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Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Forecast Update- Thursday

Posted Thursday 02/20/25 @ 11:03 AM — The models continue with spotty light flurries or snow showers for today, beginning about 3-4 PM and ending by 8 -10 PM. Total snowfall is expected to be very light with little more than a dusting or coating in most areas. Here’s the latest HRRR—

12z HRRR total snowfall for Thursday by late evening. (Click on image for a larger view.)
Thursday Forecast Update

Posted Wednesday 02/19/25 @ 9:20 PM — As posted late afternoon, any light snow/snow showers/flurries on Thursday will occur in the afternoon into the evening due to an an upper level low. The afternoon models and this evening’s latest HRRR/NBM are showing varying amounts of light accumulation, from a dusting and coating to 1/2″ accumulation.

Here’s tonight’s HRRR—

Tonight’s 00z HRRR snow accumulation forecast by 11 PM Thursday.

Here’s the latest 01z NBM, showing even less—

Right now, I don’t see any additional snow likely in the short range or even next week, which may have two periods of rain.

Thursday Forecast Update

Posted Wednesday 02/19/25 @ 5:12 PM — The storm, forecast days ago for Thursday, completely misses our area. No real surprise, since that trend had been captured by the majority of the models for days.

The NBM, perhaps influenced by the NAM forecast, kept snow in the forecast for Southern NJ longer than it should have. (Regardless of when the NAM is retired, the next version of the NBM scheduled for release in April 2025 will be excluding NAM model precip data.)

Thursday will still be cloudy due to an upper air low that passes over our area. A few flurries are possible. Still cold with a high temperature in Philadelphia about 30º-31º and about 2º colder in Blue Bell.

Yet Another Forecast Change

Posted Wednesday 02/19/25 @ 9:38 AM — Last night’s 01z, 07z and the latest 13z NBM model forecasts show a constant evolution towards the southern storm entirely missing us .

Any snow in the immediate Philadelphia area (and parts of South Jersey) being the result of an upper air low. The light snow/flurries/snow showers will occur late in the afternoon Thursday. Here’s the latest NBM—

Today’s 13z NBM forecast snow accumulation by 11 PM Thursday evening. (while I’ve labeled the 0.5″ inch line, there will be no accumulation over the ocean.) :-)(Click on image for a larger view.)

The NAM forecast shows the upper low—

This morning;s NAM forecast for 1 PM Friday showing the upper level low to move east over us. The NAM cranks out 0.5 inches of snow, but it remains an outlier. (Click on image for a larger view.)
Thursday Forecast Update

Posted Tuesday 02/18/25 @ 6:06 PM — The afternoon NAM has backed off from its morning forecast. The model blend (NBM) captures the general trend, with just a coating in the immediate PHL area and 1-3 inches in NJ.

02-18-25 19z NBM snow accumulation by Thursday evening. (Click on image for a larger view.)

I’m keeping an eye on the models and look for an update either this evening or Wednesday morning.

A Change in the Forecast?

Posted Tuesday 02/18/25 @ 9:15 AM — Last night’s models continue forecasting Thursday’s main surface low tracking off to our south and east missing us. The models have been on-again off-again with showing some light snow showers from the upper low that will pass over PA on Thursday.

Of some interest is the latest NAM forecast. (FYI, development of the NAM was discontinued in 2017 and is scheduled for “retirement” in 2025. The NAM has a history of over-forecasting snow in the 48-60 hour time range.)

That said, it is the only model showing the precipitation shield covering South Jersey on Thursday, with some significant accumulation. It’s currently an outlier with this storm. Here’s the current NAM forecast for Thursday—

02-18-25 06z NAM forecast for Thursday. An outlier with this storm, it’s forecasting some significant snow for South Jersey and a coating or so for us. The upper level low shown near Pittsburgh may bring some snow showers here; just a coating in Philadelphia. (Click on image for a larger view.)

With most models at most showing snow showers for Philadelphia on Thursday, I’ve posted the NAM as food for thought. I’ll update later if the other models join in on its forecast.

A note for those of you who are visiting this site from “X“.
Due to the highly unbalanced political environment on X, I’ve considerably cut back auto-posting there. To receive all forecast postings, I recommend following me on mastodon.social or bluesky.social

Dry and Cold

Posted Monday 02/17/25 @ 5:08 PM — Cold high pressure continues to build in. Tuesday and Wednesday will be quite cold and it appears that there may be some cloudiness mid day on Tuesday due to an upper air disturbance.

