Central PA Winter 25/26 Discussion and Obs

[Ruin]

Also I keep hearing about how warm the ocean is and thats another reason why the warm air wins out for some areas turns it to sleet. But we are in the heart of winter and its been pretty cold even before this artic blast. But the funny thing about that is the temps are colder now then what they have been for other storms and they didnt say anything about the ocean temps then??

[SnowPlowGuy88]

Been watching a live stream on YouTube on and off. Already seeing this over perform in terms of snowfall in places like Arkansas and Kentucky. My BIL in Kentucky had to go out a few hours earlier than expected to do snow removal. Hopefully that translates down the line, when we get in the goods. Back to my pre storm nap lol

[Itstrainingtime]

Horst just posted and said he'd have more to say this evening, but he's going 8-12" in Lanco with 10-16" (easily) north of the pike. 

[Itstrainingtime]

MU slashes Lanco to 6-12".

Okay...heading out on Duval Street. Should be an interesting evening here and back home.

[pasnownut]

1 hour ago, Jns2183 said:

The statistical distribution of the 18 model forecasts for Harrisburg reveals a tightly clustered consensus with a specific high-end skew, indicating that while a significant winter storm is certain, the exact "boom" potential remains tied to moisture efficiency. The ensemble mean of 12.72 inches serves as the mathematical anchor, but the standard deviation of 3.11 inches highlights a notable disagreement between model families. Specifically, regional models like the NAM and SREF are pulling the distribution toward the 90th percentile of 16.38 inches, whereas global models like the GDPS and ICON remain more conservative near the 11th-inch mark. This spread suggests that the primary forecast challenge is not the track of the storm, but the Snow-to-Liquid Ratio (SLR); models predicting lower totals generally expect a warmer, denser "heart-attack" snow, while the high-end outliers assume a colder, fluffier accumulation.
The implications of this distribution, particularly when viewed through the lens of the Z-score mapping, suggest that the "most likely" outcome is not a single number but a high-confidence corridor. The data shows that 68% of all model guidance (the +/- 1.0 standard deviation range) falls between 9.61 and 15.82 inches, creating a very stable target for infrastructure planning. The fact that the Mean Absolute Deviation (MAE) is a relatively low 2.36 inches indicates that the models are in better agreement than typical for a complex transition-zone event. However, the 100-mile Northwest bias observed in Arkansas—where models like the NAM missed the core entirely—suggests that the statistical "tail" of the distribution should not be ignored. If the storm over-performs its moisture transport as it did upstream, the 17.38-inch mark (+1.5 sigma) is a scientifically plausible outcome rather than just an outlier.
Based on this statistical synthesis, the final forecast range for Harrisburg is set at 11 to 16 inches, with a localized "boom" potential of 18 inches if the higher SLRs verify. This range captures the bulk of the probability density, spanning from the 25th percentile (11.35") to just below the 90th percentile (16.38"). The lower bound is protected by the consistent 1.00"+ QPF (liquid equivalent) seen across almost all guidance, which provides a high floor for accumulation. Conversely, the upper bound is capped by the warm-nose intrusion observed in the regional NAM runs, which currently prevents the consensus from shifting entirely into the 20-inch category.



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Youre a friggin wiz kid....

even if youre not a kid.

Impressive work bud.  

[Blizzard of 93]

18z Euro might be the best run yet for this event! Wow!

[Blizzard of 93]

18z Euro is all snow for everyone through 1 pm tomorrow. Then by 4 pm, only southern York & Lanco begin to mix.

[CASH_COOP]

2 minutes ago, Blizzard of 93 said:

18z Euro is all snow for everyone through 1 pm tomorrow. Then by 4 pm, only southern York & Lanco begin to mix.

can you post qpf total.  looks juiced up

[Blizzard of 93]

18z Euro only mixes turnpike & south by 0z & then mix creeps slightly further north by tomorrow evening as things begin to wind down.

[Blizzard of 93]

Just now, CASH_COOP said:

can you post qpf total.  looks juiced up

How about this first….wow! 
I’m sure it’s overdone a bit, but even even 75% of this would be impressive.

 

[GrandmasterB]

Absolutely razor thin margins down here. Nowcasting will be important. 

[Blizzard of 93]

3 minutes ago, CASH_COOP said:

can you post qpf total.  looks juiced up

Juiced up!

[CASH_COOP]

1 minute ago, Blizzard of 93 said:

Juiced up!

def wetter.   if that verifies there will be a 20"+ report in sc pa, right above mixing line.

[CarlislePaWx]

2 minutes ago, CASH_COOP said:

def wetter.   if that verifies there will be a 20"+ report in sc pa, right above mixing line.

Don't forget for the contest I predicted 19.59" of snow.  Maybe I still have a shot at this?

[mahantango#1]

8 minutes ago, Blizzard of 93 said:

Juiced up!

We need this for the drought 

[WmsptWx]

How close are we to game time? I am in State College currently.

[Jns2183]

I made a leading indicator watchlist for tonight starting at 1am

This Final Accumulation Decision Matrix is designed to give you a definitive forecast range for Harrisburg based on which leading indicator stations verify tomorrow morning.

