Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Friday & Weekend Outlook

Update Fri 5/23 8:51 AM — The latest RRFS model runs keep most of the day dry with clouds and breaks of sun. Scattered showers become more numerous after 5 PM into the early evening.

Posted Thursday 05/22/25 @ 5:43 PM — Rain continues to rotate around the main area of low pressure. This system will eventually move off to the northeast over the next 48 hours.

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. Low pressure moves off to the northeast over the next 48 hours. (Click on image for a larger view.)

Friday: Relatively cold air aloft will move in behind the system during the first two days of the weekend. Looking at the best match for Friday’s forecast, it appears that we may see some sun at times Friday morning. Cold air aloft will cause enough instability for clouds to form with scattered showers in the afternoon, especially mid to late afternoon.

It will be windy and gusty. Cool! High near 65º

Saturday: Cold air aloft will result in considerable low clouds (stratocumulus) especially by later morning and during much of the afternoon. There’s still a chance of light scattered showers. It will be windy and gusty. High near 65º

Sunday: More sun, but still periods of some cloudiness. Still breezy/windy. High near 67º

Monday: Mostly sunny. High near 68º

Thursday and Friday

Posted Wednesday 05/21/25 @ 7:43 PM — A secondary coastal low is expected to form tonight and will bring heavier rain tonight into Thursday.

Today’s 18z GFS forecast for 8 AM Thursday. Secondary low develops off the NJ coast. (Click on image for a larger view.)

A line of heavier rain is moving through Central Pennsylvania this evening and will arrive here later this evening.

Thursday will have periods of rain on and off during the day and into the evening hours.

Friday will still be cloudy, windy and chilly with a chance of showers, especially in the afternoon.

The weekend will feature gradual clearing. Plenty of clouds on Saturday and even Sunday may have some cloudiness develop mid day due to instability. Monday looks to be the best day. It will be chilly and windy much of the weekend; it won’t feel like the beginning of summer.

Wednesday Thursday Forecast

Posted Tuesday 05/20/25 @ 6:02 PM —Rain moves in from the southwest, reaching us between 7 and 9:30 AM on Wednesday.

YES, THE UNIDATA SERVER IS AGAIN UP AND RUNNING. BUT FOR HOW LONG? 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. (Click on image for a larger view.)

(The onset of the rain has moved later with each model run.) Wednesday looks rainy for most of the day, perhaps with some breaks at times. Heaviest rain likely during the afternoon hours.

A possible break in the action Wednesday evening, then more rain, on and off through much of Thursday. Thursday’s rain will likely be more showery and intermittent than Wednesday.

It will be windy and become gusty, especially Wednesday night into Thursday morning.

About 1 inch or more of rain is expected.

Improving conditions on Saturday through Monday. Saturday will be quite cold and windy.

The Trump Administration is withholding National Science Foundation (NSF) funds. The MRMS and live Satellite Water Vapor data I post here is from Unidata, funded by the NSF. The data has become “temporarily unavailable” as of this afternoon, as announced two weeks ago. The support teams for the servers have been furloughed, placed on temporary leave.

So, no more MRMS rain totals and fancy model superimposed water vapor until….

I don’t want to get political here. But what’s going on makes me angry and sad.

Tuesday Update

Posted Monday 05/19/25 @ 8:36 PM — We had much more cloudiness for much of the morning and early afternoon today than forecast by any model. Skies eventually cleared.

For Tuesday, the approaching system has slowed down and it appears that any rain will wait until daybreak Wednesday.

In the mean time, we’ll start sunny Tuesday morning, but we’ll be sandwiched between low clouds to the north and advancing middle level clouds to the southwest. So we’ll go with sunshine in the morning and sun through high cirrus clouds in the afternoon. It wouldn’t take much for the cloud forecast to be off tomorrow.

Today’s 18z GFS shows us sandwiched between low clouds and mid level clouds Tuesday afternoon. It wouldn’t take much for the cloud forecast to be wrong. (Click on image for a larger view.)

It should be much less windy on Tuesday compared to Monday.

Rain on Wednesday into Thursday. Over an inch is forecast. See this morning’s forecast immediately below for the weekend sneak peak.

This Week & Memorial Day Weekend

Originally Posted Mon 9:42 AM —Currently a low pressure system is gathering strength and moisture near Nebraska and will move eastward—

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. (1) indicated where a secondary low will be spawned. (Click on image for a larger view.)

A secondary low will develop along the eastern Mid-Atlantic from this system. Rain will move in, about 5 AM Wednesday morning and linger in some form at least through Thursday evening and even Friday.

NAEFS model statistical “mode” version with overlaid GEFS model “bias-corrected” precipitation forecast for Wednesday_ (Click on image for a larger view.)

Over an inch of rain is expected with this system.

The big question is the Memorial Day Weekend. The AI model (ECMWF-AI Single) is showing a cut off closed low hanging back, bringing chilly temperatures and the chance of showers even through Saturday.

ECMWF-AI forecast for Saturday afternoon. Closed low off the New England coast with instability showers expected here.

Things look better for Sunday and Monday.

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