Category Archives: Philadelphia Weather Outlook

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Rain Update

Posted Friday 07/12/24 @ 3:40 PM —

So where’s the heavy rain? Not where forecast. So far, the heaviest band set up over eastern NJ—

MRMS rain-gauge measured rainfall combined with rain-gauge calibrated and interpolated radar-based summary of ACTUAL RAINFALL received by 3 PM. Color shading is in inches. Line contour numbers are in mm. (25.4 mm= 1 inch)      (Click on image for a larger view.)

The 2 PM (18z) HRRR still shows areas of heavier rain to fall closer to the city over the next 24 hours, by 2 PM Saturday—

18z HRRR rainfall forecast 2PM Friday through 2 PM Saturday. (Click on image for a larger view.)

We’ll see if it happens!

Posted Friday 07/12/24 @ 11:40 AM —

The latest HREF model (along with the experimental REFS model) are predicting truly unbelievable rainfall totals over the next 24-30 hours. I’m not sure that I buy it. Probably overdone. The latest HRRR shows rainfall totals in the 1.5″=3.5″ range and is likely more accurate.

Here’s the very latest HREF—

Today’s 12z HREF model. The two amounts shown are based on the two different statistical methods that the model uses to combine the data from its constituent models (HRRR, HIRESW, HIRESW-FV3 etc) (Click on image for a larger view.)

Posted Friday 07/12/24 @ 8:58 AM — The first round of showers has moved up over us and it was the first of many rounds of showers and even some thunderstorms that will move through from the southeast for the next 30+ hours.

Radar with RAP model 500 mb wind streams at 8:42 AM. (Click on image for a larger view.)

The models are still forecasting 1-2 inches of rainfall with locally higher amounts through late morning Saturday.

Latest NBM 12z total rainfall. (Click on image for a larger view.)

Clouds may break for sun here in Philadelphia and westward on Saturday, but showers and clouds may linger at the Jersey shore into late afternoon Saturday.

Showers and Thunderstorms move in Friday Morning

Posted Thursday 07/11/24 @ 9:14 PM — The stalled front off of the coast will retrograde westward as a warm front Friday through Saturday.

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). I’ve drawn in the position of the stationary front that will return as a warm front. (Click on image for a larger view.)

High moisture flow will fuel showers and thunderstorms, beginning early Friday morning and lasting into Saturday morning. There’s some indication that considerable clouds and spotty showers may linger into Saturday afternoon, especially east of the city and along the NJ coast.

Rainfall totals will be over 1″ in many areas, with some areas receiving much more.

The latest NBM (00z) total rainfall through 8AM Saturday morning. Additional rain expected after 8AM. (Click on image for a larger view.)

I’ll try to nail down the details with a Friday morning update.

Thu 8:20 AM —Forecast Review —As always, the model precip forecasts gave a feel for range of the rainfall totals, but was far off regarding the placement and axis of the heaviest rain. Accurately captured was the forecast decrease in intensity eastward into New Jersey. Not captured was the heavy band in of rain in Delaware.

Here’s the rainfall totals from last night and compare here —

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

Hot and less humid today. Showers and thunderstorms arrive Friday morning as a stalled front retrogrades westward as a warm front. Showers linger into Saturday morning and Saturday looks to be unsettled with a spotty shower possible through the daytime hours, especially at the shore. Sunday looks to be hot again, perhaps with isolated pop-up thunderstorms

Much Needed Rainfall

Posted Wednesday 07/10/24 @ 4:55 PM — The first period of some much needed rainfall will be this evening, as early as 10 PM in western suburbs and continuing into Philadelphia by midnight. All models have the rain diminishing in intensity as it moves into Philadelphia and then NJ.

This first batch of rain won’t be all that heavy; many areas will receive only 0.10-0.50 inches with a few locally higher amounts in western suburbs.

This afternoon’s HRRR total rainfall this evening. (Click on image for a larger view.)

For Thursday, mostly sunny, through high cirrus clouds. Highs upper 80s just short of 90º

Friday looks unsettled. Clouds and scattered showers moving in from the southeast during the morning. Heavier rainfall at night. Highs in the low to mid 80s.

The rain may linger early Saturday morning, but sunshine by afternoon.

Heavy Rainfall Looking More Certain

Posted Wednesday 07/10/24 @ 8:19 AM — I’m glad I waited the extra 12 hours for forecast clarification. The major models have all moved towards heavier rainfall in the Delaware Valley with the usual significant differences.

