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Sun 6:48 PM —Forecast Review — The REFS high temperature forecast was way too warm today. The official high was 84° in Philadelphia. I suspected that might be the case. The REFS isn’t ready for prime time.

Posted Sat, 06/01/24 @ 7:19 PM— It appears that temperatures may be a little higher on Sunday than forecast yesterday. For a change of pace, I’m going to post the experimental REFS instead of my usual NBM model. The REFS is forecasting in the upper range of the NBM model’s temperature spread, but the NBM often runs a bit too cool.

Today’s 12z REFS model forecast temperatures at 3 PM. (Click on image for larger view.)

The experimental REFS is the ensemble version of the experimental RRFS. Being an ensemble, it consists of the mean (average) and statistical spread (standard deviation) of a group of models or variations of models. In the REFS case, the group of models consists of time-lagged versions of the RRFS and HRRR and perturbations of these same models.

There’s still a fair amount of clouds and sunshine through clouds forecast for Sunday, so we’ll see if these high temps are forecast too high.

Previously Posted Fri 3:30 PM —High pressure will gradually move off the coast Saturday through Sunday. A system to our west will be slow to move in, keeping our area dry over the weekend.

Much of next week looks somewhat unsettled.

NAEFS forecast for 2 PM Saturday. High pressure off the coast will keep fair skies for Saturday. The system in the Midwest will bring some high clouds for Sunday. (Click on image for larger view.)


Sunny and pleasant. High 81-83º (average uncertainty)


Sunshine through a thickening layer of high cirrus clouds. Light scattered showers will likely wait until evening or night time. High 83-85º (higher than average uncertainty due to cloud cover)


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Rain-Free through Sunday

Posted Friday 05/31/24 @ 9:13 AM — The latest model runs have backed off on the light showers that had been expected to move in during the day on Sunday. It now appears that we’ll have gradually increasing clouds and any light showers, if any, won’t move in until early Sunday evening.

The latest ECMWF , which had been quite aggressive with the rainfall Sunday evening, has joined the latest GFS with little in the way of rainfall—

ECMWF 00z Sunday 8 PM forecast
Latest ECMWF (06z) 8 PM Sunday forecast

So a very nice weekend overall.

Saturday we’ll get into the low 80s (81-83º) and Sunday (82-84º) Due to the cloud cover, there’s a bit more uncertainty regarding high temps on Sunday.

Delightful through Saturday

Posted Thursday 05/30/24 @ 9:42 AM —The cold front moved through last night and unseasonably cool delightful weather will be with us through Saturday.

Current water vapor imagery shows the air mass over our area and the disturbances setting up to move in sometime Sunday—

Water Vapor image with superimposed RAP 500-1000mb thickness (yellow), jet stream winds and potential vorticity (violet)(Click on image for larger view.)

The big question is the timing of the next system on Sunday. Current trends are for it to be cloudy with light showers possible in Philadelphia Sunday afternoon. The light showers may arrive at the shore later in the evening.

Gusty Showers/Thunderstorms Wed Evening

Posted Wednesday 05/29/24 @ 8:39 AM — A cold front associated with an upper and surface trough will move through this evening.

The models have come together with a time frame of 6-8 PM, earlier southwest Chester county, for showers and embedded thunderstorms to move through. Some locations will receive an inch of rain, while adjacent areas less than a quarter of an inch. So the heavier rain will be spotty and localized. The heaviest rain is expected northern Bucks county and north of Allentown, as well as north central NJ.

The experimental RRFS model didn’t do bad for last Sunday’s rainfall. Here’s the RRFS total rainfall forecast for this evening—

Today’s 06z RRFS model (experimental) total rainfall forecast for Wednesday evening (Click on image for a larger view.)

As mentioned yesterday, the storms will move in from the southwest with gusty winds, which appears to be the main potential hazard. Truly severe weather not expected.

Skies clear by daybreak Thursday.

The weekend had been looking fine, but the latest NAEFS shows a warm front with showers moving in on Sunday—

Showers later Wednesday Afternoon

Posted Tuesday 05/28/24 @ 7:44 PM — A surface and upper trough approaches Wednesday with an increase in clouds after noontime with with showers and maybe some thunder during the afternoon.

Western suburbs may see some showers as early as 1-2 PM, but many models hold off the showers until 4-6 PM closer to the city. Some models are showing gusty winds preceding the showers late afternoon.

This afternoon’s GFS forecast for 2 PM Wednesday shows an upper and surface trough moving through. The GFS shows an earlier start to the showers just west of the city. (Click on image for a larger view.)

Total rainfall looks to be light. Showers continue into early Thursday morning with rapid clearing by about 10 AM. Becoming windy.

Cooler and windy for Thursday afternoon.

Previously Posted Tue 12:20 PM —Sunday’s rains were not all that heavy or severe. Here’s the MRMS-based rainfall summary —

MRMS combined rain gauge & radar-based measurement of rainfall received. Color shading is in inches. Line contour numbers are in mm (25.4 mm= 1 inch) Most areas received under 1 inch of rain. (Click on image for a larger view.)

Following a system that may bring us some rain later Wednesday, a large, cool high pressure system will bring very nice weather possibly through the weekend—

NAEFS forecast for Thursday at 11 AM. Large high pressure will move down over our area providing cool, dry weather likely through the weekend. (Click on image for larger view.)

Next week should see a return to much warmer temperatures.