MAG5035

MJO has been a fairly big driver in the turnaround to warm the last several days and looks to potentially remain a factor as we get later into the month. You can see that it entered Phase 4/5 by Dec 22, right when the arctic blast crashed through us… and has spent the last week cycling 5 and 6. Now this teleconnection isn’t instantaneous, but when you consider how strongly correlated to eastern warmth 4-6 are during the winter months.. you can see why our cold snap was cut short when it could have lingered longer without this major reshuffle in the pattern. So we’re already into Phase 7 technically, which is a “better” phase… and the pattern responds as such after the Tuesday cutter as we get some Canadian ridging above and knock down the SE ridge.. allowing an attempt at perhaps a more favorable storm track and temps that could still be an issue.. but still doable for snow for us in the right setup. It seems the Jan 6-8 timeframe could present something either in the form of some kind of inverted trough feature with the lingering upper low from the midweek system or maybe a whole other system a couple days later. Hasn’t been much consistency yet on either feature. MJO forecasts going forward suggest an attempt at getting into phase 8 and maybe 1 and 2 depending on the forecast. I put up the Euro and ensembles for this post, which shows a sluggish move into 8 (GEFS similar) but the extended (monthly) Euro shows a more consise 8-1-2 run as we get from about mid month on. That would be ideal to help set up an eventual return of a widespread below average temp regime to the eastern US, something the ensembles seem to be introducing currently esp beyond D10. In the meantime, we maintain a half decent setup for undercutting storms with higher heights over Canada.. but the potential will get better in time temp wise if/when we get some better support in the Pacific realm (EPO). Right now we’re not really looking at true cold in the pattern initially even with a better looking storm track on our side of the country and a continued mostly -AO. That’s due to the low heights and suppressed jet in the northern Pac keeping an active pattern into the western states, not to mention the aforementioned above normal heights in Canada correlate to significantly above normal temps for that region as well. Once we build some western ridging and ideally reverse the EPO back to negative, we should tap back into a much colder air source. Whether or not the MJO does a full blown 8-1-2 run, I’m kind of glad the MJO has gotten this 4-5-6 run out of the way and didn’t stall in those phases in the process. As long as it stays out of there, we’ll have a chance to deliver a favorable pattern for cold and snow. And it appears barring any major changes the next couple weeks that we’ll likely stay out of it for at least most of January. Otherwise, you couple that 4-5-6 with the moderate Nina base state at any point in the next 1.5-2 months and it’ll be more of the kind of weather we’re seeing right now.

51ºF here, the first such day (50+) in the last 22 days. Definitely some melting but yard still maintaining pretty much full coverage in terms of the pack, for now.

Merry Christmas everyone! Temp has reached a balmy 15.1ºF, still a pretty stiff breeze. This arctic air mass has definitely been something else. TIme of the year (min sun angle) has a part in it but since the air mass arrived Friday Morning temperature trends have been completely non-diurnal. Christmas Eve here had a -3.5ºF low and a high of 10.8ºF, which was reached right at midnight last night. Mean temp yesterday was 2.5ºF, averaged from obs every min. Today had pretty steady temps with a low of 10.8 and high 15.3ºF. As mentioned yesterday, we spent about 18 hrs straight being below zero which covered max daytime heating hours Friday. And consecutive single digit temps ranged from about 1030am Fri til 1130pm last night (37 straight hours). That’s some pretty impressive stuff, it can get cold around here and obviously much colder in radiational cooling situations but you don’t see that kind of cold very often directly associated from the air mass. Temp/Dew/Apparent graph Dec 22 to Current

Low was -3.5ºF last night and just now getting above zero degrees. That made for an 18hr period that it was below zero here.. which is pretty impressive.

JST, which is at -8ºF currently, had a wind gust to 60mph at some point in the last hour. Current ob (about 10 min ago) is sustained wind of 35 and G44. Thats a -38ºF wind chill when applying just the sustained wind. I mean I can’t think of another arctic shot off the top of my head that combined actual temps of that caliber with such high winds.

PennDOT RWIS station on Cresson Summit on US 22 just west of Altoona. Max gust of 60mph, consistent gusting near 50mph. Ouch.

State of the snowpack as promised, you can also see it’s been windy here today with all the pine tree debris. Going outside to take this picture took my breath away.

Officially below zero now here, at -1.5ºF with a -10.7ºF dewpoint.

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.