Category Archives: Philadelphia Weather Outlook

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Posted Friday 03/14/25 @ 9:30 AM — This morning’s clouds weren’t accurately predicted by several models, most notably the GFS. Also missing this cloud forecast was the ECMWF-AI-Single. Higher resolution models — the HRRR and HRRR-dependent NBM along with the NAM-NEST did predict this cloudiness—

06z NBM model cloud cover forecast for now (9:29 AM). (Click on image for a larger view.)

All models have the clouds dissipating between 11 AM and 1PM. Saturday looks cloudy but mild. Light rain begins as early as mid-morning on Sunday. Details later today with my regular “Weekend Weather Forecast”.

I’m looking for signs that the experimental RRFS will return. Its model runs are currently on hiatus, being evaluated for operational release. Its current status is available in this .pdf from NOAA.

Thu 8:49 AM —Forecast Review — The ECMWF-AI-Single model continues to be impressive. Its forecast for some sunshine through a considerable high layer of clouds has so far verified, in stark contrast to the GFS and NAM-NEST forecasting a dark low cloud day, even with drizzle. After years of ‘doing the weather’, this AI model appears to be the most impressive advance in forecasting I’ve seen.

(Gee, I wonder whether the TV people providing the “exclusive” forecast will acknowledge the blown forecast for today? They often don’t, or they find some area within a 100 mile radius that actually had the dark low clouds forecast.)

Hey, it may be too soon to celebrate, and some low clouds might still roll in from the east. That said, the latest ECMWF-AI just available has clouds thinning and dissipating for even more sunshine this afternoon.

Latest ECMWF-AI-Single at 2 PM—

ECMWF-AI-SINGLE Cloud and Temperature Forecast for 2 PM Thursday. (Click on image for a larger view.)

If this new AI model continues to prove itself, I can reduce my data costs and eliminate many more models I download daily. (I’ve already eliminated downloading the HIRESW-FV3, the HIRESW-ARW, the HIRESW-ARW-MEM2, the RAP, and the SREF. )

Yet Another AI Model ‘Experiment’ Continued

Posted Wednesday 03/12/25 @ 10:52 PM —Tonight’s models are even more emphatic about low clouds Thursday morning into the afternoon. Tonight’s NAM-NEST even shows some drizzle. As I posted earlier, the AI model shows sun through thin high clouds. We’ll see what happens.

Posted Wednesday 03/12/25 @ 8:07 PM — We had a sunny day today (Wednesday), very close to the AI model forecast.

I’m still seeing many of today’s models forecasting low clouds for Thursday, but today’s ECMWF-AI-Single model runs have only high cloudiness for Thursday, albeit with a thicker high cloud layer than forecast yesterday.

The latest ECMWF-AI-Single model just became available and it keeps its sunshine through high clouds forecast intact—

ECMWF-AI-Single cloud forecast for noon Thursday. (Click on image for a larger view.)

Let’s see how it plays out tomorrow!

Yet Another AI Model ‘Experiment’

Posted Tuesday 03/11/25 @ 5:46 PM —The latest ECMWF-AI mode (single) and the latest GFS have very different forecasts for Wednesday and Thursday regarding cloud cover. An easterly flow behind a back door cold front may result in very cloud conditions.

Here’s the latest GFS cloud cover for Thursday noon—

18z GFS forecast for Thursday noon. Very cloudy and damp. (Click on image for a larger view.)

Here’s the ECMWF-AI-Single forecast for Thursday noon—

12z ECMWF-AI Single has little to no low clouds. Plenty of sun through high thin clouds. (Click on image for a larger view.)

The two forecasts couldn’t be more different regarding cloud cover. Ordinarily, with these forecasts, I would go with the GFS model. (The GFS relative humidity fields support a very dark cloudy mid-day. The NAM-NEST also is forecasting low clouds. )

The ECMWF-AI-Single model has really impressed me regarding temperature forecasts. It’s also done well with rainfall. Let’s see how Thursday’s cloud cover turns out. (Or whether the models come together.)

Posted Monday 03/10/25 @ 5:07 PM —A large ridge of high pressure in the central US with a split jet flow moving around this central high will continue to bring above average temperatures to our area.

Current (Monday afternoon) 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. Warm upper air ridge in center of the US. Split jef flow. The disturbance to bring rain late Saturday isn’t visible yet in this image. (Click on image for a larger view.)

Dry weather is expected to continue until late Saturday afternoon or evening.

Previously Posted Sun @ 5:03 PM — —The big story (and actually the only story) for the weather this coming week will be the warmer temperatures expected. Additionally, winds and wind gusts will be considerably lower than recent days.

For Monday, here’s the latest model blend (NBM). What’s interesting is how close the the ECMWF-AI model is to the NBM model with less computational effort.

18z NBM forecast high temperatures for Monday (Click on image for a larger view.)

By Tuesday, warmer temperatures push in from the southwest. We’ll be in the 67º-69º —

ECMWF-AI Single model temperatures at 2 PM Tuesday. (Click on image for a larger view.)

It’s been well-advertised about the 70º temperatures for this coming Saturday. The latest AI model suggests we may not reach that.

