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About This Snow
Posted Thursday 03/12/26 @ 2:55 PM — Back on Tuesday morning when I first posted that “I wouldn’t be surprised if we see some snow flurries” morning, I thought I was being a bit risque with the forecast. I based it only on the position of the critical thickness levels.
The amount of wet snow is more than I would have guessed and it’s possible we’ll even see a light coating , as temperatures have already fallen faster than previously forecast. Precipitation continues to about 5 PM in Philadelphia and later in NJ so we’ll see if grassy surfaces get a coating or more.
Severe Storms Increasingly Likely
My regular table of severe parameters was better at suggesting this wasn’t a particularly severe system.
Expect more scattered showers tonight and through much of Thursday. Again, I wouldn’t be surprised if we see some snow flurries late afternoon or early evening on Thursday.
Updated Wednesday 03/11/26 @ 7:16 PM — The latest RRFS hourly shows the line of storms reaching Philadelphia and blossoming and stalling for a few hours as weak low pressure forms. Storms may linger from about 8 PM through almost midnight.
Posted Wednesday 03/11/26 @ 4:52 PM — We had some showers move through early this afternoon, as forecast by some models. The main event remains for this evening into tonight.
According the latest RRFS and HRRR, a line of heavy and likely severe storms will move through between 8 PM (western suburbs) and 10 PM (NJ). There are many way of quantifying potential severity. One is the SWEAT Index (Severe Weather Threat Index) which looks at winds, dew points and temperatures. Here’s the RRFS SWEAT index of 9 PM—
Before the main event line of storms arrive, there are several areas of moderate to high helicity (600 m2/sec2) indicating possible strong rotating winds.
Despite some of these numbers, CAPE is moderate to low (350-450 joules) and Vertical Shear is moderate (25). We see much higher determinants of severe weather most summers. Here’s a comparison to give a feel for tonight’s severity.
| Severity Parameter (HRRR) RRFS |
Sept 1 , 2021 Tornado Outbreak (example of highly severe) |
4-1-2023 Tornadoes (Example of severe) HRRR |
TODAY |
Notes |
| CAPE Joules/kg |
3500-4200 ⚑⚑⚑⚑ |
2100 ⚑⚑ |
450 ⚑ |
|
| Helicity m^2/s^2 |
1350 ⚑⚑⚑⚑⚑ |
655 ⚑⚑ |
650 ⚑⚑ |
Delaware |
| Vertical Shear 1/sec |
40-46 ⚑⚑⚑ |
40-45 ⚑⚑⚑ |
23-25 ⚑ |
|
| Precipitable Water | 2.7″ ⚑⚑⚑⚑ |
0.83” ↓ |
1.8″ ⚑⚑ |
|
| Lifted Index º K |
minus 6º ⚑⚑ |
minus 9.3º ⚑⚑⚑ |
minus 3.1º ⚑ |
|
| HRRR Hail inches |
1.9 ⚑⚑ |
1.4 ⚑ |
1.6″ ⚐ |
|
| Peak Wind Gusts mph |
40-50 ⚑⚑ |
40-50 ⚑⚑ |
25 mph ⚑ |
|
| Storm Motion Shear Vector Alignment |
Aligned – ~ 90º ⚑⚑ |
Almost aligned ⚑⚑ |
Partly aligned ⚑⚑ |
|
| 250 mb Jet Stream Wind mph |
63 ⚑ |
135 ⚑⚑ |
67 |
|
| Max Updraft Velocity m2/s2 |
135 |
NJ | ||
| Max 600 mb DZDT |
50 m/s |
↓ indicates works against Severity ⇩ Significant, but less impact
We’ll see what happens.
More rain later tonight into Thursday afternoon as low pressure develops along the front.
Severe Weather Possible
Posted Wednesday 03/11/26 @ 8:52 AM — A complex system will affect our weather from later today through much of Thursday. An approaching cold front with a sharp change in temperatures will move towards us with showers and thunderstorms. The front slows up as a secondary low pressure system forms along the front, causing rain to linger into late afternoon Thursday.
Current conditions:
After reviewing the latest RRFS, HRRR and GFS models, it appears that
- Strong/severe thunderstorms will likely move through around 5-6 PM with strong wind gusts.
- High Helicity and vertical motion could produce tornadic activity.
- Additional rounds of showers and thunderstorms will move through later this evening between 8 PM and midnight.
- There may be a lull around midnight before rain re-develops from a secondary low developing on the front.
- Rain continues through Thursday, ending late afternoon
- A few snow flurries possible as the rain ends
Luckily, the jet stream configuration is not ideal, so we may be spared a very severe outbreak.
This is system is complex and I expect to that changes in the details of the forecast will be necessary. Updates later today.
Wednesday -Thursday Forecast
Updated Tuesday 03/10/26 @ 11:00 PM — Tonight’s models have moved the timing of the thunderstorm line to 9-11pm near Philadelphia.
