MAG5035

Frontal passage has occurred here, pretty decent gusty winds. Temp only got to about 41 or so during this whole thing today (about an hour or so ago) and it's back down to 38 already. Frozen precip shouldn't be too far off.

It seems like the most significant flood potential focuses on the Susquehanna main-stem (and NE PA tributaries), especially in the Upper Sus Valley on into NE PA where that particular region has the trifecta of significant rainfall, the most significant existing snowpack, and a several hour period where warm temps via southerly flow punch up into eastern PA to further enhance a more rapid snow melt. Short range models like the NAM have been downright excessive with rain totals, and the next several hours this evening will reveal if that comes fully to fruition as radar trends look to be starting to focus the heavier rainfall rates into eastern PA along the Susquehanna. The other major tributaries coming from the central counties (West Branch and Juniata watersheds) look to have a significant rise but most point forecasts appear to stay below flood stage along those rivers. Temps in this part of C-PA are locked into the upper 30s-low 40s and as mentioned, heavier rainfall is starting to focus towards eastern PA. Appears that any surge in temps in the central probably comes close to/with the frontal passage as the stable b-layer gets mixed out. Lack of big time flooding coming from those two tributaries probably prevents the main stem from going full blown '96 repeat in lieu of a more minor-moderate flood event coming primarily from upstream in NE PA/southern NY. Definitely not ideal anyway you slice it, what an ugly Christmas Eve weather-wise.

This lead up to the Christmas holiday is definitely looking like it's going to deliver a hard lesson about most of this region when it comes to December snow. Something to the tune of the only guaranteed White Christmas is one where it's snowing on X-mas Day haha. I'm not sure that the portions of north-central PA that got the tremendous totals are going to see a complete pack loss but it's going to get a pretty big dent in it from the Christmas Eve system while the rest of us probably lose the majority of it. Just was hoping to avoid that long drawn out event with the strong cold front but we're going to get a pretty good dumping. Still a bit uncertain about any changeover, that seems the favor from the Laurels west in PA currently and it might be even further west than that with the possible snow swath. Models drawing that secondary low pressure wave that rides up the front through the middle of PA is a pretty good recipe for a slot and shutoff of most precip by the time the cold air's all the way in. At least this storm system will be a one day affair and send some pretty decent cold in for Christmas Day. Then heading towards New Year's we have a good pattern setting up with the nice -NAO block and overall high heights near the pole. So good chance we'll have one or two shots at an event between Christmas and New Years. Here's the possible problem I see, and we got a dose of this problem the last couple days. I'm kinda worried about the amount of cold air we might have in this said favorable pattern. A look at temp departures of our source region in Canada on the models shows a fair amount of above normal temps and not really any bouts of big time cold building with respect to average. Obviously, above normal in Canada is still "cold", but that air mass modifies as it gets to our neck of the woods. I'm hoping we don't waste a couple serviceable storms on account of not having good surface temps to work with (see the last day or so).

Same, it leveled up at about 34ºF most of the night last night and it hasn't been below since. Def shrinking the pack some here (which has no sleet in it). The active northern branch on the heels of the big storm has kept temps moderate at night with the exception of the one clear night Saturday Morning.

1.5" this morning and still snowing lightly.

Might get a period of light snow this morning over there but probably little to no accumulation off the mountains as best precip hasn't been progged to get much further over than western PA (although this is def overachieving here). It appears the clipper might have a better chance of delivering lighter accums (up to an inch or so maybe) out to at least some of the Sus Valley, despite clipper low track going a bit to the north.

Snowy start to the day here, working on an inch and a pretty good burst of heavier snow currently.

Yea, this was why I didn't like seeing the more amplified solutions for this particular system. I'm a build the snowpack kinda guy when it's DJF, I hate starting over lol. Euro op dumps a lot of rain on spots with the big time snowpack, and in general really. Progresses much slower with the front, dragging this affair into the first half of Christmas Day before the cold air gets back in. GFS on the other side of the envelope getting cold rapidly back into pretty much the whole region on Christmas Eve before midnight. Doesn't have as much rain as the Euro and has been the one leading the most with that anafrontal type deal. Still punches LSV into pretty warm temps for several hours. All in all it looks like a 12-18hr period encompassing most of Xmas Eve where temps get up into the 40s-50s in most of the region. I just want to get the front through as fast as possible.

