Previous postings about this snowfall from the past several days can found here.

Monday Snow Update

Posted Monday 01/06/25 @ 10:21 AM — While the NBM model updates hourly, its 01z 07z 13z 19z model runs include newly precip precip data. The previous posting was the 12z NBM.

Here’s the 13z NBM (8AM) with refreshed precip data. Additional snow totals from 10AM forward—

Posted Monday 01/06/25 @ 9:31 AM — The snow began as forecast and should continue light through noon, then become spotty in the afternoon and taper off.

Here’s the additional snow accumulation from 7 AM onward, based on the NBM. (Add to what already fell in your location at 7 AM.)

Final Snow Accumulation Call

Posted Sunday 01/05/25 @ 5:34 PM — There’s a solution to the snow forecast dilemma. The Model Blend (NBM) initializes with the HRRR, combines many models (last count 43) and statistically weights each based on how well each did forecasting the previous 6 hour period. It also weights each model based on their overall track record. Quite a process.

Here’s the latest NBM with a precipitation update—

The above is in line with the latest GFS and is where I would hang my hat on tomorrow.

Snow Lovers to be Disappointed Monday?

Posted Sunday 01/05/25 @ 4:07 PM — It’s not very often that I can correct a subject heading simply by adding a question mark! At this website, you actually get to see the (forecast) sausage being made.

First, snow moves in from the southwest between 3 AM and 6 AM and tapers off to snow showers during Monday evening.

The afternoon models have trended back towards slightly higher snow totals in the Philadelphia region. Here’s the latest NAM, my preferred model for snow when there is blocking high pressure to the north—

The HRRR, a much more advanced model than the NAM, has been the most consistent over the past two days with consistently higher forecast snow accumulations. As you’ll see, there’s quite a difference in forecast amounts—

The ECMWF also shows snow, but there’s an 8 hour delay in release of their free data, so this model run is from 7AM (12z) this morning—

I don’t think any single model is going nail it down but an average of the NAM and HRRR looks about right.

Posted Sunday 01/05/25 @ 12:21 PM — After reviewing the new GFS, RGEM and HRDPS, the threat of a moderate snowfall on Monday is no longer on the table. I’ll post new graphics later, but about 1 to 1.5” near the city, less north, and about 2 possibly 3 inches southern Delaware and Chester counties.

Posted Sunday 01/05/25 @ 9:48 AM — As has been the forecast trend over the past day, high pressure nosing down from the northeast will greatly limit moisture from moving into our area. Several global models first caught this trend but some of NOAA models were slow to pick up on it.

The models are all moving in the same direction now. Here’s the latest NAM snow forecast—

The NAM-NEST has even less—

Blocking High Pressure to Limit Snowfall in Philadelphia

Posted Sunday 01/05/25 @ 7:40 AM — As mentioned over the past day, most models, especially the ECMWF, Canadian RGEM and German ICON, along with the ECMWF- AIFS model and several ensemble models have forecast blocking high pressure to nose down into the Philadelphia area from the northeast and block moisture from moving aloft over us. Less snow than previously forecast is the result.

The NAM, NAM-NEST, NBM and last night’s HRRR were still predicting moderate snowfall for us.

Here’s the current setup—

Previously Posted Saturday 01/04/25 @ 10:05 PM — A quick update with tonight’s latest 00z models, the NAM and the HRRR. The NAM continues in the general moderate range as seen earlier—

The HRRR is an eye-opener and possibly a single model run error—

Updates Sunday morning after 9:45 AM with the newer 12z models.

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Previously Posted Saturday 01/04/25 @ 5:05 PM — I’m glad I gave this the title of “Potential Winter Storm”, since more and more models are forecasting high pressure to nose down from the northeast, blocking any significant snowfall in our area and to our northeast.

The European (ECMWF), Canadian RGEM and German ICON models are now forecasting a minimal snowfall for Philadelphia on Monday. However our US -NOAA models continue to forecast a moderate snowfall.

Perhaps the most striking in the low range is the RGEM, which just became available and shows little to no snow!—

The latest ECMWF that’s available is from this morning. It also trends towards low snow totals—

The GFS is still predicting a moderate snowfall—

Previously Posted Saturday 01/04/25 @ 11:51 AM — This morning’s (06z) ECMWF continues to show much less of a snow shield north of this system. Here’s its snow forecast—

Previously Posted Saturday 01/04/25 @ 9:16 AM — There are differences between the European Model (ECMWF) and the NOAA models, with the NOAA models forecasting a more northern shield of precipitation (snow) than the ECMWF. The ECMWF forecast has the low pressure system to our south—

I’m inclined to stay with our NOAA models.

Reviewing the latest NAM and NBM, here’s the latest snow accumulation forecast—

Here’s the latest NBM forecast—

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Previously Posted Friday 01/03/25 @ 9:56 PM A quick update. After looking over the afternoon models, and tonight’s NAM, the trend has been for a southern track for the heaviest snow. The global ensemble (statistical) models are remarkably similar with similar areas of uncertainty in position and speed of the system.

I’m posting the latest snow forecast, based on the latest NAM model which just became available—

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Previously Posted Friday 01/03/25 @5:51 PM —There remains uncertainty with the final track of the storm and the degree of intensification. The general trend has been for a track that’s further south, giving the Philadelphia region less snowfall than had been predicted yesterday.

Here’s the current GFS forecast, showing several low pressure centers.

Here’s what I’m calling for, based on the latest NBM precipitation forecast—