MAG5035

So far I'm seeing the same general thing as last night. GFS most southeast with it's heaviest snow axis and limits NW extent on 6"+ and CMC simultaneously with good extent in the subforum but it's axis of downright excessive snows cutting from York/Lancaster counties to Allentown (a bit NW of the GFS heavy swath). The good thing for us is we're essentially boiled down to where the excessive snow (12-18+ type stuff) band is going to be within what should be a subforum wide warning event (I expect warning criteria for 2001kx and wsptwx too) and perhaps some mixing issues for a time mid-storm near the LSV MD border. You should see the discrepancy with the GFS/GEFS vs the other globals over in southern New England.

On tomorrow's event, been watching the HRRR. It's been having more p-type issues especially in the Lower Sus Valley but even in the south-central counties back near the I-99 corridor. Could end up being even more elevational. I know surface temps have dropped off in a few spots where it cleared a bit but mesoanalysis showing 925mb temps aloft lagging in the south and HRRR has trouble getting them to 0ºC in the LSV during the event tomorrow morning. Something to consider for this event in the short term.

Yea GFS has had real estate between the coastline and the low center. Most other guidance has had that low inside the Chesapeake and Delaware Bay before it starts the fade under LI. I tend to lean towards the inside guidance. SST's are on fire anomaly wise and our cold air mass, while plenty cold for this... is not overly frigid. Would suggest the boundary this runs on will be right along the coast.

A little early for Mt Holly to hoist watches IMO, esp on the other side of I-95. They better hope the NAM's not right lol. Tomorrow afternoon will probably be watch time for CTP once tomorrow's wave is mostly out of the way and the 12z suite is out.

Hopefully I'll get to worry about that Thursday lol.

No idea what to expect here out of tomorrow but I’d consider a quick 1-2” a win. Snowboard has been deployed in the yard. I handmade this thing out of some misc scrap wood around my shop room last winter and never got to use it.

Yea we do need to start addressing this thing tomorrow lol. I think there's more uncertainty with that than Wednesday's event, which could be problematic because the timing of this is right at morning rush tomorrow. That combined with being the season's first chance at widespread snow is likely why they're pulling trigger on advisories for a general 1-2" in the LSV counties. There could be a ribbon of snow that doubles up on that if some of these amped meso models have their way. CTP discussion references good lift in the DGZ, which will ramp ratios. Limiting factor at least in the initial stages of the precip arriving probably will be B-layer temps probably being a bit warm. Precip may start as rain in the LSV. If the rates are there, look out once stuff starts accumulating.

Early looks at the 12z Euro ensemble, I've used products that separate tomorrow's event out. 48hr snowfall mean 12z vs 6z: 24hr snowfall probability of >6" 24 hr snowfall probability of >12" No probs were generated on the >18" and >24". No matter though, that's about as strong of a significant snow signal as you'll get out of the ensemble guidance.

The setup is such that Pittsburgh would do well with a miller B type scenario. The problem is the Ohio Valley low isn't very strong and we're transferring to the coast pretty early, making the bulk of the precip shield associated mainly with the coastal low. You hold that Ohio Valley low just a bit longer and stronger and you can likely get a slightly better easterly fetch into western PA to the Ohio Valley and perhaps maintain a better precip shield across western PA. I don't think this region is in play for what's looking like a swath of excessive totals somewhere further east BUT I do think low end warning totals can be achieved if the more amplified solutions have their way. We'll need the meso models to get more into range to see if that idea has any legs. For now though, I have pretty decent confidence with Pittsburgh metro and surrounding seeing at least a decent higher end advisory event by the end of this. I think the GFS is just a bit too tight and SE with it's swath. 12z Euro coming in a tad SE with it's heavy swath and appeared a bit weaker on the Ohio Valley side of things (def NOT on the coastal end), but maintains the advisory totals over the area.

Compared to the 0z the 12z Euro looks like it shifted the axis and the heart of that deform band SE a tad to reside right up I-81(0z swath of excessive was more between I-81 and 99 corridors. Still warning totals for all the subforum regulars and semi-regulars.