On the X-mas eve system/arctic front passage, not to be pessimistic but Models shifting toward the slower, much more amplified solutions is definitely a case of be careful what you wish for. For our region this may work out in western..perhaps some of interior central PA but I personally don't see much upside to this in the Sus Valley. GFS is the better scenario, focusing on the second wave running up the frontal boundary. Yea there's some snow to be had but it also delivers a ton of QPF (a lot of it rain) beforehand in eastern PA. Euro's even worse with more of a straight up lake's cutter and less emphasized secondary low that probably wouldn't change precip over in time for much. That sends a bigger warm push and 1"+ of rain into places that just got a boat load of snow before maybe a few hour period of snow at the end. All in what you want I guess. You might see that period of snow at some point X-mas eve to X-mas morning, but you might lose most of the pack to see it. I'd rather see the front progressed through faster and maybe set the next event up. Pretty far out in range yet for now, but it does seem like models are heading toward making this more of a QPF laden event. In the meantime there is a couple other weaker systems (Sun/Mon, and Tuesday-ish) to resolve, as one of those systems could muster up enough to put a swath of something across a part of the region.

I'm trying it out a bit. Main thing I'm having trouble with is it loading the radar image really slow.

Plot twist, it's snowing again tonight here.

Same here over on this side of the Laurels, got a fresh coating so far. Pretty nice aggregate flakes too.

You guys seeing much out of this patch of snow in the western half of the state this evening?

At any rate on to the weather going forward. I'm not seeing too much system wise between now and Christmas, other than maybe some kind of weak system at the beginning of this coming week. Temps are meh and setup kind of favors western and Laurels if there's any notable precip. Models have been pretty solid on an arctic cold shot crashing through on or about X-mas morning. Difference between models are on handling the frontal system. GFS has generally had an anafrontal look to it, with a rain to snow scenario with the frontal boundary. The Euro has a pretty dry frontal passage ushering in the very cold air. 12z Canadian had something insane that's not likely to happen, or at least I'd hope not. I don't think either the GFS or Euro scenario will completely erase much, if any of the snowpack even in most of the Sus Valley. As such, chances of a white Christmas (inch or greater on ground X-mas morning) seem pretty good. Zonal flow regime predominant for the next week, which will keep temps pretty seasonable. Also helping will be the presence of our new snowpack, which aside from the wildly varying top end amounts managed to give all of us in here and our western PA friends 10"+ plus sleet to anchor the pack in the LSV where it would be more vulnerable to a WAA intrusion. But a couple days of 40 or so this time of the year isn't going to melt things a ton, especially where the sleet fell. The only day/period that may be notably warmer is around the 23rd with that approaching frontal system. That may have more luck advecting warm air on a SW flow on the other side of the Laurel's but may not do much in central/eastern. Pattern wise going to the start of the New Year, it seems pretty workable. We neutralize the +EPO, which by the way was pretty positive for this storm that just happened. Build a bit of +PNA in the X-mas period with the cold shot. NAO/AO neutral to slightly negative. MJO staying in the circle on most guidance. I don't really see any kind of an overwhelming influence from any particular teleconnection. So if models latch on to any particular system, especially week between Xmas and New Years.. I'd like our chances of keeping the wintry going.

I was looking back at PennDOT announcements for the district that happened in. They had their section of I-80 on a Tier 1 restriction which restricts tractors without trailers, light or unloaded trailers, motorhomes, personal vehicles with trailers, cargo delivery trucks meeting the definition of a commercial vehicle, school buses unless chains are used etc. I didn't realize they had a 5 tier restriction guideline. At any rate at some point (think it was after the accident), they put it up to a tier 3 from the Bellefonte interchange (I-99) east through the rest of Centre and Clinton.. which restricts all commercial vehicles except loaded single trailers with chains or approved alternate traction device. https://www.penndot.gov/TravelInPA/Winter/Pages/Vehicle-Restrictions.aspx Either way given the ample advance warning of this storm and lane/speed restrictions in place, I'm kinda surprised such a massive crash could occur. Doesn't anyone use a CB anymore? Rapidly changing conditions with a squall is one thing.. but a large snowstorm is a pretty constant condition with reduced visibility and traction.

PSP Update on that I-80 wreck in Clinton County yesterday, 55 commercial vehicles and 11 passenger vehicles. https://wjactv.com/news/local/police-interstate-crash-with-dozens-of-vehicles-kills-2

Your welcome, and actually CTP has just updated their disco. They got all the good details in there haha. Also, they have a climo section for record snowfall.. which this is poised to break 2 day largest snowfalls for December in all the CTP climo stations (UNV, IPT, MDT).