Key Decision Thresholds for Tomorrow
* The 5:00 AM "Lynchburg Check": If KLYH (Lynchburg) is still reporting pure snow at 5:00 AM, the NAM's 11:00 AM sleet arrival for Harrisburg is effectively impossible. You can immediately shift your planning toward the 15"+ range.
* The "Sleet Ratio" Penalty: For every hour the "warm nose" arrives earlier than 6:00 PM, you lose approximately 0.6 to 0.8 inches of potential snow accumulation as the ratio drops from 13:1 to 6:1.
* The QPF Floor: Regardless of the timing, all high-resolution models agree on a liquid equivalent (QPF) of 1.0" to 1.3" for Harrisburg. This guarantees that even a "sleet-heavy" outcome will likely result in at least 9–10 inches of dense, frozen mass.
Final Forecast Recommendation
Stick with the 11"–16" range as your baseline, but keep a close eye on Fredericksburg (KEZF). That station is your "Early Warning System"—if they are still snow at 8:00 AM, the HRRR's 18-inch solution is no longer just a possibility; it becomes the most likely outcome.





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[Jns2183]

For closer

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[Ruin]

Hope the radar fills in more a little gap between the system 

[Jns2183]

The 18z NAM had the sleet line coming from Westminster Maryland to Harrisburg in 1 hour, which is absolutely flying



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[GrandmasterB]

36 minutes ago, Jns2183 said:

I made a leading indicator watchlist for tonight starting at 1am

This Final Accumulation Decision Matrix is designed to give you a definitive forecast range for Harrisburg based on which leading indicator stations verify tomorrow morning.

Key Decision Thresholds for Tomorrow
* The 5:00 AM "Lynchburg Check": If KLYH (Lynchburg) is still reporting pure snow at 5:00 AM, the NAM's 11:00 AM sleet arrival for Harrisburg is effectively impossible. You can immediately shift your planning toward the 15"+ range.
* The "Sleet Ratio" Penalty: For every hour the "warm nose" arrives earlier than 6:00 PM, you lose approximately 0.6 to 0.8 inches of potential snow accumulation as the ratio drops from 13:1 to 6:1.
* The QPF Floor: Regardless of the timing, all high-resolution models agree on a liquid equivalent (QPF) of 1.0" to 1.3" for Harrisburg. This guarantees that even a "sleet-heavy" outcome will likely result in at least 9–10 inches of dense, frozen mass.
Final Forecast Recommendation
Stick with the 11"–16" range as your baseline, but keep a close eye on Fredericksburg (KEZF). That station is your "Early Warning System"—if they are still snow at 8:00 AM, the HRRR's 18-inch solution is no longer just a possibility; it becomes the most likely outcome.





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This is amazing 

[2001kx]

23 minutes ago, Ruin said:

Hope the radar fills in more a little gap between the system 

Yeah it looks disorganized as of now..

[Mount Joy Snowman]

HRRR a skosh warmer through 12 compared to 18z but also higher on early totals, perhaps coming in a bit hot and heavy.  Let's see how she progresses. 

[AccuChris]

HRRR is like watching a heavy weight fight between dense cold air and strong WAA lol


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[Mount Joy Snowman]

Looking ever so slightly better through the late afternoon to early evening hours across Lancaster County.  Such a battle but cold air gets a couple more punches through compared to 18z.

[canderson]

Basically if rates are fairly heavy you stay snowy. When it gets light it flips. 
 

We went to Devon for dinner and it felt like the last night before Jesus returns. Wall to wall people celebrating life. 

[Mount Joy Snowman]

Map reflects a solid improvement for Lanc/York Counties.  Hard to overstate what a battle it is in the thermal department right over the southern tier.  Route 30 warzone.  As others have stated, nowcasting from here on out.  Let's go!

[AccuChris]

Long range HRRR is very much in line with the GFS/Euro blend


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[Blizzard of 93]

@psuhoffman just made a great post about the model situation for this storm.  

“So I’ve never seen this drastic of a split between the globals and American run CAMs at this range. What’s odd about this and gives me no past reference to draw on is typically when we see this kind of thing the euro and rgem/HRDPS kind of bridge the gap as those 3 are decent at seeing mid level warming. 
But they are all in the camp with the other globals (UK/Icon/gfs).  The impact is most drastic actually for Maryland. Around DC and south we’re talking maybe the difference between 4-5” and 6-8”. But for places NW of 95 in extreme NW VA up through central MD we’re talking the difference between 5-6” and 10-12”!   
The divergence seems simple. The globals along with the Canadian high res models have an intense WAA band over the area from 12z-18z that the American CAMs do not. That’s why they are warmer.  Less dynamic cooling to fight off the WAA at mid levels. Also less precip. That combo means 6” instead of 12” for places like Winchester-Frederick-westminster. 
What this comes down to imo is which camp is correct about the precip representation from 12-18z. Unfortunately I don’t have any great insight. Usually here is when I’d be saying “in this or that situation this is what happened” but I can’t remember a single case like this to draw upon. 
I guess I’m gonna ride with the euro camp. It would be hard to take the NAM and a bunch of experimental stuff over the highest verification tools we have. But on the other hand those CAMs were designed for this. When they score the euro a 30 mile shift in 800 mb temps and a meso scale precip band aren’t really going to impact those scores at all!  
Yes I just contradicted myself. If I had to make a forecast maybe I’d hedge and go in between even though that’s probably not the most likely outcome, one of these camps is going to win”

[canderson]

I plan to be a first shovel at 1 p.m.  if it flips after it’ll have snow on the grown, if all snow basically cut in half. Praying to baby Jesus it’s all snow and I get 12”. That’s my goal - a foot.