Category Archives: Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Thursday Forecast Update

Posted Thursday 12/05/24 @ 8:44 AM — There are showers/snow showers to our west that will likely move just north and just south of Philadelphia this morning, perhaps grazing us.

Current Radar with superimposed MRSMS radar, Omega (vertical motion -yellow contours) and wind streamlines (green) at 10,000 feet. Arrows show likely path of the main showers, but additional showers/snow showers may break out dynamically. (Click on image for a larger view.)

As for the winds, they will be here, as forecast by mid to late morning. Latest RTMA (real time mesoscale analysis) at 8:15 AM shows the higher wind gusts are moving towards us from central PA

Current wind gust onditions based on the RTMA This area of high winds will be here shortly. (Click on image for a larger view.)

Quick Update

Posted Wednesday 12/04/24 @ 11:30 PM — With the critical upper air temperatures all below freezing, I think the models are showing too much rain and not enough wet snow here. While little or no accumulation is still expected, more of the squall showers will have wet snow flakes instead of rain drops, even near the city.

Tonight’s GFS shows critical level temperatures all below freezing here. Only near ground temperatures are in the upper 30s

Thursday Forecast Update

Posted Wednesday 12/04/24 @ 7:30 PM — There has been little change in the forecast for Thursday. Some rain showers this evening will move out later.

The strong cold front moves through Philadelphia about 6 AM accompanied by light scattered rain showers with some scattered snow showers/squalls to our northwest. Wind gusts near 40 mph will increase to near 50 mph towards noon.

12-04-24 18z GFS forecast for 7 AM Thursday. Green = rain Violet = snow. showers The purple line is the 32º isotherm at 900 mb (about 3000 feet) Near ground temperatures will be well above freezing. (Click on image for a larger view.)

Temperatures drop in the afternoon to below 32º by late afternoon.


Wednesday into Thursday: Active Weather

Posted Tuesday 12/03/24 @ 4:32 PM — An approaching warm front on Wednesday will bring windy conditions and perhaps some shower activity in parts of the Philadelphia area Wednesday evening.

Cold air is plunging towards us with the cold front expected to move through about 5-7 AM Thursday with showers and increasingly windy conditions.

Tuesday afternoon’s 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. Cold air rushing towards us. (Click on image for a larger view.)

Winds increase significantly after the frontal passage as temperatures drop. Additional rain showers and even some snow squalls possible with gusty winds in the 40-50 mph range Thursday late morning through much of the afternoon.

Total precipitation should be very light, in the range of 0.05″ rain or snow water equivalent.

Cold and unsettled for Friday.


Strong Cold Front Thursday Morning

Posted Tuesday 12/03/24 @ 10:24 AM —Windy conditions and periods of sun and clouds expected for Wednesday. Increasingly cloudy later in the day.

An arctic cold front will move through Thursday morning. The big feature will be the high wind gusts, over 40 mph and the rapid drop in temperatures behind the front. Snow squalls (minimal to no accumulation) may occur a few hours after the frontal passage.

Latest RRFS forecast for 7 AM Thursday morning. Some showers, possibly with some snow flakes and wind gusts (contours) with this frontal passage. Higher winds develop later in the morning with possible snow squall.

The front appears to come through with two punches. The actual front (wind shift/pressure change) occurs about 5 AM to 7 AM. Rain showers, possibly with some snow flakes, accompanies the actual front along with gusty winds.

Another gust front develops and moves through later in the morning, around 11 AM. High wind gusts near 45 mph and some snow showers possible. Again, little to no accumulation

Rapidly declining temperatures during the afternoon, reaching below freezing by 3-4 PM.

The weekend looks cold.


Originally Posted Sun 4:36 PM —For several days, the radio and TV forecasters are talking about “SNOW” for late Wednesday into Thursday. My personal feeling is that after months of sunny skies and no rain, they’re starved for attention. As of this afternoon, I don’t see any snow in any of the models deserving this sort of advance mention. (The word “HYPE” does comes to mind.)

Since last Friday, the models have been hinting at the possibility of very light snow flurries or snow flakes mixed with rain late Wednesday evening into into the predawn hours of Thursday. No accumulating snow.

The truth is, the reinforcing cold front responsible for this “snow” is moisture deficient and over the past several days, the models have shown no tendency for any surface low pressure formation. All models show temperatures above 32º here Wednesday night into Thursday and even above the critical snow temperature of 36.5º

Only one model, the German ICON-EPS (ensemble model), shows any accumulation and that amount is less than 0.10 inches of snow (a coating at most). Even the ICON-EPS has temperatures above freezing here—

12z ICON EPS accumulated snow at 1 AM Thursday. (Click on image for a larger view.)

We may see some snow showers, lake effect snow that moves from the northwestern PA into our area early Friday morning. Again not worth talking about “SNOW!” in advance for this sort of weather event.

Check back for updates tomorrow


THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Thanksgiving Day Forecast Update

Posted Thursday 11/28/24 @ 1:42 PM — The rain has tapered off on schedule, about 1 PM. Most of the area received the rainfall predicted, about 0.60 – 0.90″ —

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.)

Based on the models, a considerable amount of cloudiness is still forecast for this afternoon, although the latest satellite image shows building high pressure and breaks in the overcast to our west—

Satellite image 1:41 PM with superimposed HRRR pressure gradient. Negative pressure gradient shows the low pressure system will intensify and move to near Cape Cod during the afternoon. Some breaks in the overcast to our far west may move in earlier than forecast by the models, but never second guess the models. (Click on image for a larger view.)

