#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—

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—

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—

The NAM forecast shows the upper low—

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.

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—

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.

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.

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.)

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.

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 #weather #PAwx

Clearing Today – Cold Friday- Snow Saturday

Posted Thursday 02/13/25 @ 8:47 PM — Accumulating snow on Saturday afternoon looks less likely. Possibly a coating in northwest suburbs before a changeover to rain.

Posted Thursday 02/13/25 @ 9:28 AM — Several large shifts in temperature and weather over the next several days.

Today (Thursday) — Clearing around 2-3 PM and becoming windy and gusty. Mild but temperatures chill down later today and tonight.

Friday (Super Bowl Parade) — Sunny breezy and cold.

Saturday— Snow develops in the morning from west to east. Precip changes to sleet, then rain early evening hours. Preliminary snow accumulation (GFS model) about 1-3 inches mostly from the city north and west.

Wednesday Night through Friday

Posted Wednesday 02/12/25 @ 5:13 PM — Our next in a series of disturbances is approaching and should be here by 6 PM -8 PM—

Temperatures in most of the region will be above freezing, but some of the earliest precip may begin as light snow, quickly changing to rain.

Total rainfall is expected to be about 0.45 to 0.65″ tonight with higher amounts in South Jersey and near the coast.

Thursday: Cloudy in the morning, then sunshine breaks out in the afternoon. Windy and gusty with highs in the low 50s!

Friday: The Super Bowl Parade will have sunshine and breezy conditions. High temperatures will be near 37º in the city.

Rain Wednesday night

Posted Wednesday 02/12/25 @ 9:44 AM — The models maintain cloudiness for us today, Wednesday. Many models crank out some very light snow or flurries beginning in the afternoon. (Temperatures in the upper atmosphere remain cold enough for snow from the city northwestward despite temperatures moving above freezing for much of the area.)

As another area of low pressure slides towards us, temperatures at all levels will rise above freezing. Total additional rainfall about 0.30″-0.40″ water by Thursday 8 AM.

Wed 9:23 AM —Forecast Review —The immediate Philadelphia area received slightly more precipitation in the form of snow than forecast below by the NBM . Areas to the west and north received slightly less than forecast. Areas in NJ received somewhat more than forecast. Overall, the forecast was fairly good.

Here’s the MRMS precipitation estimate for the past 24 hours given in inches of water. Based on actual measurement, multiply by 8-10 to get approximate snow depth.

Measured snow totals from the NWS–

...Bucks County...
Levittown                    3.5 in    0548 AM 02/12   Trained Spotter
2 ESE Newtown                2.5 in    0634 AM 02/12   Other Federal
1 NNW Langhorne              1.8 in    1130 PM 02/11   Trained Spotter
Upper Southampton Twp        1.6 in    1250 AM 02/12   Trained Spotter
Plumstead Twp                1.6 in    0430 AM 02/12   Trained Spotter
Bensalem                     1.5 in    1024 PM 02/11   Public
Fricks                       1.5 in    0709 AM 02/12   Trained Spotter
Furlong                      1.0 in    1230 AM 02/12   Trained Spotter

...Chester County...
East Nantmeal Twp            3.3 in    0700 AM 02/12   Trained Spotter
Berwyn                       3.2 in    1038 PM 02/11   Trained Spotter
West Chester                 3.1 in    0600 AM 02/12   Public
Jennersville                 2.7 in    0556 AM 02/12   Public
1 WNW Chesterbrook           2.7 in    0634 AM 02/12   Trained Spotter
West Caln Twp                2.5 in    0553 AM 02/12   Trained Spotter
East Coventry Twp            2.0 in    0530 AM 02/12   Public

...Delaware County...
Boothwyn                     3.7 in    0120 AM 02/12   Trained Spotter
Chadds Ford Twp              1.8 in    1000 PM 02/11   Trained Spotter

...Montgomery County...
Norristown                   3.1 in    0613 AM 02/12   Trained Spotter
Plymouth Meeting             3.0 in    0100 AM 02/12   Public
King of Prussia              2.7 in    0604 AM 02/12   Trained Spotter
1 E Willow Grove             2.5 in    0600 AM 02/12   Trained Spotter
Eagleville                   2.3 in    1200 AM 02/12   Public
1 NNE Willow Grove           2.0 in    1228 AM 02/12   Public
Eagleville                   2.0 in    0630 AM 02/12   Trained Spotter
New Hanover Twp              1.9 in    0500 AM 02/12   Trained Spotter
East Norriton                1.8 in    1100 PM 02/11   Public
1 ENE Plymouth Twp           1.6 in    1222 AM 02/12   Public


...Philadelphia County...
Philadelphia Intl Airport    3.1 in    0700 AM 02/12   ASOS
1 SSE Center City            3.1 in    0713 AM 02/12   Public
Bustleton                    3.0 in    0523 AM 02/12   Trained Spotter
Fox Chase                    2.9 in    0530 AM 02/12   Trained Spotter

Tuesday Snow Update

Posted Tuesday 02/11/25 @ 7:54 PM — Looking at the latest hourly models (RAP and HRRR), it appears that we may get even less snow than the recent NBM forecast posted. I see very little in the way of pressure falls off the coast and negative omega values are plentiful, meaning less dynamics to result in snow intensification.

