MAG5035

Follow up on this part of my earlier post. All the regulars in here know if there’s snow showing anywhere on model guidance that Blizz is on it. And in the case of this potential event Fri/Sat, here’s multiple receipts courtesy of him… as far back as the 14th! Yea guidance has been inconsistent and all over the place, but this potential event/setup didn’t completely come out of nowhere.

What’s jumping out to me with the initial look into this is surface and 925mb (3000ft) are very cold in central/eastern PA on most guidance. The difference between the Euro and GFS camps right now look to be centered up a little higher at the 850mb (5000ft) level where the Euro is warmer, which lends to it’s more predominant freezing rain p-type vs the prolific pinger fest the GFS has in the central counties. On the other hand, the Euro never seems to portray sleet very well with its p-type algorithm. It certainly still looks supportive of a lot of sleet despite warmer 850 temps because of how cold surface and 925mb is. So as it looks right now, I would lean towards sleet being a more dominant p-type with the significant freezing rain threat in the Laurels. Then of course figuring out the front end snow threat as well. The eastern third of so of PA is definitely in play for a thump, will have to see if any of the central third can get some snow as well.

More often than not models don’t do well handling features with NAO blocking in the medium range, which isn’t necessarily anything new. So they’re now responding to what is looking to be a bit stronger of a -NAO block. Its high stakes with the changeability because our area is on the fringe between a surge of record warmth in the central US and still a decent source of cold air in Canada, which the -WPO (Bering Strait ridge) is providing despite the variable EPO and negative PNA. The northeastern US was never supposed to really warm up, at least for very long because of the -NAO holding off/muting the torch pressing from the central US, something I touched upon in a post a couple days ago. Now that we have a feature and high pressure suddenly lined up with plenty of cold available to bleed down, we have our setup for a mess instead of a day that looked like was heading for 55-60 a couple days ago. I know I did a double take yesterday when I saw that guidance went over to this. Funny thing is, this system has shown up in some fashion off and on in that 12/26-28 timeframe on deterministic guidance basically since it’s gotten within the range of it.

Maybe in western PA, cool air has a good chance of holding in the rest of the state east of the Alleghenies Christmas Day. GFS a bit cooler than the Euro (actually slightly below average in eastern PA), but even the Euro only has MDT getting into the low 40s or so. Even if it did bust 50 degrees the +5 to 10 departure that would make high-wise is pretty tame compared to where the real torch is centered. + Anomalies Christmas Day in the central plains are bananas, in the realm of 30-40 degrees above average. We may have a couple fairly warm days on or just after Christmas, but the -NAO blocking is likely going to keep us from being overrun with any kind of warmth like that. 12z GFS temps/anomalies

Somewhere in the ballpark of an inch of wind blown snow. There’s also been several snow squall warnings around as well with one currently stretching across I-99 from just north of Bellwood to Tyrone and extending over towards Lewistown The high wind warning worthy gusts in the actual warned counties may occur during the next several hours as near term guidance showing an enhancement of winds on and just east of the Allegheny Front centering on roughly the 7pm-midnight timeframe. Some HRRR images for 10pm Surface wind gusts (mph) 925mb winds (knots) 850mb winds (knots)

It hasn’t been crazy windy here, so far. Only have like a 33mph high gust on my station. But it has been snowy the last couple hours with some pretty robust upslope snows ongoing in the wake of the frontal passage. Have at least a half inch or snow on all non paved surfaces.Temp down to 25ºF. Official station high gusts around here so far have been 52 mph at KAOO and 56 mph at KJST.

