Posted Tuesday 01/20/26 @ 8:05 AM — A major long-duration winter snow storm is increasingly likely beginning Sunday. The ECMWF-AI and HGEFS (AI) models along with the GFS are all forecasting a major storm to move just south of us beginning late Saturday (most likely beginning early Sunday) and continuing possibly through Monday! The ECMWF is the slowest and strongest with this storm.
Today’s 06z ECMWF-AI model forecast for 7 PM Sunday. Our entire area will be north of the RED 500-1000mb thickness line, indicating all snow and temperatures are expected to be below freezing. (Click on image for a larger view.)
As is always the case, there are differences in the forecast northern extent of the system and in the speed. The GFS is much faster, the ECMWF is much slower, giving higher snow totals.
I’ll leave the heavy lifting at this point to the the model blend (NBM model) which, at last count, combines and statistically weights about 40 different models based on their performance over the previous six hours.
Here’s the current NBM snow forecast by Monday morning—
07z NBM forecast mean snow totals 7 AM Monday. White contours 1 inch increments. The storm may last longer than this! (Click on image for a larger view.)
The latest available ECMWF shows higher snow totals with the storm lasting into Tuesday. I’m not sure I believe it at this point in time.
This storm is still well in the future, weather-wise, and we’ve all seen these storm forecasts become big busts. And it might be sacrilegious to post potential snowfall this early in the week. But hey.. that’s why you visit this site. No hype, just the facts as I see it.
Stay tuned!
Cold! & Possible Snow Again this Weekend
Posted Monday 01/19/26 @ 4:51 PM — It’s winter in Philadelphia and it does get cold, and cold it will be. Earlier I posted the forecast low temperatures Wednesday morning.
The wind chill temperatures for tomorrow, Tuesday look impressively cold. (I often don’t “do wind chills” because I think it’s an opportunity to hype and conflate low temperatures on TV.)
That said, Tuesday morning at 8 AM looks to be very windy and cold with wind chills below zero!
Todays’ 18zRRFS calculated wind chill temperatures (“apparent temperatures”) at 8 AM Tuesday. Black Contours are 2º increments (Click on image for a larger view.)
Of interest continues to be a disturbance forecast to move just south of us, then develops off the coast late next Saturday through Sunday.
The HGEFS (AI Hybrid) and the ECMWF-AI are forecasting this storm. The latest NAEFS and the AIGFS currently show less snow with a more southern track. I’m keeping an eye on it.
Originally Posted Mon 9:50 AM —The cold weather that has arrived today and that will be reinforced with another front later today has been well-advertised. By sunrise Wednesday morning, we’ll have reached our lowest temperatures—
NBM Mean Low temperatures with standard deviation (uncertainty) at 7 AM Wednesday. The large standard deviation is typical for low temperatures, and in this case, the actual lows likely be below the mean temp. ( light blue contours are 2º increments) (Click on image for a larger view.)
Of interest this week is our next possible snow storm for next weekend, currently predicted by both the ECMWF-AI and the HGEF (AI) models. This storm is far in the future (at least as weather forecasting goes), but indications are that it will drop a minimum of 4+ inches and likely more if the current AI model forecasts are correct. The moisture source will be the Gulf of Mexico. There’s also a possibility of mixed precipitation at some point in the storm.
Here’s current ECMWF-AI forecast for next Saturday—
Today’s 06z ECMWF-AI forecast for 7 PM next Saturday. The precipitation (green shading) will be all snow at the start, as indicated by our being north of the red, yellow and magenta critical thickness lines. (Click on image for a larger view.)
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”.
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 Saturdaymorning. 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 Wednesdaynight. 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 blueL 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.
Posted Friday 01/09/26 @ 10:06 AM — Just as there was a dramatic change in the with Saturday’s high temperature forecast, a comparison of this morning’s models with the real time RTMA data suggests that the models are having some issues modeling today’s rain moving in.
Current (10AM) radar and Clear Channel (14) satellite image. The radar echos are closer than forecast by several models. (Click on image for a larger view.)
The actual observations (the RTMA) suggests that high pressure is blocking advance of the rain, while the advanced location of the line of showers west of our area suggests something quite different. The only thing I can say— there’s uncertainty with the amount of rain and its onset this afternoon.
It should be noted that the latest ECMWF is forecasting more rainfall this afternoon than was being forecast yesterday. Still going with 3-5 PM onset This continues to be an interesting system. Stay tuned.
