MAG5035

Light snow has just gotten started here, a bit ahead of schedule.

Your welcome, and actually CTP has just updated their disco. They got all the good details in there haha. Also, they have a climo section for record snowfall.. which this is poised to break 2 day largest snowfalls for December in all the CTP climo stations (UNV, IPT, MDT).

That portion of the disco hasn't been updated since about 10 last night. However, overnight and early morning guidance (6z) have continued to support that notion of a 24+ axis somewhere between I-99 and I-81 northeastward toward the Poconos. Exactly where is likely going to eventually be determined by today's near term guidance as the event unfolds. Still trying to adjust to the fact that we're trying to pinpoint the highest totals within a nearly region wide foot plus in all guidance for us haha. I think CTP has a good handle with their current snow map. I do like that general area of Lewistown to Selinsgrove up to Williamsport for the best opportunity to get to two feet or perhaps beyond. For State College I'm thinking 14-18", but definitely a shot to get past 20 or so. Gonna depend how far back those CSI bands set up the first half of this evening, and to a lesser degree how well the storm accumulates rate and ratio wise during the WAA phase of precip today. If State College does get into the thick of it, I'd look at the 7 mountains region of US 322 between there and Lewistown for something ridiculous. Again, this is pinpointing where these excessive totals might pop up within the general 10-20" this whole region stands to see. Making a fairly safe call of 14-16" for the backyard (Altoona), it's weird saying that much is a "safe" call haha. They're sort of in the same boat as State College with perhaps the outside chance of seeing 20.

Way too early look at the 6z HRRR which extends out on the 0,6,12,and 18z runs seems to jive okay with things. For some obs here, it's a nice crisp 26ºF currently with some increasing clouds and a light easterly breeze.

How do you feel about good ole Williamsport being a snow chasing destination for this storm? Haha

Unless your already booked up in Williamsport, since your leaving early in the morning I'd have a good look at 0z and 6z guidance to make sure the swath of excessive snowfall is still going through there directly. A couple backup options might be State College, somewhere up US 15 between Harrisburg and Willamsport (Selinsgrove-ish) or Lewistown on the US 322 corridor that goes between Harrisburg and State College... although I think any of those options are looking pretty good at the moment haha. All those places have pretty good roads so I would imagine they'll be reasonable by Thursday evening since this is supposed to end by daybreak Thur. If they aren't, well then you probably picked the right place for your snow chase haha. CTP mentioned about CSI banding in their discussion, that's the kind of setup you could easily get thundersnow or certainly very intense snow rates out of. And lastly, I'm still on the fence with these Jan 2016-esque totals that persist on model guidance. Within what looks like pretty much an area wide 10-20", I certainly think at least a thinner stripe of 2'+ is possible anywhere between I-99/220 and I-81 depending on where these intense bands set up. These bands are likely to have better temps aloft in the snow growth layer to boost snow ratios being located in the central part of the state. A 30" is doable, but that would be one heck of an experience to get there since this looks like about a 15-16hr storm.

I honestly don't see much change from 12z to 18z or really anything major from model to model at 18z in terms of the surface track when comparing stuff. I'm not going to chase every random kink or secondary max in the isobars. Everyone's going to get a significant snowstorm. Where the best 700mb forcing resides is going to be where the top end snow totals are going to be found and the amount of warm advection aloft is going to determine what kind of mixing issues occur in the LSV, specifically below the turnpike. Model's aren't quite honed in on either yet, especially the mixing. The 18z GFS basically tracked the surface low pretty much the same the 12z as did the 12 vs 18z NAM. Now NAM has looked a bit southeast of the GFS but the NAM sends a lot of sleet (3k had 1-2"+ worth) into the LSV and the GFS basically has the surface low running a straight rain/snow line. The culprit for all of this is not at 850mb but at the 700mb level. There's a huge difference between the NAM and GFS on temps at that level. NAM GFS There was a compromise to be in had in the form of the earlier 12z Euro which is tracking similar to the GFS on the surface. That was borderline at 700mb but generally stayed below freezing at that level and at 850mb where it showed mix.. like indicating a briefer intrusion of the warm nose somewhere in between those levels (probably a more reasonable assumption.

High water mark of the mixing at this 42 hr frame. Mixing at 39 and 42 above mason-dixon. Everyone back over at hr 45. It's hard on these 3 hr maps to really tell whats going on QPF wise but it appears to me the mixing period might conincide with a slot (or lighter precip at least) working up into the LSV, which is certainly possible with how close the low gets before fading. Euros only putting out small sleet/ice numbers and then the backside sets back again as snow. It's still going to be a significant snowfall regardless. Hr 42 10:1 map

Yup I think it would be. 96 and 03 came the closest with 18"ish. Nov '95 was also a 15-18" type snowstorm in UNV. It would be the first one for me personally from an IMBY perspective since '94, which I was 6-8 years old in 92-94 so I don't really remember that golden age for big snowstorms in this corridor. Jan '96, Feb 03, and Feb '10 were all high teens storms (still great events though of course). Just missed the 20"+ by about 15-20 miles in 2016. Hard to do around here, I'll believe it when my homemade snowboard that tops out at 20" disappears tomorrow night lol.