Agreed, I know I’m not going to nitpick what constitutes a “torch period” regarding the weather from about yesterday thru the first half of tomorrow or so. Given how potent of a southerly flow this system has that is going to tracking well north of PA, it could definitely be warmer out ahead of it here. LSV might briefly climb into the high 50s prior to FROPA tomorrow morning before a brief but potent return to some below average temps later tomorrow. With that said, we do have an actual torch period setting up through at least the Christmas to New Year’s period… centered on the central US. Really about the only teleconnection we have going for us in this timeframe is a developing negative NAO.. which acts to keep significant warm anomalies at bay in the northeastern US. The degree of which is what modelling is back and forth about. I think in play here in Central PA are a couple of waves that may have enough cold in place to produce some kind of a wintry mix type scenario. But overall looking like more of a transient/brief cold enforcement vs the kind of persistent cold temps we had the first half of the month. I’m overall kind of pessimistic about this period, as I feel the mostly +EPO and now significantly -PNA are going to be a stronger teleconnection influence vs the -NAO/neutral AO. Keeps very cold anomalies bottled up in western Canada and storm track continues to be northern branch dominated with little southern stream action as evidenced here by a very dry southeastern US. GEFS v Euro EPS temp anomalies (10 day avg centered beginning of Christmas week to New Year’s Day)

2.2” was the total snowfall here. Some of the LES/upslope stuff starting to roll in here now. Temp down to 16ºF.

I can’t resist sharing this lol, 1pm Christmas Day GFS vs Euro 0z run tonight. Literally a 50 degree difference in temps.

As of midnight.

I’m a little over 1.5” here with still some more to go. Been pretty steady since this started around 4pm this afternoon but it’s largely been the pixie dust variety so I don’t really have as much to show as I probably could with it essentially snowing for the last 8-9 hours. Temps have started to fall steadily in the last hour or so, down to 24ºF from about 27ºF at midnight.

Passing an inch here with steady light to moderate. Roads covered and 29ºF. Next couple hours are going to make or break the event here I think in terms of whether I can score a solid advisory event. Some of the better enhanced banding over Pittsburgh should translate over this way in that timeframe. Downsloping hasn’t been too much of an issue so far here being right against the Allegheny Front. Should also note starting to see the enhancement of the precip in the Sus Valley as well on CTP and LWX radar.

Snow has started here, 32ºF.

Might as well throw some accums out since this event is pretty close to starting in western PA. This is going to be a pretty big event in the western mountains. The western ridgelines of the Laurels may near double digits just from the event itself with the upslope flow and cold column (high ratios). Still going to be that corridor of reduced accums in the Ridge and Valley, although this has looked somewhat better as this has gotten into the realm of the near term guidance. I think most everyone will see at least an inch. That narrow corridor between the Allegheny front and I-99 may manage low end advisory amounts. Along with the somewhat better carry-over where the downsloping occurs, near term has also looked better in the Sus Valley for the precip shield reorganizing as the system gets to the coast and the column/surface cools further. Ratios won’t be as high as the Laurels, but it’ll still be pretty decent (perhaps as good as 14-15:1). The best precip coincides roughly with the -8ºC 850mb isotherm as it tracks across PA. It wouldn’t take much more QPF to make for a low end warning event in the Sus Valley. Western PA Pittsburgh metro and surrounding: 4-6” Washington: 5-7” Butler/Indiana: 3-5” Seven Springs: 6-10” (+ additional with LES and upslope after) Central PA Johnstown/Somerset: 4-7” (+ additional with LES and upslope after) Clearfield: 2-4” Altoona: 2-3” Bedford/State College: 1-2” Huntingdon/Lewistown/Williamsport: An inch or so Sus Valley Selinsgrove: 1-2” Gettysburg: 2-3” Harrisburg area/Tamaqua: 2-4” York/Lancaster: 2-4” (possibility of some 5”+ amounts)

The HRRR is suggesting that right at the very beginning when it precip arrives into the LSV. I would think it would be brief if it happens. Surface starts above freezing but 850mb and 925mb level are plenty cold to start the event and cool further as the event progresses. I think this event should get the rest of the LSV solidly on the board in terms of first synoptic snowfall.