The change to Daylight Saving Time always takes some adjustment. For me, the biggest adjustment is the one hour later availability of weather model data. One hour doesn’t sound like much, but it brings models out a bit too late in the morning to be as useful and too late in the evening to make the 11 PM TV weather. I’ve written about this many times over past years—

Little Known Facts about Daylight Saving Time and TV Weather Forecasts

Daylight Saving Time and Weather Models

“Check Back at 11” — TV Weather and Daylight Saving Time

Philadelphia Weather Outlook

THIS WEEK’S WEATHER

#Philadelphia #weather #PAwx

Posted Thursday 03/06/25 @ 5:42 PM — The MRMS total rainfall graphic I posted in yesterday’s “Forecast Review” was posted before the storm had fully exited our area. Here’s the final rainfall totals for the region, which are impressive—

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.)

There isn’t much happening weather-wise over the next several days and into next week. We’ll be in a colder upper trough for some of the weekend. The next storm to affect our region may be next Thursday or Friday.

Wed 7:49 PM —Forecast Review —The majority of the rain has ended in the immediate PHL area. (There’s still heavy rain in NJ at this time.) Some additional showers are still possible this evening, Here is the MRMS rainfall summary for today’s rain.

The total rainfall was considerably greater than forecast by the models. The GFS was notably off.

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.)

It’s been a long time since we had such a heavy rain event.

Wednesday Forecast Update

Posted Wednesday 03/05/25 @ 4:16 PM — The HRRR, despite being a little slow with the first batch of rain, did well with the main line. Here’s what the radar looked like at 4:13 PM—

Radar image 4:13 PM. Very similar to the HRRR forecast shown below for 4PM (Click on image for a larger view.)

Posted Wednesday 03/05/25 @ 11:30 AM — Current radar shows the leading edge of rain much closer than the HRRR model has forecast. Even the 15z (10 AM EST) HRRR doesn’t show this.

I would expect the leading edge of the rain to be into Philadelphia within the next two hours. There is a line of heavier rain entering central PA. That might be the line of storms the HRRR is predicting for 5 PM.

Posted Wednesday 03/05/25 @ 8:25 AM — The models are consistently showing a strong line of storms with heavy rain and gusty winds to 50 mph coming through the city about 4 PM-

06z HRRR showing instantaneous precipitation rate at 4 PM

Addition showers possible during the evening hours. The actual cold front doesn’t come through until 2 AM Thursday morning.

Wednesday Forecast Update

Posted Tuesday 03/04/25 @ 8:49 PM — Tonight’s HRRR continues with a forecast of a line of storms moving through Philadelphia between 3 and 4 PM.

At 2 PM, the line is to our west, but with some break-out showers ahead of the main line—

Tonight’s 00z HRRR forecast for 2 PM Wednesday. The line is over Philadelphia at 4 PM. (Click on image for a larger view.)
Tuesday -Wednesday Forecast Update

Posted Tuesday 03/04/25 @ 9:14 AM — The models are forecasting these early morning clouds to dissipate by late morning. High temperatures 58º Blue Bell to 60º in the city.

The rain on Wednesday is now forecast to begin somewhat later in the morning as light showers. The heaviest rain now appears to move in about 3-6 PM with potential thunder and wind gusts approaching 50 mph.

Here’s the latest HRRR Precipitation Rate forecast—

Today’s 12z HRRR Precipitation Rate forecast for 5 PM Wednesday. (Click on image for a larger view.)

Posted Monday 03/03/25 @ 4:57 PM —A low pressure system is developing in the Rockies and will move northeast bringing rain on Wednesday. Here’s the current water vapor image—

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. (Click on image for a larger view.)

The latest models show a consistent forecast of rain moving in around 6-8 AM Wednesday. Before that time, warmer air ahead of the system will be with us on Tuesday with sunshine through high clouds. Highs on Tuesday 53º -56º (high uncertainty: ± 3º)

The rain on Wednesday is much-needed and the AI models are forecasting about 0.80 inches of rain, more far northwest and less into NJ. The deterministic ECMWF is similar, with localized 1″ amounts. The GFS model is only forecasting about 0.50 inches of rain, less into NJ. There may be pockets of heavier rain due to localized thunderstorms. Some high wind gusts possible beginning mid-afternoon Wednesday.

A cold front moves through about 1 AM Thursday morning. There may be lingering shower activity Thursday morning in eastern sections of NJ.

Originally Posted Sun 7:43 PM —Another cold day on Monday, followed by a warmup on Tuesday with temperatures rebounding into the low to mid 50s.

A storm is expected to move across the country and affect our weather on Wednesday with rain developing before daybreak.

18z 03-02-25 GFS forecast for Wednesday at 3 PM (Click on image for a larger view.)

We need some rain and unfortunately, the trend of the past few storms looks to continue, with the heaviest rain occurring to our far northwest.

This afternoon’s GFS shows the heaviest rain to occur to our far northwest on Wednesday. (Click on image for a larger view.)

Another trend has been for the predicted rainfall in our area to diminish with each subsequent model run. Yesterday, the total rainfall was predicted to be in the 0.8-1″ range around Philadelphia. The latest GFS posted above (in agreement with the ECMWF) has about half that amount forecast. (The latest ECMWF AI model still has about 0.8″ of rainfall here.)

I wish I could identify why this trend is occurring. It’s been going on since late last Spring.

Cooler weather returns for Thursday