afternoon’s storms. I always like to look back and see if any specific model did well. The HRRR, our best high resolution model, didn’t perform too well today, nor did the NAM-NEST. (The AI models don’t have the high resolution needed for thunderstorms.)

Looking back, the Canadian high resolution model (HRDPS) did reasonably well. The experimental REFS also did surprisingly well.

So with that, the REFS becomes “the model of the week”. It is currently forecasting showers/thunderstorms to return between 3 and 5 PM Tuesday afternoon. Some may be strong to severe. Stay tuned.


Monday Forecast Update

Posted Monday 06/30/25 @ 9:07 AM — Yesterday’s Model Blend (NBM) proved to be correct about the lack of showers this morning, and I’ll stay with the NBM for today’s forecast, with individual models showing a range of forecast times for showers and thunderstorms.

Pop up storms can occur anytime after 1 PM today with peak activity between 5 PM and 8 PM.

The latest NBM shows activity near the city picking up about about 1-2 PM just east of the city.

06z NBM prior 1hour rain forecast for 2 PM today. Location placement is almost never exact. (Click on image for a larger view.)

A considerable increase in coverage will occur later in the afternoon. Some areas may receive heavy rain in a short period of time.

Likely focus of heavier storms will be central areas of South Jersey in the mid afternoon and areas north of the city in the late afternoon.


Originally Posted Sun 8:50 PM —The ‘cold’ front that moved through Saturday has stalled just to our south and thunderstorms have been breaking out in South Jersey for much of Sunday, especially near the Delaware Bay and Cape May.

The front will return as a warm front on Monday. Large differences in the forecast exist for Monday morning. The AI version of the ECMWF and the latest GFS have scattered showers breaking out early Monday morning, while the regular ECMWF, the AI version of the Canadian GDPS keeps us dry until 2-4 PM.

The experimental RRFS has scattered pop-up storms in the morning; this may be an example of its tendency to over-forecast convective rain.

22z RRFS

The ECMWF-AI has so much precipitation and clouds in the morning that it keeps our high temperatures in the mid to upper 80s instead of the low 90s forecast by the drier forecasts.

The model blend (NBM) keeps us dry Monday morning as well, and I’m leaning towards its forecast. Its high temp in Philadelphia is 90.5º

It’s a tough call.

The models all come together by Monday afternoon with showers and thunderstorms popping up anytime between 1 PM and 4 PM and continuing into the evening. Peak time is about 6 PM according to the NBM.

Tuesday looks even more interesting, as a cold front moves into very moist and unstable air over the Philadelphia region. Stay tuned.


Weather… and Other Things 'Up in the Air'