12z GEFS 24 hr 6"+ snow probs vs the 6z. Edit to add 12z vs 0z Canadian ensemble comparison for 24hr 6"+ snowfall probs:

2/5 definitely did, I still remember the CTP disco at about this range saying something like "maybe 3 or 4 inches for the counties along the turnpike.

Yup, that December 92 nor'easter pretty much started that portion of the mid-90s where the central counties were the place to be for these big coastals (Dec '92, Mar '93, Mar '94, Jan '96). With December 11-12. 1992, the crazy part about UNV's 18" was the fact that precip turned to rain in the middle part of the storm there (LSV had some decent snow but a lot of rain), while SW of there in AOO and into the Laurels stayed all snow and there was a 36" total in Somerset County. We definitely will have a better airmass in place for this one, however the 500mb feature was much more pronounced on Dec '92 (closed 500mb low). There's a whole bunch of youtube videos of TWC during that storm that I found last winter. Jeff Morrow reporting in Breezewood getting blasted with snow. These videos def helped last winter lol. https://www.youtube.com/watch?v=R-ueyO15a2o&t=31s

Haha well that's good to hear, I almost wanted to retroactively give myself a weenie tag on that post I made early this morning. There is definitely differences between this prospective event and that one and the excessive swath is not going to be placed the same (likely NW of the big cities) and probably not as widespread. I was commenting mainly on the u wind (easterly fetch) component. Big time u wind anomalies are a hallmark of a big Mid-Atl/NE snow event.

I dunno, looks more like a C-PA forum special lol. Euro places ground zero of the deform up between I-99 and I-81 up through IPT into NE PA. Until this gets into short range, I'm only posting 10:1 maps if I throw up a snow map. Just trying to keep the top end capped while addressing the storm til we get into short range. But with that said, gotta acknowledge that models are dialed in to an excessive event right now... with every major op (CMC/EURO/GFS) having a 20"+ swath. The key is WHERE that excessive swath is located, which models haven't really nailed down yet. These Kuchera maps are nuts. IPT for example is 33.8" on 2.09" of QPF. That's a 16:1 ratio, which is probably doable wherever that intense deform sets up given pretty decent column temps where there's going to be monster 700mb lift, and there's a big swath of these accums in central to NE PA. Even a more standard 12-13:1 ratio is in excess of 2 ft. The knock on Kuchera is it calculates ratio solely on temperature by simply calculating a ratio from the warmest part of the lower 500mb of the column. It doesn't factor snow growth characteristics, omega, etc like BUFKIT data or the Cobb method would show. I have access to a Cobb map from the Euro and it's just as crazy amount wise but a touch east with pretty much I-81as the axis line, likely matching up where the best lift actually is. Actually gives Harrisburg an even bigger total than the Kuchera. Crazy numbers these models are putting out. Lastly here's the Euro's U wind anomaly at 850 mb at 102hrs (height of the event). Basically this is an indication of the strength of the easterly fetch. A highly anomalous easterly flow is a hallmark of the big ones. A -4 to -6 anomaly is through the roof... that's Feb 5-6, 2010 level stuff in terms of that indicator... key phrase being "in terms of that indicator". Should note GFS has similar anomalous flow, just not penetrating into PA as much as the Euro, which is why it's heavy swath further southeast.

On a run to run comparison, there was a big difference in heavier snowfall placement outside of the LSV (NW of H-burg into central/northern PA) with the 0z GFS vs 18z. Not really reacting too much to it as it's one run on one model, just pointing out the difference. As a whole, this is becoming more of a figuring out how much of the subforum is going to get slammed with a big snowstorm type thing. The big forecast challenge to me right now is the actual central part of the state and how much of it gets into the more excessive snowfall. I just feel even if we had the more inside scenario that gets mixing into York/Lancaster, it would be a transient issue that goes back to snow as the low deepens and moves up the coast.

