THIS WEEK’S WEATHER | Philadelphia Weekend Weather & Storm Forecasts

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Battle of the Models – Snow?

Posted Friday 01/16/26 @ 9:47 AM —Currently, there is a cold front approaching from the Great Lakes area while an area of vorticity near Florida is expected to spawn a coastal low approaching to our southeast on Sunday.

As is often the case, the models vary in the track of the coastal low with a potential of [light] snow Sunday.

Current Radar with RAP model parameter overlay. Fine violet contours are potential vorticity. (Click on image for a larger view.)

First, on Saturday, we will likely see snow ahead of a cold front. Light intermittent snow begins in the morning and tapers off in the mid afternoon. Despite the forecast for temperatures to be above freezing, the precipitation will fall as snow or wet snow except in eastern NJ. Here’s the RRFS calculated snow accumulation—

06z RRFS calculated Snow accumulaton by 4 PM Saturday. (Click on image for a larger view.)

On Sunday, low pressure is expected to be spawned to our southeast and low pressure will track to the northeast. The current AI models show our area receiving snow, while the ECMWF, RRFS and to some extent, the latest GFS has the snow only affecting a small section of coastal NJ. On the otherhand, we have the AI models which all show some part of the Philadelphia area closest to I-95 corridor receiving some light snow, perhaps as much as an inch.

Here’s the latest 13z NBM with the mean snowfall for both Saturday and Sunday combined—

13z NBM shows some additional snow around Philadelphia on Sunday with most from Saturday. The accumulations near the shore are from Sunday’s coastal storm.(Click on image for a larger view.)

Updates later today with my weekly “Weekend Weather Forecast”.

Models guiding this forecast: GDPS-AI, NBM, RRFS , REFS, ECMWF-AI, HGEFS ECMWF-AI GFS

Two Chances for Light Snow this Weekend Continues

Posted Thursday 01/15/26 @ 4:44 PM — A deep trough in the upper flow has resulted in an area very strong potential vorticity where the jet stream rounds the base of the trough—

Water Vapor Channel 9 -Thursday afternoon with superimposed RAP model parameters. Fine violet contours indicate potential vorticity. The base of the trough is outlined by the white square box. Areas of low pressure will develop in this area and move northeastward. The first on Saturday brings light snow. The second on Sunday brushes us with some more light snow. (Click on image for a larger view.)

As is seemingly always the case, there are differences in the model forecasts.

With the exception of the ECMWF, most models point towards light snow on Saturday morning. Temperatures will be at or just above freezing, so accumulations with melting will be difficult to pin down, but a coating to an inch is possible, especially areas north of the city. This will be a wet snow near the city and accumulations will likely be minimal.

18z GFS (just available) shows an area of precipitation moving through at 10 AM Note the position of the three “critical thickness” lines (red yellow, violet) which are east and south of our area, indicating what falls will be snow, even if the near ground temperatures are at or above freezing. (Click on image for a larger view.)

On Sunday, a more significant disturbance develops and moves northeast. Most models have this moving to our east, but the AI models consistently show the Philadelphia area gets brushed with light snow.

ECMWF-AI Forecast **Sunday** at 1 PM. Precipitation shield just makes it into Philadelphia and especially NJ. Notice the position of the three “critical thickness” lines (red yellow, violet) which are east and south of our area, indicating what falls will be snow, even if the near ground temperatures are at or above freezing. (Click on image for a larger view.)

Again, snowfall should be light with accumulations difficult to predict at this time. Stay tuned for updates.

FYI- The latest Canadian models show a heavier mix on Sunday.

Two Chances for Snow this Weekend

Posted Wednesday 01/14/26 @ 5:37 PM — The approaching cold front this evening is somewhat moisture-starved. Combined with warm temperatures, no snow is expected over night into Thursday.

The upper level deep trough will be a breeding ground for additional disturbances to form and to track up towards us this weekend. There’s considerable uncertainty regarding the tracks of these disturbances.

Least impressive is a disturbance that may bring light snow Saturday early afternoon. The Canadian GDPS with “AI Spectral Nudging” along with the latest RRFS are forecasting the possibility of light snow—

Today’s Canadian GDPS with “AI Spectral Nudging” forecast for 1 PM Saturday. (Click on image for a larger view.)

More impressive, but with higher track uncertainty is a low pressure system expected to form and move up towards us on Sunday—

Today’s 18z AIGFS forecast for 1 PM Sunday. It should be noted that the greatest uncertainty is a more westward track. (Click on image for a larger view.)

This Sunday storm is forecast by the AIGFS, the HGEFS and the GFS, but in all cases, we’re on the western fringe of the precipitation shield. The ECMWF and the Canadian GDPS-AI keep the storm further east, mostly missing our area. The greatest uncertainty shown by the ensemble models is west of the mean low.

We’ve already seen that the forecast for tonight’s snow has fallen apart. We’ll see how things evolve in the coming days for the next potential possibilities of winter weather. Stay tuned.

Wednesday Thursday Update

Posted Wednesday 01/14/26 @ 11:02 AM — A quick update. The models have backed off on the precipitation considerably in our area. Very little precipitation falling as light scattered rain showers is expected about 1-3 AM Thursday morning. No accumulations expected in the Philadelphia area with ground temperatures above freezing. Winds pick up before daybreak tomorrow. Quite gusty.

