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Sunday Rainfall Totals

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Weather Update

Updated Sun 07/09 @ 4:04 PM— Far western suburbs have been having heavy rain most of this afternoon. The rain with embedded thunderstorms is slowly moving in our direction and should be in the immediate Philadelphia around 5 to 6 PM with additional activity moving in from the south.

As had been forecast by several, but not all, models, the heaviest rainfall will likely be to our north and west.

The area of storms will depart our area by 10 PM, according to the latest HRRR.

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Weather Update

Updated Sun 07/09 @ 12:29 PM — Latest GFS model total rainfall is similar to last night’s general model forecast —

This morning’s GFS and HREF still have the period 3 PM through 8 PM as producing the highest rainfall rates in the Philadelphia area and immediate suburbs.

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Weather Update

Updated Sun 07/09 @ 11:10 AM — Thunderstorm activity has broken out way ahead of model forecasts, including . The complexity of this weather setup suggests last night’s models are not handling it accurately.

Some of this morning’s models are much faster with the precipitation entering and leaving our area.

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Sunday Heavy Rain Potential

Updated Sun 07/09 @ 9:15 AM — A complex system is approaching our area with strong jet stream energy and several impulses expected to affect us Sunday into Monday.

The complex system is shown via this morning’s water vapor image —

The models continue to place the immediate Philadelphia area in a “doughnut hole” where heaviest precip seems to be missing, but I’m going to chalk that up to some modeling error at this time.

Showers and thunderstorms can break out any time early this afternoon, but peak time for rain and thunderstorms is about 3 PM to 10 PM. There isn’t much signal for any tornadic activity and excessive, heavy rainfall appears to be the main threat. Areas far south and far north of Philadelphia will have the most activity.

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Sunday Forecast

Update Sat 7/08 10:55 PM — Some areas today received heavy rainfall with the thundershowers that popped up reasonably close to the model forecasts.

For Sunday, a few scattered showers possible in the morning, but most models have the main area of showers and thunderstorms moving in between 3 PM and 5 PM.

Of interest, tonight’s models have the heaviest rain missing the immediate Philadelphia area and surrounding suburbs.

Updates Sunday morning.

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Saturday Forecast Update

Updated Sat 07/08 @ 9:18 AM — This morning’s 06z models continue with a forecast of fairly widespread pop-up showers today in the immediate Philadelphia area and Delaware Valley.

These pop up showers/thundershowers will start as early as 1- 2 PM in and around the city and will persist until at least 8 PM. Rainfall in some may be heavy. PWATs will be in the 1.7″ to 1.9″ ranged. Here’s the latest HREF model with the forecast locations at 4 PM—

The latest trend with the rain on Sunday is for the heavy rain to move in mid afternoon (3 PM) from the west into the the early evening hours. This is about 3 hours later than previously forecast.

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Previously Posted Fri 7:59 PM —

Western areas had some fairly heavy rain Friday afternoon, but as had been suggested, the showers barely made it into Philadelphia.

Saturday will be similar to Friday with clouds giving way to a mix of sun and clouds. Thunderstorms again in the afternoon and evening hours. Details below.

A significant jet stream induced wave will bring stormy conditions for Sunday. An developing upper level large scale trough and a potent jet stream impulse will cause low pressure to develop. Significant lift will result in heavy rain.

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Friday’s Weather

Updated Thu 07/06 @ 8:19 PM —A few thundershowers popped up in Reading and Allentown this afternoon, with a few others in Montgomery and Bucks counties—

Some fog is possible Friday morning.

The weak frontal remnant will be a focus of greater coverage of thunderstorms late Friday afternoon and evening, mostly in far northwestern suburbs. It’s unclear how far the storms will travel eastward into the Philadelphia area late tomorrow, but several models have them falling apart. The ECMWF and HRDPS has some heavy rain that makes it into the immediate suburbs.

I’ll need to update tomorrow morning.

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Thursday’s Weather

Updated Thu 07/06 @ 8:33 AM — Expect similar widely scattered thunderstorms to pop up again today, somewhat more westward than yesterday’s showers. The models are relatively consistent with the placement of these thundershowers. They can occur any time between 2 PM and 9 PM today, most likely time frame is 4-7 PM.

HREF forecast placement of today’s thundershowers—

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Upcoming Weather Thur-Sun

Updated Wed 07/05 @ 7:59 PM —Satellite Water Vapor images can provide the visual clues into model forecasts, and of course, the models incorporate upper air data from these images for their forecasts.

The current pattern of scattered afternoon thunderstorms is being driven in part by a small upper air cyclonic trough (1 below) over Pennsylvania. More info in the caption below—

Widely scattered thunderstorms expected again Thursday afternoon and early evening. These will mostly be in the western suburbs of Philadelphia, possibly extending into the city. More widespread showers and thunderstorms likely later Friday. Heavy rain possible Sunday.

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Wednesday Weather

Updated Wed 07/05 @ 11:29 AM — High humidity and some weak upper air disturbances will cause scattered thunderstorms to develop any time from 2 PM through about 8 PM. Low vertical shear will cause any pop up storms to collapse under their own downdrafts.