02-17-25 18z NBM forecast high temperatures for Tuesday. Standard deviation is ± 1.4º (Click on image for a larger view.)

Winds will be subsiding compared to Monday, but wind chills during period of maximum temperatures (3-4 PM) will be in the 11º -17º range.

Those looking for a snow day will be disappointed on Thursday. ALL models are forecasting the over-advertised storm on Thursday to track too far to our south and east. We may see some flurries and the NJ shore may see some light snow.

Originally Posted Mon 9:47 AM —The intense pressure gradient between the low pressure system that departed Sunday and building high pressure continues to create wind gusts in excess of 35 mph. (Gee, I hope no one on TV uses the expression “wind tunnel effect” to incorrectly explain the cause of these winds.)

GFS forecast wind and wind gust meteogram for grid point Blue Bell, PA (Click on image for a larger view.)

For today, a brief period of cloudiness may develop early afternoon due to instability and an upper air disturbance. Otherwise sunny.

Cold high pressure will be with us through at least Thursday. Low pressure that was advertised as bringing us snow Thursday increasingly appears to move too far off to our south.

ECMWF forecast for Thursday- coastal low pressure moves off to our southeast. An upper low (blue L) may bring some light snow showers to us. (Click on image for a larger view.)

It wasn’t too long ago that forecasters would keep an uncertain view of this forecast. A big change has been the development of AI models. With both the GFS GraphCast AI and the ECMWF AIFS models showing this storm moving far southeast of our area, it seems increasingly unlikely that a shift closer to the coast will occur.

Coastal South Jersey may be brushed with some snow on Thursday from this system. And the Philadelphia area may see some snow showers from an upper low pressure system moving over PA. But a significant snowstorm seems very unlikely at this point.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx

Posted Sunday 02/16/25 @ 8:56 PM —The well-advertised storm expected for Wednesday into Thursday looks to only brush the Philadelphia area with possibly 1-2 inches of snow. Areas near the Jersey shore may see substantial snow, based on the current track. Updates tomorrow!

Sun 8:46 PM —Forecast Review — We had the rain and we have the winds! Here’s the MRMS total rainfall (and snow-water equivalent) over the past 48 hours—
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.)

The RTMA is a real-time data model run every 15 minutes, reporting for the previous 15 minutes. Here’s the wind gusts it’s showing at 8:15 PM—

RTMA showing winds and wind gusts at 8:15 PM tonight. (Click on image for a larger view.)

Sunday Forecast Update

Posted Sunday 02/16/25 @ 2:35 PM — Based on the latest radar, satellite and HRRR hourly data, it doesn’t appear that we’ll see those near 60º temperatures forecast by the models yesterday. (Some areas in South Jersey may see those highs about 3-4 PM)

The cold front is in central PA at this time. Some additional showers may accompany the actual frontal passage around 3:30 PM-5 PM.

Latest HRRR 3 hour pressure change (green contours) with superimposed radar and visible satellite image. Some of the precip in Pittsburgh may be snow showers. (Click on image for a larger view.)
Sunday Forecast Update

Posted Sunday 02/16/25 @ 9:23 AM — The latest NBM and HRRR show the heaviest rain to occur here between 12 PM and 3 PM. Here’s the latest HRRR—

Today’s 12z HRRR forecast for 1 PM today. Actual cold front still in central PA at that time. The front is expected to move through here with plunging temperatures and high winds 4-5 PM

Total additional rainfall about 0.45- 0.65″ Wind gusts as high as 40-50 mph between 3 PM and 6 PM and continuing gusty. Rain tapers off and ends about 5- 6 PM or so.

I’m keeping an eye on the potential storm late Wednesday into Thursday. It still appears to have a track too far south for heavy snow here, according the the AI models. Still much uncertainty.

A note for those of you who are visiting this site from “X“.
Due to the highly unbalanced political environment on X, I’ve considerably cut back auto-posting there. To receive all forecast postings, I recommend following me on mastodon.social or bluesky.social

Forecast Update

Posted Saturday 02/15/25 @ 9:32 PM — Tonight’s models show some changes in the Sunday forecast—

  • Total rainfall will be closer to 1 inch or less instead of 1-2 inches.
  • Winds will increase significantly during the afternoon and evening.
  • The most likely time for thunder is about 2-3 PM.
  • The heaviest rain will fall 1 PM to 3 PM.
  • Rain ends by 4:30-6 PM.
Active Weather Pattern

Posted Saturday 02/15/25 @ 5:38 PM — The heaviest rain will be arriving after 9 PM tonight and continue through the night. There may be a break in the rain Sunday morning (8 AM- Noon), following the passage of the warm front. Rain returns by the early afternoon and continues ahead the approaching cold front.