Here was latest extended run of the HRRR (12z) this morning The biggest thing to resolve in C-PA with this system is the extent of the snow shadow east of the Alleghenies. Pretty much all modelling shows this now to varying degrees basically in between the I-99/US220 corridor and the I-81 corridor. Models like the GFS or the 3k NAM don’t even give much snow to a large portions of the Sus Valley. The wave itself is fast moving and very weak with not a lot of moisture to work with. The mean flow in the low levels remains westerly, which is why you see such a pronounced downsloping shadow off the Alleghenies on modelling. So unfortunately I expect this feature to show up with likely a corridor of T-1” snows in the ridge and valley. How fast that precip shield reenhances as the weak system reaches to the coast will dictate how much of the Sus Valley can reach at least a low end advisory type snowfall. I think York/Lancaster probably does okay, not sure about the Harrisburg area (right now I’m thinking about an inch maybe two in that area). Obviously western PA doesn’t have to worry about the downsloping component and that coupled with this being plenty cold with pretty high ratios it should be a pretty nice event over there. Given the aforementioned low level westerly flow, that will act as an upslope component on the western leading ridges of the Laurels, which is why you see those higher warning totals show up there.

Thats quite a snow band, it’s actually reaching the whole way over through Lower Manhattan and Brooklyn in NYC where OKX has a special weather statement out for a dusting to an inch.

It’s even more pronounced on the other globals. Especially on the GFS, which doesn’t have a snowflake make it east of I-99. GFS is probably on the far end of that side of the spectrum (and a bit further south with the wave as well), but that shadow off the Alleghenies is probably going to be a thing with this setup. The wave isn’t all that strong and doesn’t have much moisture to work with. Most modeling doesn’t have a closed surface low until this hits the coast, which is why the second snow swath shows up in SE PA and the DC to NYC 95 corridor. Otherwise the wave is running on a westerly flow, which downslopes off the east side of the Alleghenies. The 0z NAM had a more pronounced shortwave as it passes under PA, which made that about the only model to not have the shadow. Other modelling tonight 3z NBM (National Blend of Models) vs NBM v5. The v5 is an updated version of the NBM being tested ahead of being deployed April 2026. 0z Euro

The EPO plays pretty big factor in this as well, surprised he doesn’t mention it. After it takes a major dip the rest of this week behind tomorrow’s system all ensembles have it reversing to a pretty positive regime by later next week getting into Christmas week, setting up the period where we may moderate. Ensembles do show the very persistent -WPO regime in a pretty classic representation of such with major ridging centered on the Bering Sea throughout. This helps establish cold continental source region of the airmass into Canada. In combo with a -EPO that’s a good recipe for dumping cold over most of the eastern 2/3s of the lower 48.. which is what we see coming up the next 6-10 days. EPO in its negative phase promotes more ridging into the west coast of the US up into Canada and Alaska, and a stronger jet/lower heights into the western US in its positive phase. It has high correlation to anomolous temps cold (negative) and warm (positive) in our neck of the woods. A split in the teleconnections with a -WPO/+EPO makes for a bit less certainty. If teleconnection forecasts are right with the switch to a solid +EPO we’ll have a good bit of Pac modified air injected into the pattern but also still plenty of cold in Canada. Another factor to pair with +EPO here is AO/NAO also being forecast to be positive, which implies lower heights nearer to the pole and a contraction of cold air press into the CONUS. So there is a pretty solid case for moderation here because while there is plenty of cold available in Canada this combo probably sets up a high zonal flow across the US. I don’t necessarily see us torching but I see it more as a detriment in terms of storm track (low track running north of PA) since we have had a northern branch dominated regime and next to no southern stream influence so far in the early going. It might still roughly reflect a P8 MJO regime in the temp department, but that alone doesn’t put the white gold on the ground. So we’ll see how that evolves, in the meantime we will continue to be cold for the next week or so with the opportunity for at least another light snow event or two, with the Saturday night/Sun wave showing the best promise. There won’t be much moisture associated but that particular wave will have pretty cold air set in place, and a couple of tenths of QPF could easily turn into a 2-5” type event.

