MAG5035

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.