Thursday’s Non-Event

Posted Tuesday 01/13/26 @ 8:38 PM — Today’s models continue the trend for a ‘non-event’ on Thursday. While there is still some uncertainty in the east-west position of the low pressure development, all models have it occurring north of our area, keeping precipitation amounts to less than 0.18″ water equivalent.

Much of the precipitation will occur as light rain ahead of a cold front Wednesday night. A changeover to some scattered rain-snow mix and to snow showers will occur early Thursday morning, about 5 AM, and will end about 9 AM. With ground temperatures above freezing, little to no accumulation is expected with less than 0.25″ snow falling. Winds increase Thursday morning with the front.

Here’s the Model Blend (NBM) mean snowfall forecast, with most areas getting possibly a wet coating at best—

00z NBM mean snowfall forecast by Thursday morning. Maybe a scattered coating, maybe nothing. (Click on image for a larger view.)

Moving back to tonight, there’s a chance of some widely scattered light sprinkles or rain showers tonight (Tuesday). Wednesday is looking cloudy with light showers in far western sections (Lancaster/Berks counties).

Thursday looks to be windy and cold.

Thursday’s Potential “Storm” Downgrade

Posted Monday 01/12/26 @ 5:28 PM — Today’s models have backed off from low pressure development and the latest model trends explain the high uncertainty seen with yesterday’s ensembles.

The system that will affect us Wednesday night into Thursday morning appears to now mainly to be associated with strong cold front with a rain-snow mix changing to snow before ending. (Low pressure that had been expected to develop near us Thursday appears to happen north of our area according to the latest Canadian and US models. The latest ECMWF available still has weak low pressure development, but there’s a model multi-hour time lag for their free “open data”. Their afternoon data won’t be available until 7:45 PM.)

Here’s the latest GFS model—

Today’s 18z GFS shows the deep dip in the jet stream and a poorly defined Low pressure system far north of our area. (The **blue** L 541 is the upper level low, which always hangs back from the surface low.) (Click on image for a larger view.)

The latest Model Blend (NBM) still shows low to minor snow accumulations, similar to those I posted this morning. Even with rain changing to snow, actual accumulations will be challenging with melting on warmer ground and with mixing.

Backing up a bit, the clouds that affected parts of our area today (Monday) were associated with warmer moisture moving aloft, sort of a pseudo warm front. Tuesday will be milder than Monday with temperatures from 48º to 50º.

There may be some light showers around midnight Tuesday night into Wednesday. Then mostly cloudy.

Thursday’s Potential Snow looking to be Minor

Posted Monday 01/12/26 @ 9:07 AM —Thursday’s storm continues to be uncertain but is trending towards low to minor accumulations.

The latest HGEFS (Hybrid AI) ensemble model shows the storm to develop somewhat north and east of our area, causing us to miss any potentially heavy snow.

At the same time, there continues to be areas of uncertainty based on the forecast spread of the 62 model variations that make up the HGEFS—

Today’s 06z HGEFS AI model. L is the mean position of the surface low, based on 62 model variations. The ? indicated areas of high spread (uncertainty). (Click on image for a larger view.)

The areas of uncertainty away from the mean position indicate possible areas of additional low pressure development, unknowns in speed and depth of development, unknowns in track.

The latest NBM (12z) just available shows this for the current mean snowfall accumulation by Friday morning. (The NBM (Model Blend) is based on a statistical treatment and weighting of about 40 models based on their performance predicting the weather 6 hours earlier.) —

12z NBM mean snow accumulation by Friday morning. (Click on image for a larger view.)

My impression is that you won’t need the snow blower for this snowfall. Yet there’s plenty of time for the forecast to become more certain. Stay tuned.

Possible Storm Thursday

Originally Posted Sun 9:13 PM —High pressure has built in on Sunday with the return of cold temperatures, as the jet flow is in a trough configuration over our region.

This dip will be short-lived, as it is expected to flatten on Tuesday with relatively milder air returning for Tuesday and Wednesday.

HGEFS (AI) model shows a flattening of the jet stream, as reflected in the **RED** 500-1000mb thickness contour. The blue arrow points to the next reload of cold air that will push the jet flow into a significant trough by Thursday.

By Thursday, cold air has reloaded from Canada and the jet flow is pushed into a very deep trough—

HGEFS (AI hybrid ensemble model) shows a deep trough with low pressure directly over us by Thursday morning. Notice that the white and yellow contours are north of our area, **indicating temperatures near ground to about 2000 ft are above freezing to the south of these lines.** (Click on image for a larger view.)

There’s much uncertainty with the evolution, position, path and expected intensity of this low at this time. This is reflected by the latest ECMWF- Ensemble model showing standard deviation (uncertainty) —

12z ECMWF-ENS surface pressure with standard deviation (Click on image for a larger view.)

This amount of uncertainty is not unusual in this time frame, but since the high standard deviation is not where the mean low pressure location is, it suggests that there are issues in modeling the position and evolution of this storm.

At the current time, this does NOT look to be a significant storm. Light rain, wet snow and graupel Wednesday night changing to light snow during the day is my current bet. 1/2 – 2 inches possible. Again much uncertainty. Stay tuned for updates.