Hmm, well at least on the WeatherBell products it appears the op data for the GFS and Euro is 0.25º and 0.1º respectively while their ensembles are both at 0.5º resolution. Without getting into a whole thing on GIS/mapping/degrees to meters conversion, the short answer would be yea the ensembles are run at a lower resolution (higher degree number). The high res Euro at 0.1º would be a bigger resolution difference vs it's ensemble. So I guess it could be implied that the lower resolution could flatten mesoscale features and thermal boundaries a bit and that difference could show with coastal low development, especially with how warm the water is off the eastern seaboard. Also, ensembles aren't going to see CAD as well as an op or especially a meso model for that same general reasoning. The higher resolution of the ops might be promoting a more explosive coastal response (and also closer to the coastline) just simply on the premise of modeling a sharper clash of warm vs cold. Given the +SST anomalies present on the eastern seaboard and a fairly respectable cold air air mass being supplied by the Canadian high, it may be wise to lean that direction with trying to blend guidance. Ultimately, I'm not sure how much the resolution difference actually plays in the grand scheme of things, as an ensemble is made of individual members that have their own specific conditionals to form a mean within a range of possible outcomes, which pretty much can have a similar effect as lower resolution flattening features out. Thing with ensembles is we're typically looking at them to get a handle on overall larger scale things with these events (QPF fields, pressure/height fields, accumulation probabilities, etc).. especially at this middle range where we don't have our short range or meso models in range quite yet.

I was going to address ENSO and the pattern going forward in a post at some point and then all heck went loose with what were looking at this coming week. So far, I haven't seen any sustained signs of an imminent weakening of the Nina. Daily SOI values and 30 day average SOI has been firmly positive (positive indicates Nina state) and SST's have been relatively steady. ENSO 3.4 has warmed a tad in last weeks update but still -1.1ºC (moderate) and the SON three month average came in at -1.2ºC. Three month averages are lagged, so when December is over and the OND average can be tallied, it's likely on track for a similar value to the SON average. Obviously, this is something to consider and watch evolve as we work through Jan. Right now though, the big driver of this snowy week that appears to be incoming is the development of a solid negative AO/NAO regime. This is a great time for this to develop as we're early in the winter and we don't have the fully mature mid-winter pattern where the Nina can rear it's ugly side at times. And of course, good blocking in that realm is a good counter to an active Pac jet (+EPO). If we can hang onto the -NAO/AO for awhile and keep the MJO at bay (out of any higher magnitude phase 4-6), we can take an occasionally imperfect but workable pattern thru the holidays to the New Year. But we shall worry about that after Thursday or so.

It was a concern I initially had, mainly because of timing and getting the systems too close together was my worry. As this has evolved the last couple days it doesn't appear to be as much of an issue, especially on the Euro. That has generally been the most aggressive model with northern extent on this first event and it's been subsequently pounding the Mid-Atl/NE with the main system regardless.

I've been away today and haven't had much time to scrutinize models too much, but vs the 18z NAM this first event is way more robust on the 0z. 0z on the left, 18z right

We’re definitely looking good at the moment, I’ve noticed the globals are starting to solidify the NW extent of the precip shield which is a good sign for getting west central PA and the Pittsburgh folks more involved. The Canadian op still seems the most SE with the axis of heaviest snow, but looks like the CMC ensemble align a bit more toward the GFS/Euro. Euro is def the most amped, pretty much representing a nearly best case scenario for most of our region save for perhaps a period of p-type issues in York/Lancaster. A simple blend of everything puts most of C-PA and all of the Sus Valley in a pretty good place. All of that for Wed/Thurs and the GFS/GEFS/CMC ensemble are showing more support for the Euro’s more robust initial wave and lighter snowfall potential in at least the southern tier of the state Monday.

Man I just looked at the Euro and almost fainted lol.

I'm going to wait a couple days to see where this goes before I start making comparisons, but I got a couple in mind.

The Ohio Valley low is going to be important for you and the western part of the state from the Laurel's west. The Euro had the stronger low I was posting about and it responded by getting better precip into western PA.

Well Euro is, snowy lol. What a hit on the eastern 2/3s of the state. Some snowmaps, these are 10:1 maps and i'm using 24 hr snowfall to separate the two potential events. This is Monday's wave, as Euro continues to support a snow event with that system: This is Wednesday/Thurs: