MAG5035

Yea that’s the feature that the likes of JB have been calling the “rear guard action” trying to drum up an east coast snow as the pattern shifts and the increasing heights/warm up presses into the Northeast as the EPO flips. There is in fact a half decent 500mb shortwave in that flow dropping down while we’re still in the very late stages of hanging on to the overall eastern CONUS trough, but feature looks postively tilted and stays unphased/progressive. I mean it’s too bad the western pattern will be shifting at that point instead of holding/building a ridge allowing better amplification because boy there would have been a big time phasing opportunity with that. But as it is, I don’t think it’ll be anything big BUT I could get on board with enough amp to generate an area of light WAA snows in PA that the models may eventually see better in the shorter range the next couple days. It would be warmer than this weekend of course but still fairly cold (def below avg) at that point as well. Even if it ends up being nothing or not much, it probably buys us an extra day or so of colder weather before the more significant warming trend.

Certainly the Laurel’s are heading that way for a -10 reading. There’s already a couple Mesowest stations near the 7 Springs resort that are -7ºF. I originally thought the HRRR was too cold but it’s actually looking pretty close with its temps so far. The other 12z models seem to be running about 3-5 degrees too warm in western PA at this point of the day, so that will be interesting to see. The 18z HRRR gets JST down to -13ºF tonight and gets a good portion of the LSV at least a touch below zero. NWS grids have -7ºF here for a low tonight now. It’s a legitimate dangerous situation with the wind chills. Normally temps this low come via a combo of calm air, radiational cooling, and snowpack. These temps are coming with 45-55 mph wind gusts.

I think it’s amazing that KPIT (Pittsburgh International) is -4ºF in the middle of the afternoon on Dec 23rd. I’m about to go below zero here. 0.1ºF lol.

Might need to cycle the AC to take the edge off lol.

A somewhat brisk 4.3ºF currently lol. So far peak wind gust measured has been 37 mph. Wasn’t much snow with the front, maybe a dusting. There is some light snow blowing around right now. Find the FROPA: Some other noteworthy things… I bottomed out at 984mb at the time of the front passage and the temp for the whole event yesterday never got above 33.4ºF at any point despite the monsoon last night. I’m pretty sure Altoona set both its daily rainfall (CTP noted 1.48” as a new daily max in its climo section ) and possibly daily snowfall record as well. Our local TV met said Altoona measured 5.2” besting the daily record of 3” set in 1926. Not sure sure what part of town that was, I didn’t have quite that much here (3.7”). CTP’s PNS yesterday did have several 5-6” amounts reported, esp towards UNV.

Probably unpopular opinion but.. I would rather have what’s coming tomorrow over this currently torrential rain and 33 degrees into a waterlogged snowpack. Is this what it’s like doing winter in the 95 corridor? Lol

No problem haha, I was looking to see if you meant the NAM or the GFS when you said that. At any rate even just a half inch to an inch with the rapid temp drops and winds is going to need to be seriously considered for flash freezes and issues on the interstates if one is travelling tomorrow morning. I think CTP probably should have hung on to advisories back here this evening for freezing rain. Lot of accidents and 911 chatter of iced up roads, especially on the roads going up the Allegheny Front…but some of the other local mountain roads as well. Temp here at home is just a hair above freezing at 33ºF. Edit to add, I do have some refreezing of my driveway going on despite salting it earlier.

Is the 18z Euro even out yet? I don’t see any guidance suggesting that at the moment.

Moderate rain and 32.5ºF, I got drenched finishing up snow blowing and shoveling. Here was the first tracks snow pic from a little while ago. I’ll have a follow up tomorrow morning on the pack after the Day After Tomorrow promptly arrives at 12z.

Precip has switched to light rain here, temp still just shy of 32ºF. Gonna call 3.7” as the snow total. C’mon dry slot haha.

The changeover is trying, under these yellows and oranges in the radar currently and had fast falling rimed fatties and probably some pingers in there too… now going back to heavier snow again. Temp back down below freezing (31.6ºF).

Still hanging onto light snow here, even as surface temps have creeped up to about 33ºF for now. Waves of snow have been sporadic the last couple hours so haven’t added much (just measured 3.6”). Eyeing a heavier band coming up from Bedford and a look at the 511 cams there (and at Breezewood) is showing it snowing all the way down to there yet and actually starting to cave the roads a bit again there. So will see what happens, the HRRR hangs on to snow and/or mixed through about 4-5pm here now.. and the more QPF that ends up frozen the better. Was glad to see that some of the LSV overachieved this morning and some of the colder solutions had some merit for a change. I thought Harrisburg could get 1-2” when I posted very early this morning, so nice to see some overachieving.