With model's seemingly starting to zero on taking the surface low essentially to the Chesapeake Bay Bridge (the Baltimore one), it's pretty likely at least the southern parts of York/Lancaster have a period mid storm where they mix. I think it'd be mainly sleet north of the mason-dixon line but a low track that close is probably going to introduce p-type issues there for a couple hours. Once the low starts to make it's fade heading toward going under Long Island and New England I think anyone mixing in PA will promptly go back to snow.

<3

In other important details about this incoming barn burner, it has been named Gail.. haha. https://weather.com/safety/winter/news/2020-12-14-winter-storm-gail-noreaster-east-coast-snowstorm

Crushed.. this gets everybody here and even gives the Pittsburgh folks warning snow. It does nose mixing (primarily sleet) up into York/Lancaster and even up towards Harrisburg mid-storm. Using 10:1. Kuchera totals are 2' + in the AOO-UNV-IPT corridor.

GFS has really looked solid the last full cycle back to 0z last night. It's also tucking the low from SE VA just inside Chesapeake Bay thru the Delmarva now like the Euro has been doing, which has been solidifying our northern and NW folks into the better totals and keeping the Pittsburgh/SW PA folks in high end advisory (maybe low end warning) numbers.

Hmm it's still showing some surface reflection into the OH Valley on the models, so I don't know if it'd be a clear cut miller A if we're being technical. But with the coastal getting going early and tracking where it needs to for this area on pretty much all models now.. it might as well be one.

A system originating from the Gulf states developing a coastal low tracking up the coastline near or on the Delmarva into the teeth of a strong Canadian high are what C-PA snowstorms are made of.

Lol, I was using the 12k NAM since some of this event is still outside 60hrs. 3k NAM is definitely NOT acting up haha, geesh.

Yea, my bad. it's starting to pull the heavy snow swath back towards where general consensus of the other guidance has it. Seriously though, did anyone else with WeatherBell have a screwed up 18z NAM like I did?

Well looking at it with Weatherbell's map something was up with the model run itself on there. Def the current 18z run but it there was some of the precip shield that cut out on a couple frames, really weird.. and it's not totaling snow right either. Heres what it did hr 57 vs hr 63 frames for example 57: 63 So there's definitely something up there, I know the TT maps can really exaggerate snow totals near the mix areas but it was like looking at a completely different model run lol.

Eh not really, track did shift SE a bit coming up the coast but still a lot of mix in the LSV and it really shut off the precip fast once the low's gettin by us.

Yea there were definitely elevated ratios there and in that general band of the LSV that saw those 30+ totals. Jan 2016 was a colder system but if you have a good snow column with no real warm nose in it (enough to affect the snowflake structure) and any typical surface temps cold enough for snow to accumulate well... the thing that matters more for ratios is where in the column the lift is occurring and what the temperatures are at that particular layer. For this, the better ratios will probably be where the best lift is at the 700mb level (and somewhat above) and where 850mb temps don't flirt with 0ºC.

Yea this is where we have to be careful. It's definitely possible with this event in terms of having a widespread area of 6"+ like that. Again the big question for this subforum in particular is not really whether all of us see decent snow totals but where the swath of heavy to excessive snow is, and how expansive... with the secondary question being how much if any mixing gets into York/Lancaster counties. I tend to think any swath of widespread 14-18"+ amounts may be more focused than the broad swath the Euro is presenting, with the majority of the rest of us NW to 2001kx in Clearfield in the 6-12" range. Models are still kind of up in the air about that. Canadian is still the tightest of the bunch and has the excessive snow swath only really in the LSV from H-burg and SE out to Allentown and really hurts the folks back this way in JST/AOO/UNV taking away the bigger event and beyond in western PA. Canadian ensemble has the swath somewhere in between the GEFS and Euro EPS though. NAM is way NW with the mixing line and heavy snow swath (probably too much so). GFS does okay, its starting to hug the coast a bit more but still has a more outside track on approach. Euro is pretty far inside, actually inside the Chesapeake Bay across the Delmarva to Delaware Bay with it's low on the way up the coast. It's actually pretty much what the NAM did track wise, except the NAM was much warmer thermally.

The more elevation dependent HRRR ended up being correct over the other ambitious guidance this morning. Probably could call it a T here, but nothing measurable fell. Looks like it stuck from about 1800’ or so up. Looking NE Good thing we might just scrounge up a bit of snow Wednesday lol. Did anyone actually see much this morning?

Steadier precip has arrived, looks like a rain/snow mix currently. 37ºF

Euro's hanging the deform max in between I-99 and I-81 this run, everyone in here's crushed.