Category Archives: Philadelphia Area Weather Forecasts

Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Posted Friday 2/07/25 @9:39 AM — A quick update. While the GFS is forecasting 3-5 inches of snow beginning Saturday afternoon, ending before daybreak Sunday, my preferred model for mixed precipitation events, the NBM, is forecasting very low accumulations but a heavy sleet and rain event.

NBM forecast precipitation type 7 PM Saturday

Coming Active Weather Pattern

Posted Thursday 2/06/25 @9:49 AM — As mentioned in last Sunday’s post, a stalled frontal boundary through the middle of the country will become a focal point for storm development. Today’s frozen mix was the first of several disturbances that will affect our weather over the next week.

GFS forecast for early next Tuesday The colored thickness contours running east-west will be a focal point for low pressure development.

The next disturbance moves through late Saturday into Sunday morning. A thermal profile similar to today is expected, with snow, sleet, and rain changing to all rain by Sunday morning. This weekend storm has the potential for somewhat greater amounts of snow accumulation in our area.

Additionally, there’s a strong signal for at least one or two additional disturbances next Tuesday into Wednesday. The ECMWF is suggesting the potential for substantial snow during this time frame, although the AI model isn’t in full agreement.

A Messy Commute Early Thursday

Posted Wednesday 2/05/25 @5:37 PM —Little change from this morning’s posting. Light snow after midnight tonight changes to sleet and freezing rain around daybreak and then to all rain by late morning. The rain tapers off and ends between 2 and 3 PM.

Precipitation Type at 8 AM. White contour is 32° line

Posted Wednesday 2/05/25 @9:44 AM — Light snow and somewhat heavy sleet will transition to freezing rain and then quickly to rain between 6 AM and 9AM on Thursday, somewhat later far northern and northwestern suburbs. Accumulations of a coating of sleet and snow are still forecast to be up to an inch in some places, according to the NAM.

I’m still leaning towards the model blend (NBM) which has only about 1/2” in a few locations—

Today’s 12z NBM accumulation forecast
Snow Sleet and Rain Thursday

Posted Tuesday 02/04/25 @5:22 PM — After reviewing the latest model blend (NBM) and the ECMWF AI model, Thursday’s storm looks to be mostly sleet and rain, but starting as light snow with a coating to a half inch accumulation only. I think we need to disregard the Canadian model snow totals I posted earlier. The changeover to rain occurs during the rush hour, as posted yesterday.

Posted Tuesday 02/04/25 @3:20 PM — Some snow accumulation is looking more likely Thursday morning, despite a changeover to sleet, freezing rain and then rain by mid morning. The precipitation moves in early and departs earlier too. A total of near 0.5” water-water equivalent is expected to fall; if this were not to changeover, this might be 5”-6” of snow.

The GFS has this starting about 3 AM as a location-dependent mix—

Today’s GFS Precipitation type at 7 AM Thursday. White contour is the freezing line near the surface.

There’s an expected changeover to all rain by late morning, with the precipitation becoming spotty at that time. The thermal profile suggests a period of cold air damming, which may delay the changeover.

The actual vertical temperature profile will determine the actual snow accumulation, but in some areas, actual ice accumulation may be more important. Here’s the Canadian RGEM snow totals forecast—

Today’s 12z RGEM Snow totals by late morning Rrye

Posted Monday 02/03/25 @5:31 PM —Low pressure in the central US will move eastward and spawn a secondary coastal low near the Delaware coast before daybreak Thursday.

ECMWF AI forecast for 9AM Thursday



Temperatures in the mid levels of the atmosphere are forecast to be too warm for snow, but cold temperatures in the lowest levels will likely cause the precipitation to start as sleet and freezing rain, especially north and west of the city. This should change to all rain during the morning rush hour.

The rain should end by mid to late Thursday afternoon.

A somewhat similar situation will develop on Saturday. There are differences in the speed and timing of this system, but it’s looking to be primarily rain, again possibly starting as a mix.

Posted Monday 02/03/25 @ 10:52 AM —This week’s weather postings will be more sporadic than usual.

Originally Posted Mon @ 10:04 AM —

A frontal boundary to our south will become a focus for low pressure development later in the week. A storm system will move along this front from southwest to northeast late Wednesday into Thursday and again next weekend.

Slight changes in the intensity of the low pressure systems that develop along with changes in the position of the stalled frontal boundary will determine the precipitation type- snow- sleet-freezing rain-rain.

The current trend is for mostly liquid (rain) here in and around Philadelphia, but there are differences in the model forecasts, so uncertainty exists. Several models have snow changing to sleet and/or freezing rain Wednesday night. Too early to be sure.

ECMWF AI model—

ECMWF-AIFS forecast for Thursday at 7 AM. Freezing line at the surface (white) cuts through Philadelphia, but the magenta and red “thickness lines” to our north suggest this will be rain and sleet at this time, (Click on image for a larger view.)