Expect some thunderstorms and very gusty winds in excess of 40 mph. ahead of the cold front on Sunday. The cold front moves through between 4 and 6 PM. Total rainfall for this storm is still expected to be in the 1.5″ range.

Very cold weather returns for next week, as the storm track moves to our south.

A possible significant snow storm for us is forecast for late Wednesday into Thursday.

While the AI models are suggesting much of the snow might miss the Philadelphia area, mostly affecting South Jersey, However the operational models (GFS, ECMWF, Canadian GEM) are forecasting a potential 6+” snowfall for us. Too soon to hang your hat on this forecast.

Here’s the ECMWF for next Thursday—

02-15-25 12z ECMWF forecast for Thursday at 7 AM. (Click on image for a larger view.)
Snow and Rain on the Way

Posted Saturday 02/15/25 @ 10:27 AM —The models, not unexpectedly, are leaning towards less snow/sleet accumulation. The precip is on our doorstep, but a dry lower atmosphere will maintain the 12 PM – 2 PM start time

MRMS and NEXRAD combined radar with RAP model Omega (Click on image for a larger view.)

Here’s the latest NBM snow/sleet accumulation—

Today’s 13z NBM snow accumulation. Most of area will see close to nothing or a coating except northwest suburbs. (Click on image for a larger view.)

Total rainfall for the weekend will be about 1.3″-1.5, although some models have close to 2+” in some areas.

Today’s 13z NBM total rainfall for the entire weekend. (Click on image for a larger view.)
Starting as Snow

Posted Friday 02/14/25 @ 9:39 PM — More models have a forecast of snow accumulation prior to a changeover to rain late afternoon Saturday or Saturday early evening.

The latest HRRR has minimal snow accumulation. The model blend (NBM) is still cranking out accumulating snow, despite temperatures rising above freezing near the surface.

Here’s the latest NBM snow accumulation forecast—

Tonight’s 01z NBM forecast snow accumulation by 6 PM Saturday. (Click on image for a larger view.)

When it comes to snow, long-time readers of this blog know I can’t ignore the NAM. The NAM is forecasting an unreasonably large snow accumulation—

Tonight’s 00z NAM shows an UNLIKELY snow accumulation for Saturday afternoon. Still something to ponder. (Click on image for a larger view.)

Snow moves in about 12 noon to 2 PM, a bit earlier in far western suburbs.

Not mentioned earlier is the considerable rainfall we’ll receive this weekend. Most models are in the 1.3″-1.5″ water range.

Wet and Windy Weekend

Low pressure developing in the central US will move north towards the Great Lakes and will bring rain to our area Saturday, beginning around 12 PM – 2PM as some accumulating wet snow and then transitioning to all rain by 5 PM, if not sooner.

Rain continues Saturday night through much of Sunday, as a secondary low pressure system develops off the NJ coast on Sunday.

WV image Friday at noon showing large system moving towards the Great Lakes with a strong subtropical jet stream adding moisture to the mix. (Click on image for a larger view.)

Saturday Forecast

Cloudy with wet snow or rain mixed with snow developing by 12PM to 2 PM The latest NBM shows some accumulation, but I think it may be over-done a bit. (The latest GFS shows somewhat more snow)—

19z NBM snow accumulation, possibly over-done. I calculate these NBM totals and my algorithm doesn’t include melting and compaction, which is going to be severe here. That said, the latest GFS has about 1.5 inches where I show 0.5 inches. (Click on image for a larger view.)

NBM high temperatures: Blue Bell, PA 38º Philadelphia, PA 41º
High Uncertainty (based on standard deviation): ± 2.4º

Sunday Forecast

Continued cloudy with rain. Quite warm but very windy! Possibly a thunderstorm ahead of a cold front. Temperatures fall following the cold front Sunday late afternoon into the evening.

NBM high temperatures: Blue Bell, PA 61º Philadelphia, PA 58º
Average Uncertainty (based on standard deviation): ± 1.6º