The ‘heaviest’ snow (air quotes placed for a reason) is still forecast to occur between 9 PM and midnight, then taper and end around 3 AM.

Here’s the latest HRRR which shows additional snowfall from 6 PM onward—

Posted Tuesday 02/11/25 @ 4:32 PM — Additional models have become available since my last update. Little has changed with total precipitation around the city ranging from 0.18″ to 0.28″ water equivalent. This translates into a similar snow forecast as described earlier.

Currently light precipitation has just begun to fall in our area. As expected, the main area of precipitation is south of our area. Evaluation of vertical upward motion (“Omega”) shows low pressure will develop far off the Delmarva coast in the area designated (L) . In our area, there are little signs of intensification, but area of strong vertical motion in West Virginia now will bring some heavier snow here about 11 PM or so.

Despite somewhat heavier snow forecast from the ECMWF, I’m sticking with the latest model blend (NBM)—

Show More

Tuesday Snow Update

Posted Tuesday 02/11/25 @ 1:08 PM— This morning’s models continue a trend towards somewhat lower snow totals. Here are the trends—

• A somewhat later start of the snow; about 6 PM to 7 PM close to the city.
• Snow ends well before daybreak Wednesday.
• This morning’s GFS still shows some light snow or flurries early to mid afternoon before the main area of snow arrives between 6 PM and 7 PM.

Here is the latest model blend that incorporates the updated precipitation guidance—

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Tuesday Snow Update

Posted Tuesday 02/11/25 @ 8:43 AM — Snow is still in the forecast for later today. Current water vapor and radar shows the main area of precipitation is to our south—

Here are the trends based on last night’s models—

• I’m hearing the words “snow storm” and “3-6 inches” on the radio. Based on consistent model forecasts, I think this event is being hyped by some of the media. (The ECMWF is forecasting the higher totals.)
• Most of our immediate area will receive 1-3″ of snow.
• Snow begins 5 PM-7 PM although the GFS consistently shows an earlier brief period of light snow or flurries about 1-2 PM. Not all models are on-board with this earlier brief period.
• Snow ends before daybreak, but some models continue with light intermittent snow into the morning hours.

Here’s the current NBM snow accumulation forecast—

Light snow develops again late Wednesday afternoon with a rapid changeover to rain.

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Active Weather Pattern- Snow Likely

Posted Monday 02/10/25 @ 6:03 PM — The latest GFS, just available, shows some light snow/flurries early afternoon Tuesday, before the main area of snow moves in between 4-7 PM.

Posted Monday 02/10/25 @ 5:17 PM — A quick update on the expected snow for Tuesday evening. Here are the trends—

• Total accumulations have moved somewhat lower than had been forecast this morning.
• Light snow moves in about 4-7 PM from the southwest.
• Snow tapers to flurries between 8 AM and 10 AM Wednesday.
• Snow re-develops Wednesday evening, but changes to rain. Rain may be heavy.

Here’s the latest model blend snow accumulation forecast—

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Posted Monday 02/10/25 @ 10:06 AM — One more thing… Following a break in the precipitation on Wednesday morning and early afternoon, snow will redevelop Wednesday evening, but change to sleet and rain. Heavy rain expected into Thursday.

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Originally Posted Mon 9:42 AM —As mentioned last Thursday, an air mass boundary stretching across the country will be a focal point of low pressure development this week.

Here’s what it looks like on satellite water vapor imagery this morning—

Here’s what the corresponding ECMWF weather map looks like—

Snow is expected to move in during the afternoon on Tuesday and continue through Tuesday night.

A large gradient of precip will set up, north to south, affecting snow totals. Small variations in the intensity and track of this storm will create large uncertainties in actual snow totals.

It should be noted that the AI version of the ECMWF has very little snow for us with this storm. So there’s high uncertainty with this forecast.

The NBM has been doing well with recent snow/sleet forecasts. Here’s its snow total forecast by Wednesday morning at 8 AM —