Colder weather tonight and into the weekend. The latest RRFS (experimental) shows light scattered rain and snow showers Friday mid- afternoon —

Todays’ 12z Experimental RRFS foreasts some scattered light showers and patchy dark low clouds Friday afternoon due to instability. Violet shading shows snow precipitation type. (Click on image for a larger view.)

Note: the RRFS is still experimental but under active development and is increasingly used here for forecasts.


Thanksgiving Day Forecast Update

Posted Wednesday 11/27/24 @ 4:56 PM — The models have come together with the Thanksgiving Day forecast. Rain moves in between 1-3 AM and becomes moderate to heavy during the morning hours. The low pressure system exits and intensifies near NYC .

Rain is expected to taper off and end between 1 and 2 PM. It will still remain quite cloudy. Quite windy conditions develop about noon and continue into the afternoon with gusts 35-40 mph.

11-27-24 18z GFS forecast at noon Thursday. Center of low is over Long Island Sound and drier air shuts off the rain in our area by 1-2 PM (Click on image for a larger view.)

It will get cold Thursday night and colder into the weekend.

Friday starts sunny but instability cloudiness develops late morning and widely scattered rain showers are possible during Friday afternoon, especially northwest of the city. Far northwestern areas may see some snow showers.


Thanksgiving Day Forecast Update

Posted Wednesday 11/27/24 @ 8:27 AM — Last night’s models show a faster moving storm and somewhat lower rainfall amounts for our area.

Most models show about 0.60″ of rainfall, starting about 2 AM Thursday morning and ending about 1-3 PM Thursday. (The GFS continues with about 0.8″)

Here’s the latest RRFS (experimental) model forecast for 2 PM showing the departing rain—

11-27-24 06z RRFS experimental model forecast for 2 PM showing simulated radar/rainfall at 2 PM.(Click on image for a larger view.)

The weather pattern gets cold starting this weekend.


Posted Tuesday 11/26/24 @ 4:44 PM — The cold front moved through this morning and parts of our area had a ‘reasonable’ rainfall, while others did not.

Here’s the MRMS precipitation summary for this morning’s 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.)

No significant change in the forecasts from my earlier updates for Wednesday through Friday.

Wednesday starts sunny but will have increasing clouds during the day. By 3-4 PM, it should be mostly cloudy.

Rain starts after midnight or closer to 2 AM Thursday morning. Moderate rain, heavier in the late morning, tapers off during the afternoon and may end as early as 3-4 PM, although the latest NBM has lingering sprinkles through 6 PM or so. Clouds linger into the evening. Windy and gusty!

The models are cranking out a generalized 0.65″ to 0.90″ with the usual scattering of lighter and heavier amounts.

Friday marks the beginning of a colder, mostly sunny and dry pattern that lingers through at least next week. Dry-passage cold fronts will bring high temperatures down quite a bit next week.


Tuesday and Thursday Forecast Updates

Posted Monday 11/25/24 @ 4:57 PM — Little change with the forecast for Tuesday and increasing clarification of the rain forecast for Thursday with a faster exiting storm .

A cold front moves through during the morning Tuesday. Showers will give us about 0.15″ to 0.20″ with the greater rainfall (as usual) falling north and west of the city. Skies clear and sun is expected by the early afternoon. Colder weather moves in for Tuesday night and Wednesday.

Wednesday will have clouds from the city westward in the morning, then increasing clouds west to east throughout our area.

Rain begins a few hours after midnight Wednesday and continues Thursday, Thanksgiving Day. It may be windy and gusty as low pressure intensifies off the NJ coast. Rainfall is consistently forecast to be in the 0.60″-0.80″ range.

For travelers on Thanksgiving, unfortunately it looks fairly rainy and somewhat windy.

Rain may end about 2-3 PM around Philadelphia and towards evening in NJ according to the latest GFS and ECMWF models which is a quicker exit than previously forecast.

Latest GFS with the rain exiting about 3 PM Thursday—

11-25-24 18z GFS forecast for 3 PM. Rain quickly exiting our area. (Click on image for a larger view.)

Dry, windy and colder Friday with periods of instability low level cloudiness


Thanksgiving Weather

Originally Posted Sun @ 8:55 PM — —This week’s active weather pattern will be highlighted by a cold front that moves through Tuesday morning with some showers, followed by colder temperatures. Another highlight will be a storm that approaches Wednesday night into Thursday morning bringing rain to our area.

The models are in good agreement with the cold front passage Tuesday morning. Most are cranking out 0.25 inches of much needed rain with this front. Colder temperatures are expected Tuesday night into Wednesday.

A storm approaches late Wednesday night into Thursday. There’s been considerable uncertainty about both the track of this storm and its intensity. Much has to do with the size and configuration of the mass of cold air that descends down following the cold front on Tuesday.

The AI models have had a faster, more southern track with little intensification of this storm and very little rain for us. The latest GFS is somewhat similar.

However most of the models have moved towards a track that is further north with greater intensification and brings about 0.75 inches of rain for our area.

The latest ECMWF is most aggressive with this system —

11-24-24 12z ECMWF forecast for Thursday morning. This is very aggressive with the intensification and the northward track, but is not necessarily correct. (Click on image for a larger view.)

Since there’s so much spread in the models, I expect there will be further changes in the forecast for Thanksgiving Day. Stay tuned.