A nice burst of snow currently. Up to 3.4” here so far and 30.6ºF temp.

Early obs, temp just shy of 28ºF with 24ºF dewpoint. That’s up a couple degrees from being down as low as 26ºF earlier in the evening. CTP has expanded the winter weather advisory to the west bank of the Susquehanna (for 1-3” in the new counties), and also hoisted high wind watches in the NW and Laurels zones + Bedford/Blair in the I-99 corridor for 50-60 mph gusts and expanded the wind chill watch off the Laurels to also include Southern Centre (UNV), Blair (AOO), Huntingdon and Fulton counties. Like I said earlier, I anticipate wind chill advisories to be eventually hoisted for the rest of the area. Gonna be a wild 48hrs of observing here. Advisory for 2-4”, Wind chill watch for down to -30ºF wind chills, and high wind watch for 50-60mph gusts. I don’t recall seeing wind chill headlines like that here even during the cold shots of 13/14 and 14/15. The watch portion in the Laurels is for -35ºF chills.

Switching gears to the post front phase of this storm, really concerned about the combo of the cold and wind. I mentioned this earlier today but I’m going to illustrate. With the position of the very deep low, the westerly flow transports the arctic air from the north-central states underneath the lakes, meaning the unfrozen lakes aren’t going to modify the air via a NW flow like if this had been say.. a major coastal low lifting up the coast. It obviously does no good for much snow anywhere in C-PA once past whatever ends up right behind the actual front and maybe some lighter upslope type stuff in the Laurels. It sure will for western NY though, where BUF south probably sees x number of feet of snow again to go with their 40-60mph winds. At any rate, I really don’t think this is a situation where the cold “modifies” as it gets closer to the time it arrives. On the contrary, I think this is a situation that may be underestimated a bit. I used the 3k NAM for illustration, which is plenty cold showing temps getting below zero in the Laurels/NW PA. That’s also not the coldest frame as by 12z Sat, KAOO and UNV are also below zero with MDT around 5 or so. That’s where the wind has to be considered. I’m still not sure LSV sees crazy winds from this but you combine those temps with even 35-45mph gusts and you easily have wind chill advisory criteria in the whole Sus Valley. Here’s the 3k’s wind chills at 12z Sat morning: And since I mentioned about my worry that the HRRR might be too cold with the front end precip tomorrow, I might as well also mention that the last full HRRR run back at 0z was much colder than even this 3k NAM, having JST at -11ºF, -8 & -6 at AOO and UNV respectively and near 0 temps all the way to H-burg at the end of its range which is only 0z Sat. That is while having 50-60 mph wind gusts in the Laurels/immediately adjacent central with 35-40mph elsewhere at that point. So with all that, wind chills are practically off the charts for this region (nearly -40ºF in the Laurels) and -15 to -20ºF in MDT. I’d say thats probably a bit over the top, but either way I still believe the wind chill watch areas should go to warnings pretty easily, with the rest of the area seeing advisories. To put things simply, Friday night into the first half of Christmas Eve is going to be brutal until the wind starts settling down.

Hard to argue with a pretty decent model consensus getting notable accumulating snow pretty far into the Sus Valley, although I’ve been working on trying to be more cautious with these type of situations there this season after learning the hard way the last couple seasons. I’m still leery southeast of I-81. Comparison of the high res short range guidance shows some differences. HRRR has a much colder column, allowing the widespread snowfall as far into the Sus Valley as it goes. The 3k NAM (not the coarser 12k NAM) definitely isn’t as enthused, and looks pretty close to what CTP has out for a snowmap right now, not showing much at all in the LSV . That particular model erodes 850mb much faster in the Sus Valley and keeps most accumulating snow even out of Harrisburg. Adding to that, here’s what the 0z run of SPC’s HREF has, which looks similar to the 3k NAM. So just keeping things in perspective a bit, showing there are some high res short range things that don’t show the explosion of snow in the Sus Valley. I tend to think reality lies somewhere in between, as there should be enough cold to start things as snow in a good portion of the Sus Valley especially if precip gets here in a timely fashion and there are good rates. Top end accums are another thing to get sorted out. A lot of the short range and global guidance have no problem getting high end advisory amounts, with some full blown WSW type amounts in the interior south central counties. Still trying to figure whether I would want to pull the trigger on believing that or not. I do think the current advisory counties should be bumped up from their 1-3” to at least 2-4” with some scattered 5”.. and perhaps getting the 1” line to I-83 with Harrisburg maybe 1-2”. That would be my “safe” call with this. My worry is the HRRR is too cold.. and some of the short range stuff was a couple degrees too cold with the last event. I’m also not completely ruling out the colder, snowier HRRR type solution either.