That portion of the disco hasn't been updated since about 10 last night. However, overnight and early morning guidance (6z) have continued to support that notion of a 24+ axis somewhere between I-99 and I-81 northeastward toward the Poconos. Exactly where is likely going to eventually be determined by today's near term guidance as the event unfolds. Still trying to adjust to the fact that we're trying to pinpoint the highest totals within a nearly region wide foot plus in all guidance for us haha. I think CTP has a good handle with their current snow map. I do like that general area of Lewistown to Selinsgrove up to Williamsport for the best opportunity to get to two feet or perhaps beyond. For State College I'm thinking 14-18", but definitely a shot to get past 20 or so. Gonna depend how far back those CSI bands set up the first half of this evening, and to a lesser degree how well the storm accumulates rate and ratio wise during the WAA phase of precip today. If State College does get into the thick of it, I'd look at the 7 mountains region of US 322 between there and Lewistown for something ridiculous. Again, this is pinpointing where these excessive totals might pop up within the general 10-20" this whole region stands to see. Making a fairly safe call of 14-16" for the backyard (Altoona), it's weird saying that much is a "safe" call haha. They're sort of in the same boat as State College with perhaps the outside chance of seeing 20.

Way too early look at the 6z HRRR which extends out on the 0,6,12,and 18z runs seems to jive okay with things. For some obs here, it's a nice crisp 26ºF currently with some increasing clouds and a light easterly breeze.

How do you feel about good ole Williamsport being a snow chasing destination for this storm? Haha

Unless your already booked up in Williamsport, since your leaving early in the morning I'd have a good look at 0z and 6z guidance to make sure the swath of excessive snowfall is still going through there directly. A couple backup options might be State College, somewhere up US 15 between Harrisburg and Willamsport (Selinsgrove-ish) or Lewistown on the US 322 corridor that goes between Harrisburg and State College... although I think any of those options are looking pretty good at the moment haha. All those places have pretty good roads so I would imagine they'll be reasonable by Thursday evening since this is supposed to end by daybreak Thur. If they aren't, well then you probably picked the right place for your snow chase haha. CTP mentioned about CSI banding in their discussion, that's the kind of setup you could easily get thundersnow or certainly very intense snow rates out of. And lastly, I'm still on the fence with these Jan 2016-esque totals that persist on model guidance. Within what looks like pretty much an area wide 10-20", I certainly think at least a thinner stripe of 2'+ is possible anywhere between I-99/220 and I-81 depending on where these intense bands set up. These bands are likely to have better temps aloft in the snow growth layer to boost snow ratios being located in the central part of the state. A 30" is doable, but that would be one heck of an experience to get there since this looks like about a 15-16hr storm.

I honestly don't see much change from 12z to 18z or really anything major from model to model at 18z in terms of the surface track when comparing stuff. I'm not going to chase every random kink or secondary max in the isobars. Everyone's going to get a significant snowstorm. Where the best 700mb forcing resides is going to be where the top end snow totals are going to be found and the amount of warm advection aloft is going to determine what kind of mixing issues occur in the LSV, specifically below the turnpike. Model's aren't quite honed in on either yet, especially the mixing. The 18z GFS basically tracked the surface low pretty much the same the 12z as did the 12 vs 18z NAM. Now NAM has looked a bit southeast of the GFS but the NAM sends a lot of sleet (3k had 1-2"+ worth) into the LSV and the GFS basically has the surface low running a straight rain/snow line. The culprit for all of this is not at 850mb but at the 700mb level. There's a huge difference between the NAM and GFS on temps at that level. NAM GFS There was a compromise to be in had in the form of the earlier 12z Euro which is tracking similar to the GFS on the surface. That was borderline at 700mb but generally stayed below freezing at that level and at 850mb where it showed mix.. like indicating a briefer intrusion of the warm nose somewhere in between those levels (probably a more reasonable assumption.

High water mark of the mixing at this 42 hr frame. Mixing at 39 and 42 above mason-dixon. Everyone back over at hr 45. It's hard on these 3 hr maps to really tell whats going on QPF wise but it appears to me the mixing period might conincide with a slot (or lighter precip at least) working up into the LSV, which is certainly possible with how close the low gets before fading. Euros only putting out small sleet/ice numbers and then the backside sets back again as snow. It's still going to be a significant snowfall regardless. Hr 42 10:1 map

Yup I think it would be. 96 and 03 came the closest with 18"ish. Nov '95 was also a 15-18" type snowstorm in UNV. It would be the first one for me personally from an IMBY perspective since '94, which I was 6-8 years old in 92-94 so I don't really remember that golden age for big snowstorms in this corridor. Jan '96, Feb 03, and Feb '10 were all high teens storms (still great events though of course). Just missed the 20"+ by about 15-20 miles in 2016. Hard to do around here, I'll believe it when my homemade snowboard that tops out at 20" disappears tomorrow night lol.

With model's seemingly starting to zero on taking the surface low essentially to the Chesapeake Bay Bridge (the Baltimore one), it's pretty likely at least the southern parts of York/Lancaster have a period mid storm where they mix. I think it'd be mainly sleet north of the mason-dixon line but a low track that close is probably going to introduce p-type issues there for a couple hours. Once the low starts to make it's fade heading toward going under Long Island and New England I think anyone mixing in PA will promptly go back to snow.