Models guiding this forecast: HRRR, RTMA RRFS ECMWF
One More Thing
Posted Thursday 01/08/26 @ 7:54 PM — For days now, I (and everyone else) has been talking about temperatures reaching and exceeding 60º on Saturday. The forecast has changed significantly over the past 18-24 hours and the NBM (which is my go-to model for temperatures) has been slow to capture the trend.
The latest models from this afternoon (18z) are forecasting highs only in the mid 40s for Saturday due to an easterly flow instead of a previously forecast warmer southerly flow. The actual high temperatures will occur before noon on Saturday, dropping during the afternoon.
18z RRFS temperatures at 2 PM Fine black lines are 1º increments (Click on image for a larger view.)
Models guiding this forecast: GFS, NBM, RRFS , REFS, ECMWF-AI,
Rain moves in Late Afternoon Friday
Posted Thursday 01/08/26 @ 5:38 PM — The models have trended towards minimal/no rain before 4 PM for Philadelphia and its immediate western suburbs on Friday, somewhat earlier far western sections. Much of the day will cloudy, but a few bright intervals during the day. The Model Blend (NBM) is showing very light rain after 4 PM with totals less than 0.04″ but greater in western sections. Here’s the REFS forecast accumulation—
12z REFS forecast accumulated rainfall by10PM (Click on image for a larger view.)
Considerable rain for Saturday for most of the day. Clearing and sunny skies for Sunday.
Thursday through Sunday Outlook
Posted Wednesday 01/07/26 @ 11:30 AM — The forecast for above average temperatures through Saturday has been well-advertised. Here’s the NBM high temperature meteogram for Philadelphia—
12z NBM forecast Temperatures/Dew Points for grid point Philadelphia Center City. (Click on image for a larger view.)
Also as forecast, rain will move in on Friday, either early afternoon or mid to late afternoon.
There are differences between the models regarding the speed and development of this Friday system: The European and Canadian models are faster with rain moving in on Friday afternoon and much faster to move it out on Sunday.
The comparison below of the AIGFS and the ECMW-AI forecasts at 1 PM Sunday show significant differences:
Comparison of the rain coverage forecast for the six hours preceding 1 PM Sunday. AIGFS (slower) ECMWF-AI (faster). The Canadian GDPS-AI is somewhere in the middle of the two above.
If the AIGFS (and Canadian GDPS-AI) is correct, the Eagles will have to contend with some rain on Sunday. If the ECMWF-AI is correct, it will be mostly dry during the game.
Tuesday Update
Posted Tuesday 01/06/26 @ 9:34 AM —A low pressure system passing to our north this evening will bring a warm front through today followed by a cold front tomorrow. Despite the clouds this morning, it looks like sunshine through high clouds this afternoon.
Wednesday looks to be mostly sunny and quite windy. High 51º-52º
Thursday highs will be in the same 50-52º range during the daytime, but temperatures warm up further later Thursdayevening.
There’s a range of model forecasts for the rain expected Friday through Saturday. The GFS and the AIGFS is slower with the rain onset on Friday and slower for it to exit on Sunday. There’s also a question of weather the rain will be substantial or less than 1/2″ total.
Todays’s 06z GFS forecast for 3 PM Friday. Rain doesn’t move in to the city until mid to late afternoon. (Click on image for a larger view.)
Models guiding this forecast: REFS, NBM, GFS. AIGFS
Originally Posted Sun 8:37 PM —This week’s main ‘theme’ will be an increase in warmth, expected to begin in earnest on Wednesday.
18z NBM (model blend) meteogram for temperature/dew point for KLOM Blue Bell. High temperatures on a gradual but consistent climb to near 50º on Wednesday.(Click on image for a larger view.)
Several systems are expected to pass to our north with any precipitation also staying north, extending as far south as Berks county on Monday.
For the Philadelphia region and the Delaware Valley, considerable cloudiness is expected on Monday as the low passes to our north and warm moist air is brought in aloft. Highs remain in the 30s.
Another system passes to our north on Wednesday, that brings a weak cold front through. The chill down from this front will be short-lived.
A slowly moving cold front approaching from the west with waves of low pressure moving along it will pass to our northwest on Friday; most of the precipitation (rain) will pass to our northwest. Yet another wave of low pressure moves up the same path on Saturday.
18z ECMWF-AI forecast for Friday early afternoon. The area of rain moves to our northwest, just brushing our area. (Click on image for a larger view.)
While the general features of this weather outlook are consistent across models, it would not take much of change in intensity or track to greatly change our area’s forecast and weather. Stay tuned.