The Pac influence this month definitely played a hand in delaying/muting the arrival of cold by at least a week or so in the first half of the month in the form of some troughing in the western states (-PNA) and also a small period of +EPO which has since flipped negative. It is finally in the last few days since last Thursday’s event that we have settled into a colder regime. Originally, an actual worry of mine going into this period we had of significant -NAO/AO was watching something big go south/east of us and snow on the Mid-Atlantic. If we would’ve had a more traditional big western ridge, that reality might have happened, or perhaps something in between. Teleconnections are just indexes, and the positioning of the features that drive whether those indexes are positive/negative/etc are not always completely ideal for what we want. Case in point with this coming system.. western ridge is positioned just a bit too far west. Now speaking about this particular cold shot, I agree in terms of longevity. The EPO is in the process of flipping back to positive over Christmas weekend, and appears to remain pretty positive next week and perhaps beyond for a time. That will shut off the arctic air source region and allow our weather to rapidly modify back to at least average temps. In the meantime however.. from about Friday night-Sunday night, this is going to be a major shot of cold and one of the coldest Christmas holidays in years. The combo of the temp and the winds behind this really deep low pressure are going to make for some dangerous wind chills. Pretty much all models are supportive of wind chill warning type apparent temps in the Laurels and north central mountains. The rest of CTP’s area will likely end up with wind chill advisories. The other thing about this system is since the deep low tracks through and north of the Lakes, the westerly flow pulls the arctic air directly from the North-Central under the lakes through the Ohio Valley to us. A NW flow over the unfrozen lakes would have modified the air some. The drawback there of course is that there won’t be much in the way of LES in the western parts of CTP as the W/WSW flow will target W NY and far NW PA once again for significant lake snows.

Sleet was the dominant precip type here on this side of the Laurel’s from that event. I had a fresh 0.7” of snow early Sunday morning from some upslope but otherwise all this on the ground is hard pack pingers. I guess that’s one way to ensure a white Christmas.

Models are narrowing the corridor for potential frozen on the front end, keeping it in the interior counties for the most part. Still a chance for the LSV to see some mixed depending on timing (faster) but it does appear that the best chance of anything accumulating stays west of the Sus river and likely closer to the I-99 corridor. Way too early look at the NAM…which has most of the front end phase in it’s range now is unimpressed thermally, with maybe a little bit of ice but not much in the way of any frozen anywhere. Will have to see how that evolves, one thing that occurred in the last event noted by CTP during the storm was models were a couple degrees too cold aloft, delaying the changover to snow that was supposed to occur for that. Different situation here, but a detail like that is something that could be the difference between a few inches of snow vs some mix and icing where models have been showing the corridor of snow. Either way, all of C-PA warms and any mix turns to rain ahead of the approaching rapidly deepening low and associated frontal boundary. It looks like the Sus Valley touches the 50s Thurs night into Fri morning with the rest of central and northern generally in the high 30s-low 40s. Frontal passage timing about late morning west to the mid-later afternoon east on Friday. Snow behind the front is still a big question mark of course. We’re probably going to have to wait for 3k NAM and HRRR time to really get a handle on that. Euro is really not printing much snow accums at all despite looking okay on the conditional maps. GFS puts out a couple inches of snow in the Sus Valley. Since this has really turned into straight up lakes cutter event with no secondary coastal influence, I do kind of worry about the downslope component drying out the precip behind the front, especially the in the southern parts of the Sus Valley. Plus the GFS has seemed to have a knack for being overzealous on digital LSV snow as of late. I don’t have any problem seeing those types of accums in the western half of PA or the Laurels but it’s a big question mark from the ridge and valley part of PA eastward. I will say this, considering the very rapid temp drops behind the front and gusty winds, ANY kind of snowfall be it a dusting or whatever could quickly create hazardous conditions. And being this occurs on Friday afternoon/evening of Dec 23rd, I think travelers probably should be mindful of that. Lastly I think most of the area probably see winds of the advisory variety with and behind the front (and perhaps some breezy weather in the Sus Valley beforehand). Outside of potentially the Laurels, I don’t think we’ll see any prolific high wind warning type winds that one would think you’d see with a deep storm of this nature. Reason being is i think the more western track of the low may take the best pressure rises through Ohio, western PA and western NY. It will still be quite windy either way with low wind chills, especially Fri Night and Christmas Eve.