Temps have fallen all the way back to 9ºF here so far tonight, with some more room to fall further with a 5ºF dewpoint. KBFD already has another below zero night (-4ºF) currently, which makes two of those within only the first 8 days of December there. Even being generally the coldest official station in PA that’s still pretty impressive.

I can’t believe no one’s made a winter thread yet, we’re 8 days into meteorological winter and we had a day last week where CONUS snow coverage for this time in December was the highest (45%) since 2005 plus our snow event last Tuesday and now the second snow event for VA going on today. So I’m going for it https://www.americanwx.com/bb/topic/62436-central-pa-winter-2526-discussion-and-obs/

We have a couple potential events this week. A potent shortwave traversing the Great Lakes Wednesday and another potential wave(s) over the weekend. The low on Wednesday passes north of PA, which will likely focus snow potential in northern PA and the Laurels with downsloping off of the mountains and probably surface temp issues. Another period of significant LES/upslope likely ensues in the aforementioned focus area of snow potential after the passage of the low. More pieces of energy along this fast northern branch dominated flow are in the pipeline behind this, with all major models at 12z today focusing more towards Sunday for a more notable wave traversing PA with a widespread snowfall. Much colder air looks to be in PA for this weekend vs Wednesday. Still some potential light snowfall Friday night as well showing on the Euro. All these waves will be enforcing a continued regime of much below normal temperatures.

Probably at least 4” up on Tussey Mountain (approx 10 miles south of State College), although not completely sure since i didn’t bring anything with me to measure. Right at the 3” mark at home, and similar here at camp off the mountain. Almost at the end of the precip, definitely a nice morning overall. Now to get a system that does this for another 18 hours or so haha.

Already looks to be about 1.5” here and snowing pretty good. I’m at hunting camp over in Spruce Creek (NW Huntingdon Co). Looks similar at home, temp is 28ºF.

Overviewing all the model/ensemble stuff the last few runs I would think most if not all the subforum is looking good for the first widespread synoptic snowfall of the early winter season. I’m not really concerned about any P-type issues except for the LSV near the MD line, and even there I think there’s a good chance of advisory type snowfall or even a mostly snow event presuming we don’t trend the surface low NW much in the next 36 hrs. Think the ceiling in our area is likely to be 5-6” but mostly a 3-5” type event. Main issues I see to sort out at the moment is axis and width of the swath of heaviest snowfall. The regular Euro suite has been a bit more disjointed upstream developing the shield of precip. It seems to be the most progressive of the major stuff to include the GFS and Canadian suites, as well as the AI Euro. This makes for a late blossom of the precip shield over the majority of C-PA and a more focused swath as the coastal low deepens and moves NE. Basically everyone still sees snow but it’s a lot more 1-2” or so with a tighter swath of 3-5” type amounts… which is the furthest SE with that getting a couple inches all the way into DC. It’s reflective in the associated ensembles too. Might as well show them all. 0z GEFS vs Euro EPS 24hr probs of 3”+ 0z Canadian ensemble vs Euro AI ensemble for 24hr 3”+ probs, actually a pretty good match on swath axis The other end of the spectrum is the 3 and 12km NAM being the furthest NW, most wound up solution (no surprise) still as of 6z this morning. I’m sure thats the type of solution the MU guy is envisioning as the end game of what this system does in terms of the boundary being north. Which is certainly possible but I don’t see the amp in the pattern to bend this up in a Chesapeake Bay to NYC to Southern New England trajectory as deep as it has the low developing. And honestly that’s about the only kind of track I would entertain detrimental p-type issues reaching far up into southern PA and the Sus Valley. Otherwise I think this pattern setup we’re in is plenty cold enough to overcome early season climo. Yea the ridge axis is just off the Pacific Coast, but the PV is also anchored over Hudson Bay. Look at the 500mb anomalies for storm time. The only detriment of a +NAO in this setup would be a progessive pattern.