By next Saturday, we’ll be in the warm sector ahead of an approaching cold front, according the the ECMWF-AI model—

ECMWF-AIFS forecast for Saturday night. Rain ahead of a cold front, but the (?) suggests the possibility that low pressure could develop again along the front. (Click on image for a larger view.)

An interesting set up. Stay tuned.

Philadelphia Area Weather Forecasts

WEEKEND WEATHER FORECAST

#Philadelphia #weather #PAwx

Posted Saturday 02/01/25 @ 3:48 PM — The rainfall we had Friday seemed more substantial than it was. Here’s the MRMS 24 hour rainfall totals based on rain gauges and radar calibrated to the rain gauges.—

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 forecast for Sunday is little changed. Cloudy for much of the day, except early morning and remaining slightly colder than seasonal averages with highs 37º-39º with higher than usual uncertainty (standard deviation).

Originally Posted Fri 5:04 PM —Following the rain Friday night, high pressure builds in for Saturday with cooler temperatures. On Sunday, low pressure to our north will bring clouds but no precipitation is expected here. Still seasonably cold.

Here’s the GFS forecast for Saturday—

Today’s 12z GFS forecast for 7 PM Saturday shows high pressure over us. Low pressure will move north of us on Sunday. (Click on image for a larger view.)

A seasonably cold day Sunday will be replaced by a mild day on Monday, followed by a cold front passing through Monday evening with colder weather returning for Tuesday.

By Monday—

GFS forecast for late Monday. Mild temperatures on Monday will be replaced by cold high pressure building in for Tuesday. (Click on image for a larger view.)

There’s still the possibility of rain on Thursday and another storm is again showing for Super Bowl weekend.

Saturday Forecast

Mostly sunny and somewhat seasonably cold. Windy in the morning, but winds gradually decrease during the afternoon.

NBM high temperatures: Blue Bell, PA 38º Philadelphia, PA 41º
Higher than usual uncertainty (based on standard deviation): ± 2.1º

Sunday Forecast

Some bright areas through clouds early, then mostly cloudy late morning and during the afternoon. Less windy

NBM high temperatures: Blue Bell, PA 39º Philadelphia, PA 42º
High then usual uncertainty (based on standard deviation): ± 2.4º

Philadelphia Area Weather Forecasts

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Friday Forecast Update

Posted Friday 01/31/25 @ 9:32 AM — A slight shift in the timing of the heavier rain today— late afternoon through this evening, ending after midnight. Total rainfall in the city and surrounding areas is now forecast to be less, closer to 0.30″-0.40″. Heavier rainfall in South Jersey.

NBM 12z Accumulated Rainfall for Friday into early Saturday. (Click on image for a larger view.)

The potential mixed precipitation storm I prematurely mentioned last evening has changed timing, from possibly next Saturday to possibly next Thursday. That’s a big change, suggesting the models, including the AI models, don’t yet have a good handle on things. Nonetheless, the setup ingredients appear to be there. Stay tuned.

Friday’s Rain Update

Posted Thursday 01/30/25 @ 6:01 PM — The rainy forecast for Friday hasn’t changed appreciably and rainfall totals are similar to the ECMWF forecast graphic posted yesterday. Rain begins about 3 AM Friday, earlier south and west and continues through about 9 PM Friday evening. It will be windy and gusty at times during the day, especially late afternoon when the heaviest rain is expected to fall.

The weekend looks as follows: Sunny on Saturday and cloudy on Sunday as a disturbance passes to our north.

No major storms until NEXT weekend, when things may get interesting, according to the AI models and the ECMWF—

The ECMWF forecast for Superbowl Weekend (NEXT Saturday) Very far off in the future, but the setup is for a mixed bag of very heavy precipitation here. (Click on image for a larger view.)
Friday’s Rain

Posted Wednesday 01/29/25 @ 7:42 PM — A storm bringing only rain to our area will move in several hours before daybreak on Friday. It will be rainy all day and the rain will taper off during the evening.

Continuing our ongoing trend towards lower than average rainfall, we’ll only see 0.50″ of rain in the immediate Philadelphia area according to the AI model. Areas not far to our south will receive over an inch, according to the latest models.

Staying with the AI model, here’s its forecast total rainfall for Friday—

Today’s 12z ECMWF-AIFS total accumulated rainfall by Saturday morning. (Click on image for a larger view.)

The NBM is forecasting heavier rainfall for Friday—

Today’s 18z NBM rainfall forecast (Click on image for a larger view.)
AI Model Looks Quite Good in Simple Experiment

Posted Wednesday 01/29/25 @ 5:47 PM — The temperature reached at Philadelphia airport today was 52º, 53º based on hourly records. ( If 53º was reached, it occurred off-hour and will be posted on the NWS site in a few hours.)

It’s very impressive that the AI model correctly forecast this range a week ago. Today’s NBM forecast was a still a degree so too cool.

Posted Wednesday 01/29/25 @ 9:39 AM —Over the past week, I’ve been conducting a simple observational experiment regarding today’s high temperature forecast. (Also see here.)

I chose to follow the AI model temperature forecast for today, because it was below freezing here at the time and the majority of the models, including my go-to model for temperatures (the NBM) were forecasting highs in the mid 40s for today, while the ECMWF-AIFS at that time was forecasting mid 50s! Quite a difference.

Incredibly, the regular model forecast have creeped upward towards the 50s and closer to the AI model while the ECMWF has shave off a few degrees to a high of near 53º.

Here’s the latest NBM —

Today’s NBM (12z) high temperature forecast for today. (Click on image for a larger view.)

Here’s the latest AI (ECMWF-AIFS) forecast for today—

Today’s ECMWF-AIFS high temperature forecast for today. (It should be noted that the ECMWF forecasts in 6 hour increments and the version I download does not include the day’s maximum temp. The only data is the actual temp at 1 PM as shown above. Since high temperatures typically occur around 3 PM, the actual max temp for today may be somewhat higher

What’s impressive is that the ECMWF-AIFS was forecasting this range of max temperatures almost a week ago! It took the computational models almost a week to approach its forecast.

Posted Tuesday 01/28/25 @ 10:53 AM — Radar shows some snow showers to our far northwest. Superimposed RAP model vertical motion (“omega”) shows strong downward motion, likely dissipating these snow showers greatly by the time they get to Philadelphia—

Radar shows some snow showers to our northwest. Superimposed RAP model vertical motion (“omega”- yellow dashed lines are negative) shows strong downward motion, likely dissipating these snow showers greatly by the time they get to Philadelphia (Click on image for a larger view.)

Posted Tuesday 01/28/25 @ 9:17 AM — When I went to bed last night, the forecast for Philadelphia on our news radio station called for “‘”snow showers, possibly reducing visibility” and clouds. Did I miss something with my update yesterday? What were they talking about?

We’ll have a mix of sun and clouds today. Several weak disturbances are in the pipeline for us over the next few days. Snow/rain showers are a slight possibility.

WV image with superimposed RAP model parameters. Disturbances 1-3 are in the pipeline to affect us. The upper level low (4) will bring rain on Friday. (Click on image for a larger view.)

There’s a chance that the storm on Friday may start as a bit of freezing rain or sleet here before a change to all rain. Not a certainty.

Posted Monday 01/27/25 @ 5:55 PM — A slight warmup for Tuesday and Wednesday. The ECMWF-AI model has us in the low 50s on Wednesday. The model blend (NBM), my go-to model for temperatures, now has a forecast high of 48º in Philadelphia with a rather large standard deviation of ± 2.8º.

A series of weak fronts and upper air disturbances come through over the next few days, specifically before daybreak Tuesday and Tuesday night. A rain maker is on the way for Friday, although the heaviest rain may move to our north and south.

The front and the system bringing rain on Friday are visible on water vapor imagery—

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. The closed low in the southwestern US will move into our area on Friday. (Click on image for a larger view.)

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Originally Posted Mon 10:45 AM —A split jet flow and a still somewhat chilly northwesterly flow will keep temperatures slightly above average through Wednesday, becoming somewhat colder Thursday, then warming again Friday with rain.

Today’s 06z NAEFS jet stream wind speed forecast for Wednesday morning. The upper closed Low (L) will eject towards us bringing rain by Friday. (Click on image for a larger view.)

Regular readers here know that over the past week, I’ve been watching the AI version of the ECMWF which has consistently forecast high temperatures on Wednesday to be in the low 50s! Every other model has us in the mid to upper 40s. So this is a little experiment to see if the AI model has any special insights into high temperatures—

Today’s 06z ECMWF-AIFS forecast temperatures on Wednesday. Much higher, and consistently so. then the regular models. (Click on image for a larger view.)

It appears we may have some rain on Friday into early Saturday. This feature has been in the forecast for several past days, with each model run moving it earlier. (It was originally forecast for this rain to move in Saturday into Sunday.)

Today’s 06z NAEFS forecast for Friday at 1 PM. The white contour is 32º, the red, yellow and magenta lines are critical thickness lines, indicating the average temperature of different lower levels of the atmosphere. With all of these lines to our north, we will have rain, not snow. (Click on image for a larger view.)

The weekend looks to be dry.

No significant snow storms are on the horizon for us. For that matter, we’re still running a rain/snow deficit and the dry conditions of last Fall have not shown signs of ameliorating to this point.