Daily Archives: Sunday, October 19, 2025 5:20 pm

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx #PhillyWx

Friday and the Weekend Outlook

Posted Thursday 10/23/25 @ 6:00 PM — This morning’s high resolution models (12z HRRR, RRFS and NAM-NEST ) all got the cloud cover wrong, but some global models which came out after my update (12z GFS, ICON ) continued to show the cloud cover that did actually develop. Go figure.

There isn’t much happening weather-wise this weekend. The notable exception is the colder temperatures at night. Tonight, many areas just outside the city will see the upper 30s.

18z NBM forecast low temperatures by Friday morning. All temps above are around ± 1.2º (Click on image for a larger view.)

I’m keeping my eye on next week’s potentially stormy weather. Some models continue with the development of a very wet secondary coastal low system; other models show blocking high pressure keeping the rain away from our immediate area. Stay tuned.

Thursday Forecast

Posted Thursday 10/23/25 @ 12:29 PM — Several models seem to have removed the cloudiness forecast for this afternoon that they were all showing yesterday.

Posted Wednesday 10/22/25 @ 5:25 PM — I didn’t focus on any forecast specifics for today (Wednesday), but we had an area of moisture aloft with cold air instability this afternoon resulting in the low level stratocumulus cloudiness that moved in. This will dissipate tonight.

Another area of moisture will rotate into our area from the northwest on Thursday with similar cloudiness developing between 12 and 2 PM, then dissipating around sunset.

Next week is again looking interesting, weather-wise, with a closed upper low inducing coastal low pressure development. There are large differences in timing and specifics, but we may finally get some decent rainfall next week according to the ECMWF-AI and the NAEFS. It looks like any storminess will end in time for Halloween.

Latest ECMWF-AI forecast for Tuesday 2 PM. (Click on image for a larger view.)
Forecast Review

Posted Wednesday 10/22/25 @ 10:01 AM — The rain last night equaled or exceeded the upper limits of the forecast rainfall amounts and the rainfall coverage exceeded most models’ forecasts. The intensification I spoke of did occur, but it was mostly offset by the speed of the precipitation shield. Here’s the MRMS totals for this rainfall—

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)      (Click on image for a larger view.)

Posted Wednesday 10/22/25 @ 10:01 AM — Increasingly seasonably colder weather for the next several days. No rain expected until some time on Monday, The tropical system in the Caribbean increasingly looks like it will move away from the US. The storminess I spoke of for next week is now uncertain.

Wednesday Night- Interesting Weather

Posted Tuesday 10/21/25 @ 7:37 PM — The forecast for cold front expected to move through tonight has been nothing special with only scattered showers and rainfall amounts on the light side (0.0- 0.13″)

I’ve been looking at the current hourly models and I’m seeing things that don’t translate into this simple low rain forecast—

  • Radar echos are indicating somewhat more rainfall occurring to our west than model guidance.
  • Vertical velocity Pressure (Omega) is very significant just to our southwest indicating potential secondary low formation.
  • Three hour pressure tendencies are suggesting secondary low pressure forms near our area.

I’m going to go out on limb and post that there’s the potential for somewhat more rainfall than has been the official forecast. I may be wrong here, but these occasional weather ‘experiments’ are part of my fun of doing these forecasts. As I always say, I guess we’ll see. We could use the rain.

Radar with RAP model vertical velocity pressure (Omega) and 700 mb wind streams. Strong development to our southwest is greater than forecast previously. (Click on image for a larger view.)
22z RAP model forecast Vertical Velocity Pressure at 700 mb. Strong upward motion. Not as much low level moisture as I would expect. (Click on image for a larger view.)

BTW, for weather nerds, the middle and end of next week (just before Halloween) is looking quite interesting and stormy here.

Tuesday

Posted Monday 10/20/25 @ 4:54 PM — Tuesday will be sunny for most of the day and will become mild with highs 69º-70ª. Another strong cold front moves through around midnight into early morning Wednesday. Rainfall with this front will be scattered and on the very light side with accumulations of 0.10″ or less. Windy and gradually colder on Wednesday and colder Thursday.

ECMWF-AI model forecast 2 AM Wednesday. The red and magenta ‘thickness lines’ demarcate very cold average temperatures to this air mass.
Mon 4:17 PM —Forecast Review —Based on the visible satellite loop (and looking out the window), we had much more instability cloudiness this afternoon than forecast. Even today’s 8 AM model runs (12z) of the HRRR and RRFS failed to show the extent of cloud cover this afternoon. Only later model runs of these hourly models captured the widespread cloudiness. The ECMWF-AI model did forecast this cloudiness.
Monday Update

Posted Monday 10/20/25 @ 9:24 AM — The approaching upper trough will cause a period of cloudiness. The showers will miss us. Expect the sun to return from southwest to northeast between 12 PM and 2 PM.

Radar at 9 AM with superimposed RAP model Omega. (Click on image for a larger view.)

BTW, we had between 0.13″ and 0.30″ of rain early this morning. Most areas received at the lower end of this range, at best.

Sunday Evening Update

Posted Sunday 10/19/25 @ 7:45 PM — Current radar is a case-in-point for why I rarely use the word “tracking” regarding weather. Radar shows storms that look to be on a straight “track” to hit Philadelphia.

Current Radar 7:30 PM Sunday with superimposed RAP model low level Omega as dashed yellow contours in red box. (Click on image for a larger view.) (Omega is shown as -ubars/sec not, + ubar/sec where negative values are actually negative of a negative value which is really positive Omega. Confusing, huh? )

But, radar alone doesn’t tell the whole story. A very strong area of Omega (downward vertical motion – yellow dashed contours in red box) is between us and the storms, according the latest hourly RAP model. If the RAP model is correct, this downward motion will reduce the intensity of the line of storms as it moves closer to our area. Hence, the reason for low rainfall totals here.

Monday

Originally Posted Sun 5:20 PM —A sharp cold front moves through after midnight tonight. As has been the case recently, the heavier rain will stay to our far north and west. That said, Philadelphia and its surrounding counties may get anywhere from 0.17″- 0.30″ of much-needed rain. The trend over the past day or so has been towards less rain and the lower range. The story tonight with the front will be gusty winds.

A sharp upper trough moves through about 10AM Monday. Winds and cloudiness (especially from the city northward) will accompany this fast moving trough. Skies clear again in the afternoon. The big story Monday will be the windy conditions with sustained winds just under 15-20mph and gusts over 30 mph.

Another cold front moves through Tuesday night into Wednesday, also with very light showers.

ECMWF-AI forecast for Tuesday at 2 PM Cold front moving through western PA at that time. NOTE the appearance of the RED 540 thickness line. In winter, this indicates temperatures in the mid/upper atmosphere are cold enough to support snow. This is really the first significant dip of cold air this season for us. (Click on image for a larger view.)

Thursday will be quite cold compared to recent weeks.