Posted Tuesday 03/10/26 @ 7:47 PM — An approaching strong cold front with plenty of energy along with a disturbance from the southern jet stream will combine to give us a prolonged period of rain and even thunderstorms late Wednesday through much of Thursday.
First, the possibility of earlier afternoon scattered showers and thunderstorms is still forecast by the Model Blend. However, most models are keeping the rain in our area to move in after 5 PM.
Rain, thunderstorms and strong wind gusts are likely over Wednesday night into Thursday morning. The GFS is somewhat faster with showers breaking out by 6-7 PM. This system will be slow to get going.
The actual front and wind shift occurs about 1 AM Thursday morning, however, the RRFS shows a line of severe storms with wind gusts 40-60 mph at 7 PM—
The front moves through slowly and rain is likely to linger into Thursday afternoon if a secondary low forms along the front. It would not surprise me if this system ends with some snow flurries late Thursday afternoon or evening.
This will be an active and interesting system. Stay tuned for updates!
Regular Visitors to this site know I generally update between 5 and 6 PM. Due to the change to Daylight Saving Time, many important afternoon models are not available until after 6-7 PM. Later updates, like this one, will be more typical.
Tuesday – Wednesday Forecast Update
Posted Tuesday 03/10/26 @ 9:31 AM — As indicated yesterday, the mean high temperatures forecast by the NBM continue to have large standard deviations (today ± 5º). Based on this, here’s my current forecast for today’s high temperatures:
Continuing with the trend from yesterday, it appears that light showers will move in on Wednesday, earlier than previously expected. Some shower activity, especially west of I-95 expected as early as 1-2 PM. This will keep temperatures in the 74º-77º range with some clouds. There’s a chance of some thunderstorms after midnight.
A Quick Update
Updated Monday 03/09/26 @ 10:08 PM — Temperatures have been running higher than the Model Blend (NBM) mean on many occasions. For Tuesday, like today, the NBM mean high temperature likely underestimates what we’ll see. The NBM mean PLUS the standard deviation brings forecast the right in line with the ECMWF-AI. Highs on Tuesday now look to be closer to 78º!
Enjoy Tuesday while you can. The models are hinting at an earlier arrival of showers and clouds on Wednesday, perhaps as early as late morning but more likely 2-3 PM in the afternoon. Temperatures on Wednesday will drop a few degrees from Tuesday’s highs. Updates tomorrow morning.
Originally Posted Sun 5:41 PM — The warmup expected this week has been well-advertised and is much anticipated. A warm flow of air will move into our area—
As a result, Water Vapor Temperatures indirectly reveal height, called the “effective layer” of the water vapor in a region, therefore revealing the mid and upper level 3D contours of systems.. Colder temperatures (blue- grey – white) indicate higher altitude, sometimes revealing upward motion. Red- Orange indicates warmer temperatures and a lower height for this layer. There are several water vapor “channels”; the one I display here is called the mid level height channel referred to as channel 9. (Click on image for a larger view.)
Here’s the ECMWF-AI forecast for early Tuesday morning. A warm southwesterly near surface flow of air will bring temperatures into the 70s—
By Wednesday afternoon, a cold front will approach from the west. We may see some showers late Wednesday afternoon and rain in the evening.
Here’s the NBM temperatures/dew points for Blue Bell PA —
Daylight Saving Time
A shift to Daylight Saving Time wouldn’t be complete without my rant about weather model availability with DST in the eastern time zone. Here’s my commentary from past years—
I’d like to update and clarify some of the information from previous posts.
| Model Name | Forecasts out to (hours) | Availability EST | Availability DST |
| HRRR | only 48 hours | 9 PM | 10 PM |
| NAM | 84 hours | 9:40 PM | 10:40 PM |
| NAM-NEST | only 60 hours | 9:35 PM | 10:35 PM |
| GFS | 24 hours | 10:55 PM | 11:55 PM |
| GFS 5 days | 120 hours | 11:20 PM | 12:20 AM |
| RGEM | 84 hours | 10:35 PM | 11:35 PM |
| ECMWF 5 days | 120 hours | after midnight | after midnight |
| RRFS | 84 hours | 10:45 PM | 11:45 PM |
| ICON 5 days | 120 hours | 11 PM | midnight |
| AI models | 120 hours | after midnight | after midnight |
You can see that any 5 day forecast isn’t available during the 10 PM EDT or 11 PM EDT news broadcasts. Their next day forecast update is also based on limited model data. Also, remember that this is when the models become available for download. They need to be downloaded and post-processed and reviewed. The NWS office in Mt Holly doesn’t update their forecasts until 3-4 AM in the morning based on the night’s models (00z = 8 PM EDT) While the NBM is hourly, its major revisions based on the 00z models occur 6 hours later, about 2 AM.
