All posts by GFS

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Friday & Weekend Outlook

Posted Friday 03/28/25 @ 8:38 AM — Over the past several days, there have been significant changes in the model forecasts for this weekend. Here’s a brief summary—

  • The warm front will become stationary far north of our area. This area will be the focus of most of the rain for this weekend. Much of the rain will stay to our north. What had looked to be a wet latter half of Sunday, now appears to be much dryer.
  • Rain from the system will affect our area on Monday and Monday evening instead of Sunday evening into Monday.

Current water vapor image—

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. The red line north of the red warm front will be the area that receives the most rain with this system. (Click on image for a larger view.)

As for today, Friday, most models still have the showers associated with the advancing warm front to pass us to the northwest. The ECMWF-AI, the HRRR and the NAM-NEST keep a forecast of very light showers Friday evening, anytime between 6 PM and midnight.

I’ll post my regular “Weekend Weather Forecast” late this afternoon with an update.

Thursday and Friday Outlook

Posted Thursday 03/27/25 @ 10:04 AM — I’m finally hearing the words “near 80 degrees” for Saturday in the TV/Radio forecasts. The ECMWF-AI model has been predicting these temperatures since Tuesday.

For today, Thursday, it will be sunny and continued windy and somewhat chilly.

To get to 80 degrees, a warm front will need to pass through our area Friday night.

ECMWF-AI-Single forecast for 2 PM Friday.

Earlier this week, the models only showed showers to our far northwest with this warm frontal passage. The latest models are showing some showers breaking out as early as Friday afternoon ahead of the front.

Here’s the latest HRRR which is forecasting showers and thunderstorms as early as 4 PM Friday afternoon—

Latest HRRR (12z) forecast for 6 PM Friday evening. (Click on image for a larger view.)
Thursday and Weekend Outlook

Posted Wednesday 03/26/25 @ 5:15 PM — Showers formed, mostly to the north of the Philadelphia area today, and radar showed precipitaton over Philadelphia which evaporated before making to the ground. Significant shower activity broke out at the Jersey Shore this afternoon from the upper air disturbances discussed in this morning’s update.

Thursday is still showing cooler temperatures,(53º-55º) but plenty of sunshine. Still somewhat windy and gusty.

A warm front moves through Friday night and the ECMWF-AI-Single and Canadian RGEM models are still showing 80º+ for our area on Saturday.

ECMWF-AI forecast for Saturday at 2 PM. The Canadian RGEM shows even higher temps, although it tends to run warm. (Click on image for a larger view.)

Rainy weather moves in late Sunday afternoon and continues through Monday. the Phillies opener may be affected.

ECMWF-AI Forecast for Sunday at 2 PM. (Click on image for a larger view.)
Wednesday Forecast Update

Posted Wednesday 03/26/25 @ 9:48 AM — Several models (ECMWF, Canadian RGEM, German ICON) are showing some fast moving instability showers moving through here early afternoon. There will be some sunshine in the [late] afternoon, according to the HRRR, but not as much as forecast yesterday. So clouds and some sprinkles is a better bet for late morning and early afternoon.

Current Water Vapor shows showers likely to pass to our north, but positive upward motion just to our west may produce showers here between noon and 1 PM and in NJ—

Current Water Vapor with RADAR and RAP Model low level Omega (upward motion) X denotes centers of upward motion leading to potential showers. (Click on image for a larger view.)
Wednesday through Saturday

Posted Tuesday 03/25/25 @ 6:04 PM — The fast moving low pressure system expected to form this evening will remain to our south. Rain may extend north into South Jersey, but the Philadelphia area will remain dry. Colder weather for Wednesday and Thursday with high temperatures around 50º with sunny skies. A warm up Friday. A big surprise for Saturday- high temperatures may approach 80º!

ECMWF-AI Temperature forecast for 2 PM Saturday! Contours are in 1º increments. (Click on image for a larger view.)

A rainy period develops Sunday into next Monday.

Winds Return for Tuesday

Posted Monday 03/24/25 @ 5:50 PM — Windy conditions, especially Tuesday morning, with gusts 25-30 mph. Highs return to about 57º-58º after a cold morning. Some clouds move in late afternoon.