The latest HREF shows most of the possible thunderstorms will be in NJ. This also supported by the ECMWF. The NAM-NEST is showing areas of high CIN (convective inhibition), so we’ll see if these actually form—

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Thunderstorm Update

Update Sun 7/02 11:05 PM — A quick late update. Tonight’s NAM-NEST and HRRR have some thunderstorms moving through Philadelphia about 1-2 AM. This is a change from earlier models.

Additionally, storms expected Monday afternoon and evening. Another change — Tuesday may also have storms, as the cold front hangs up near here. Updates tomorrow.

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Thunderstorm Update

Updated Sun 07/02 @ 7:42 PM — The TV meteorologists are doing a fine job this evening covering the severe weather outbreak in far western suburbs. Here’s a recent radar with the few severe storms that have developed—

As has been the case both last night and again this afternoon, the models do not have the storms above coalescing into a line that will enter Philadelphia.

On the contrary, the HRRR model runs, supported by the Canadian models, have forecast that these storms will move to our north and to our south this evening, largely missing the immediate Philadelphia area.

The reason for the storms not entering Philadelphia— a strong area of negative vorticity (sinking motion) will be over Philadelphia, dampening out the storms—

We never know in advance if the models are correct about exact placement of severe weather, but that’s the current model forecast. And I imagine that’s why you visit this blog.

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Live Thunderstorm Blog 07-02-23

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Sunday Thunderstorm Outlook

Updated Sun 07/02 @ 9:26 AM — As forecast last night, the heavy showers and thunderstorms last night stayed far northwest of the city, with most areas in the Delaware Valley getting 0-0.02″ of sprinkles.

Last night’s early models had today’s potential storms strangely bypassing the immediate Philadelphia area, but the 06z models now show Philadelphia in the path of some strong storms today.

The latest HRRR and RAP model runs have just become available (12z runs) and show thunderstorms developing in place and moving in between 4:30 PM and 8 PM. Peak is 6-7 PM.

Despite very high “precipitable water” (PWAT ) of over 2 inches, the models are placing heavy rain accumulation north of the city. Here’s the forecast total precipitation, which is low considering the PWAT, suggesting that the storms won’t linger—

Comparing today’s forecast severity parameters to recent severe events, the potential severe storms with damaging winds today is high—

Today’s HRRR Forecast Severity Table—

⇣	Sept 1 , 2021 Tornado Outbreak (example of highly severe)	Recent April 1st 2023 Tornadoes (Example of severe)	Today’s 12z HRRR Forecast	Today’s Impact	Today‘s Notes
CAPE Joules/kg	3500-4200	2100	2500-3204	⚑⚑
Helicity m^2/s^2 (tornados)	1350	655	208 (420)	↔ ⚐	High southern Chester County
Vertical Shear 1/sec	40-46	40-45	18	↓ ↓
Precipitable Water	2.7″	0.83”	2.1″	⚑⚑
Lifted Index º K	minus 6º	minus 9.3º	minus 6.2º	⚐	average
HRRR Hail inches	1.9	1.4	1.6	⚑⚑
Thunderstorm Echo Tops	46,000 ft	32,000 ft	45,000 ft	⚑⚑	very high
Peak Wind Gusts mph	40-50	40-50	55	⚑⚑
Storm Motion Shear Vector Alignment	Aligned – ~ 90º	Almost aligned	aligned-curved direction	⚑
250 mb Jet Stream Wind mph	63	135	46	↓

Sunday Update

Updated Sat 7/01 10:40 PM — With the backdrop of having had a cluster of storms move through Cape May County this morning, unpredicted by any model, I’m going to attempt to forecast the showers and storms expected on Sunday.

A warm front will move through the area tonight into Sunday morning with showers and thunderstorms. Most likely time is from 2 AM to 5 AM. The models are keeping the storms mostly far northwest of the city, although some may make it in here.

Sunday morning will start cloudy, but sunshine should break through high thin clouds by noon.

The warm front hangs near us on Sunday. High moisture and instability will cause more storms to develop late afternoon and evening, with increased chances between 4 PM – 10 PM. Strangely, tonight’s models have most of the activity moving northwest and south of the city, somewhat missing the immediate Philadelphia area.

It’s always difficult to know if the model placement of the storms will be accurate.

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Updated Sat 07/01 @ 9:25 AM — According to models, the clouds over us this morning should dissipate by noon. The slowly approaching warm front seems to be moving a bit faster than forecast yesterday. Some thunderstorm activity expected moving into Philadelphia as early as 8 PM this evening (HRDPS) but the latest HRRR keeps it moving in until after midnight.

This morning’s water vapor image with superimposed RAP model jet stream level wind streamlines. I’ve drawn the warm front in —

Some “interesting” weather expected Sunday.

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Updated Fri 6/30 @9:41 PM — I’ve revised the Sunday forecast below

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Previously Posted Fri 8:19 PM —

A stationary boundary running generally west-east to our south will move north as a warm front Saturday night into Sunday morning. The exact timing varies from model to model, but somewhere between daybreak and noon on Sunday is the general trend, although some models have it hanging up in our area. —

Before the warm front, showers develop, but all the models keep the showers and thunderstorms from moving eastward during the daytime on Saturday . Western Chester county and areas west may see some showers and thunderstorms Saturday evening.

A cold front comes through later Monday with showers and thunderstorms.

Tuesday, the 4th of July, looks very nice.

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