Tonight: The initial front moves through about 2 AM Thursday morning with a line of showers and thunderstorms. The front stalls close to the Philadelphia area. The exact location will determine the axis of the heavy rainfall. It appears that the front will linger until Saturday morning with on again, off again showers. Some will be heavy, especially later Friday.

Here’s the latest GFS model—

GFS total rainfall tonight through Saturday morning (Click on image for a larger view.)

Here’s the current ECMWF—

Current ECMWF total rainfall forecast through Saturday morning (Click on image for a larger view.)

So there are unknowns with this forecast: the exact position of the stalled front with the exact axis of heavy rainfall and the exact timing of the heavier bands of rain.

More Humidity and Maybe Some Rain

Posted Tuesday 07/09/24 @ 7:50 PM —

A stalled frontal boundary is expected to be a focal point for some much-needed rainfall late Friday. Unfortunately, there’s a trend with this afternoon’s models for the heaviest rainfall to fall in a narrow band, possibly to our south and east. There’s also some considerable model differences with several showing surface low pressure developing in the southeastern US, while the GFS and ECMWF don’t show this low pressure development.

Too early to say what will happen. I’ll update tomorrow morning with some graphics.

Posted Monday 07/08/24 @ 5:48 PM —The trend for the Tuesday and especially Wednesday is a significant increase in humidity and discomfort, with high temperatures remaining in the 93º-95º range. With the increase in humidity (dew points in the 70s) there will be an increased chance of isolated thunderstorms .

Many areas in our area need rain and the excessive heat is parching lawns and desiccating trees and other flora. Rainfall potential towards the end of the week is increasing and, with the exception of the latest GFS model, the ECMWF, Canadian Global and Germain ICON models are showing rainfall to be exceeding 1 inch in the Delaware Valley by Saturday morning.

The increased potential for rainfall Thursday, Friday and very early Saturday morning is the result of a stalled frontal boundary and a southeasterly moist flow off of the Atlantic. (The moisture from Beryl will likely move past us to our north.) The wettest day, if it plays out, will be Friday—

The latest ECMWF shows rain moving in from the southeast on Friday (Forecast map is for 11 AM) (Click on image for a larger view.)

Previously Posted Sun 6:12 PM —A southwesterly flow of very hot air will remain in place through at least Wednesday. Thursday and Friday, the remains of Beryl with interact with a stalled frontal boundary in our area. The exact situation may be too complex to model in advance, so we’ll have to wait and see.

NAEFS model statistical “mode” version with overlayed GEFS model “bias-corrected” precipitation forecast for Wednesday morning. The remains of Beryl may move to our north over the top of the heat dome (orange 576 contour) (Click on image for a larger view.)

The US Navy’s COAMPS model’s track of Beryl—

Some much needed rain may be in store for Thursday through Friday, but current forecasts aren’t predicting all that much in the Philadelphia area. We’ll have to wait and see the position of the stalled front and the trajectory of the tropical moisture from Beryl.

For tomorrow, Monday, and Tuesday, continued hot, with temperatures in the mid to even upper 90s.

The NAEFS keeps us in the 90s through early next week!

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Friday Forecast

Posted Thursday 07/04/24 @ 7:56 PM — Friday will be similar to Thursday, but somewhat hotter. Highs in the mid 90s and humid. Unlike today, the greatest chance of showers and thunderstorms will be far northwest, north and northeast of us, possibly affecting the north Jersey shore.

Here’s the 7:45 PM MRMS radar, which seems pretty close to this morning’s HRDPS forecast posted below.

MRMS radar with RAP “potential precipitation placement” contours (yellow) (Click on image for a larger view.)
4th of July Forecast

Posted Thursday 07/04/24 @ 12:42 PM —

No significant change in the forecast posted just below, based on this morning’s models.

Posted Thursday 07/04/24 @ 9:28 AM —

A mix of sun and occasional cloudiness for most of today. Cloudiness should be mostly thin, high cirrus cloud type.

Uncertainty remains regarding any thunderstorms – timing and location. The model trend over the past 12 hours has been a slight increase in the chance of widely scattered thunderstorms as early as 2 PM. Most likely location is far west of the city.

The latest ECMWF just available has some heavier showers/thundershower just south of the city during the evening hours. The HRDPS sort of captures the ECMWF and NOAA models with its precip forecast—

HRDPS precip forecast for 7 PM Thursday evening (Click on image for a larger view.)