Mon 5:47 PM —Forecast Review — The rain ended about 4 PM and some sun is breaking out as I write this. Total rainfall, was somewhat higher than forecast in areas east of the city.
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)   It appears that there are some radar artifacts in this MRMS summary.    (Click on image for a larger view.)

Posted Monday 03/24/25 @ 8:58 AM — Based on radar and the latest HRRR, the rain will be ending about 2 PM-3 PM around Philadelphia and about 5 PM to 6 PM at the Jersey Shore. (The Canadian RGEM has the rain ending about 3-4 PM here with some sun possibly by 6 PM. )

Radar at 8:50 AM with superimposed RAP mode low level Omega (vertical velocity pressure). Some enhancement of the rain this morning around Philadelphia is expected with positive Omega. The entire line is moving to the east with the storms moving to the northeast. (Click on image for a larger view.)

As for that potential ‘experiment’ with the ECMWF-AI model, its forecast for some rain here is now late Tuesday night, with light rain ending for the daytime Wednesday. The GFS has moved closer to the ECMWF-AI with some rain in NJ late Tuesday night.

Originally Posted Sun @ 4:25 PM — —Low pressure and an associated cold front will move through on Monday. Rainfall looks to be in the 0.45″ range, but several models have as much as 0.75″ of rain falling over our area. Rain starts before daybreak Monday and continues through at least 4 PM, when any remaining precipitation will become light and widely scattered.

Overall, this coming week looks to be colder than recent weeks with a persistent dip in the jet stream over the Central and Northeastern US.

The current satellite water vapor image with superimposed RAP model parameters and MRMS radar shows the setup that will be persistent—

Current (Sunday afternoon) 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. A persistent dip in the jet (white arrows) will be with us for most of the week. (Click on image for a larger view.)

Of interest is the energy in the Pacific Northwest diving southward into the upper trough. The latest ECMWF-AI model shows another storm developing Wednesday which lends itself to another “AI model Experiment“.

Basically this AI model shows much more development of this Wednesday low pressure system than the either the GFS or ECMWF—

Wednesday forecast from the latest ECMWF-AI-Single model. Much greater storm development than either the GFS or ECMWF (Click on image for a larger view.)

Yet another system associated with a warm front approaches Friday or Saturday. Temperatures look to moderate by next weekend.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx

Update 03/23/25 @ 8:42 AM — Sunny skies this morning will begin to very slowly fade as high cirrus clouds move in about noon. It likely won’t be truly ‘cloudy’ until after 5 PM.

Rain moves in before daybreak Monday and continues through about 4 PM, with some widely scattered showers afterwards. Total rainfall ranges from 0.32″ to 0.70″ in the models. Here’s the ECMWF-AI-Single total rainfall forecast—

06z ECMWF-AI Single Total rainfall for Monday Contours are 0.1″ (Click on image for a larger view.)

Update Sat 3/22 7:38 AM — The higher resolution models have any light showers moving through between 4:30 PM and 7 PM this evening. The lower resolution models keep any showers to our north. That includes the AI models.

Originally Posted Fri 5:01 PM —A reinforcing cold front will pass through about 2-5 PM Saturday afternoon. There will be a chance of light, scattered sprinkles/showers during the mid to later afternoon after the cold front passage.

NBM forecast hourly precipitation at 6 PM Saturday (Click on image for a larger view.)

Another approaching system for Monday will bring some cloudiness late Sunday with rain likely Monday.

Saturday Forecast

Cloudy early, then a varying degree of cloudiness with some sun through much of the afternoon. The front comes through mid to late afternoon with light sprinkles/showers. Increasingly windy and gusty in the afternoon. Temperatures drop below freezing Saturday night into Sunday morning.

NBM high temperatures: Blue Bell, PA 60º Philadelphia, PA 62º
Above average uncertainty (based on standard deviation): ±2.2º

Sunday Forecast

Sunny and cold in the morning, then sunshine through slowly thickening high clouds in the afternoon. Windy in the morning, diminishing during the afternoon.

NBM high temperatures: Blue Bell, PA 49º Philadelphia, PA 51º
Low Uncertainty (based on standard deviation): ± 1.7º