Overnight model runs had actually bumped east some in the case of the GFS and Canadian, both having Apps runner solutions right through PA. Euro maintained its deep low to the Lakes and new 6z GFS has went back that way as well. An Apps runner doesn’t really suit us much better and in fact would probably slot us from anything related to the frontal passage/back end (esp LSV). What everything does have at this point is snow/mixed associated with the initial wave that develops on Thursday. This feature will have high support via 1035-1040ish high in Quebec, which will be retreating but would likely be enough for a period of accumulating snow/ice over a good portion of C-PA. Interior counties would be favored, but most or all of the LSV could get it too. The Euro continues to be the best looking model with the anafrontal feature associated with the frontal passage. I get that those scenarios are a hard thing to turn to real snow on the ground, especially in the LSV but this is one of those scenarios that should deliver at least a couple hours of snowfall behind the front. Modeled temps in H-burg (via Euro) go from 41 at 15z Friday to 26ºF at 18z and well into the teens by dark. The cold isn’t going to be screwing around. So I think there’s a decent chance of picking up an inch or two at least. Then there’s the whole flash freeze part of that as well. Still lots to sort out with that system as a whole. Can this main shortwave still end back up getting to the coast or coastal plain below our latitude? I doubt it at this point but not going to completely rule that out. Right now this looks like a pretty significant snowstorm for the Ohio Valley folks. Didn’t have time yesterday but wanted to touch on the pattern after this major weather system gets through. Christmas is going to be very cold for sure, and it will remain fairly cold for at least the first half of the following week between Christmas and New Years. Unfortunately, I see the pattern moderating for us and well a big portion of the CONUS before New Years. We neutralize but don’t lose the -NAO/AO but models all prog a major swing of the notably -EPO at present to an equally notable positive EPO by Christmas and especially later that week. Models have also been showing signs of moving the MJO through 4-5-6 during that week (likely not a coincidence with regards to the EPO going +). Given the NAO/AO still staying somewhat negative and the PNA actually being positive, we might keep a mean trough over the eastern US but the +EPO changes the source region of air to a more Pacific origin. So we might not torch…but it’s definitely going to warm up. I think the good thing about this is it appears that we could set up the MJO to be in favorable phases getting into January and as long as any pattern doesn’t bog down in 4-5-6, we’ll have chances.

Well something had to give with this, during the 0z suite last night we had the GFS low in Cape Hatteras while the Euro/CMC had it in Michigan. Of course the GFS joins the party today cutting what looks like is going to be quite a strong storm. As was mentioned, western ridge axis is being progged too far west to allow for the coastal solution. Barring any wholesale changes back the other way, I see two opportunities for frozen with this whole thing. Up front, where the GFS/Euro have been developing this wave on the coast in front of the main vigorous shortwave that becomes the big storm bringing precip into C-PA. This looked more like the Thur/Thur night timeframe. There will be decent high pressure (retreating) to the N and NE so anything associated with that may start as frozen, especially interior counties. Unfortunately with how things are being progged now with all 3 major models (with ensemble support), the vigorous shortwave digs and head towards the Lakes, which will draw up warmer air for a brief time (likely for about 12 hrs or so) sometime from Thur night into Friday. The second opportunity comes after the frontal passage, which looks like an anafrontal type scenario… something that could deliver snowfall for several hours behind the front. The cold air associated with this system will mean business and there looks to be rapid temp drops behind the front. Whatever gets on the ground from that will definitely be there come Christmas morning.

As far as event totals, I had about 1.7” of total frozen…basically 1.6” of sleet and a skiff of wet snow on top. Ice accums were negligible after it touched above freezing with surface temps but I think I had roughly a tenth of so of that this morning. The lull in the precip this afternoon definitely affected the overall outcome by coming to this area at a time when precip was getting ready to turn to snow and/or reach prolific pinger event status. The secondary batch mostly went just east of here. The result is a bit of a bust, but that much sleet is still a good bit to deal with. And it will have staying power with a cool forecast from here on til whatever happens near Christmas

We have flipped to snow here, steady temp at 33°.

In a lull in the precip currently, hopefully can get some regen of the precip shield back this way this afternoon. Something the HRRR continues to advertise later this afternoon (after about 19-20z) showing a renewed surge of precip (which should be mostly snow with the cooling aloft) into the central counties likely associated with the deepening of the coastal low. That’s going to play big on what the eventual snow totals end up being in the AOO-UNV-IPT corridor. CTP had already backed off some on totals due to models starting a couple degrees too cold with this initial phase of the precip shield. What’s also likely to happen as the low tracks across the Chesapeake into the Delmarva this afternoon/eve is that will eventually push the R/S line near or more likely above Harrisburg in the Sus Valley, so the next few hours is likely the time to put something on the ground for the LSV’ers that are seeing frozen precip.

Still pinging away here, my temp has actually creeped up to 32.7ºF. There’s over 1.5” of all sleet on the ground. Good to see some of you guys starting to see the snow changeover.