I’ll do a quick update later this morning

July 4th Weekend – Thursday – Sunday

Posted Wednesday 07/03/24 @ 7:41 PM —

The latest GFS model is similar to the Canadian model and has a few showers and thunderstorms moving into the Philadelphia area Thursday evening. Any showers and storms will be scattered.

Unfortunately, an unsettled pattern develops for Friday and Saturday with a chance of of somewhat more widespread showers and thunderstorms, especially late afternoon and evening, but there’s some possibility throughout period. Otherwise sunshine with periods of cloudiness.

The greatest chance of thunderstorms in the immediate Philadelphia region will be late afternoon Saturday afternoon and evening.

All days appear to be hot with highs in the low 90s!

Dew points in the uncomfortable 70s through Saturday. Dew points drop on Sunday, so it will feel somewhat cooler. Sunday will be dry.

Posted Wednesday 07/03/24 @ 5:46 PM —

The Canadian models just became available after my recent post. They lean more toward some thunderstorm activity later in the evening, even into NJ. I’ve been impressed with the Canadian model’s thunderstorm predictions.

Posted Wednesday 07/03/24 @ 5:21 PM —

The trend for July 4th is hot and steamy with thunderstorms possible western areas. Temperatures will be in the 91-92º range (± 1.4º) for both Philadelphia and Blue Bell locations.

Dew points are forecast to be in the uncomfortable 70s, creating a heat index in the upper 90s—

NBM heat index for July 4th.

It’s still a tough call about potential thunderstorms Thursday late afternoon into evening. They can’t be ruled out, especially west of the city—

Today’s 18z NBM thunderstorm probability at 6 PM. The probability does NOT increase in Philadelphia over the evening hours. While 26% doesn’t sound like much, that is an hourly probability, which is a decent chance. The 15% in Philadelphia is low, but still a possibility. (Click on image for a larger view.)

The HREF gives an indirect probability of thunderstorms through its probability of radar echoes greater than 40 db at 6 PM —

HREF probability of radar echoes greater than 40 db. at 6 PM (Click on image for a larger view.)

So the best we can say for tomorrow right now is that the further east of the city you are, the less chance of showers/thunderstorms in the early evening.

Look for an update tomorrow morning.

Posted Wednesday 07/03/24 @ 8:24 AM —

As updated last night, the latest models are showing an increased chance of thunderstorms moving further into the Philadelphia area than previously thought. Most of the activity should remain west of our area, but there is now a significant probability of some scattered showers and thunderstorms moving in as early as the afternoon and more likely in the evening hours.

06z HREF 1 hour probability of radar echos >40 db. at 9 PM Thursday (Click on image for a larger view.)

Posted Tuesday 07/02/24 @ 9:57 PM —

Tonight’s HRRR shows some showers moving in Thursday afternoon, somewhat negating my earlier outlook. This may change again.

Posted Tuesday 07/02/24 @ 8:46 PM —

Thursday is looking hot again with temperatures at or just above 90º in the city, upper 80s surrounding areas.

There’s been a consistent forecast of showers/thunderstorms that barely make it into Philadelphia during the evening hours. Indeed, most models keep any showers and storms just to our west. This forecast continues to hold with the latest models, so fireworks displays in city and immediate surrounding areas. Western suburbs may see some showers/storms. It’s going to be close, so I’ll continue to monitor it.

Here’s the latest NAM-NEST, showing the eastward extent of the showers/storms at 11 PM Thursday evening—

18z NAM-NEST shows the eastward extent of the showers reached at 11 PM. They seem to hit a wall as they go further east and dissipate. (Click on image for a larger view.)
Monday through July 4th

Originally Posted Mon 8:20 AM —High pressure builds in for Monday and Tuesday with beautiful weather. By Wednesday, the high is offshore and a southerly flow of much warmer (hotter) air moves in late Wednesday—

NAEFS model statistical “mode” version with overlayed GEFS model “bias-corrected” precipitation forecast for Wednesday at 2 PM Notice the orange 576 line, the approximate edge of the heat dome will be pushing back into our area. The next weather maker is the low pressure system entering the Dakotas. The hurricane in the Caribbean ocean isn’t visible on this map. (Click on image for a larger view.)

By Thursday, July 4th, the heat dome has moved up past us and moisture associated with the low to our west is on our doorstep—

By Thursday, July 4th at 8 PM, the GFS has the heat dome edge north of our area and some moisture and showers at our doorstep with a warm front. (Click on image for a larger view.)