MAG5035

How much did you end up with this morning?

I think their lower ratios down there were more of a result of what was going on aloft, especially in the mid levels. Here’s some mesoanalysis maps at 11z this morning one at 700mb and the other at 850mb. At 700mb, a lot of that subforum was between -2º to -4ºC and was so overnight during the bulk of their snowfall. Cold enough to maintain the snow column of course but those are very warm temps at that level, and would have promoted poor snow crystal growth. They had the better forcing at the 850mb level and 850mb temps were roughly the same as the 700mb temps. 700mb at 11z 850mb at 11z These 850mb and 700mb features were also fairly far to the north, especially the 700mb low.. which was why the best lift probably ended up where it did this morning. I’ve mentioned the secondary max a couple times since Friday, and noted the Euro had it about where it actually ended up on its 12z run yesterday. I didn’t anticipate the big separation between the two though. I expected the 700mb forcing to be in position to boost totals in the bottom two tiers of PA counties. I also expected the meso models to at least pick up on this stuff a little bit prior to the event arriving. They really didn’t.. the northern PA band ended up being more of a nowcasting deal. This was already a fairly progressive system given the setup and positive trough orientation, and I think it just ended up being more so in the end.

Only 1.3” has fallen so far, woof. Starting to get some of this backend stuff but it’s gonna have to do some work. I was targeting about 4-5” here. I’ll be lucky to get 3” to verify the advisory.

It’s pretty evident that some of the better mid-level forcing is currently residing further north. Best band of snowfall right now appears to be residing all the way up between I-80 and US 6 corridor. Looking at mesoanalysis, this coincides with the area of 700mb frontogenesis and thickest dendritic growth zone layer. This may be the result of the 700mb being further north and more robust + temp advection in that layer. 700mb heights/frontogenesis DGZ depth DGZ relative humidity and omega (lift)

Moderate snow here with about an inch so far. 18°F

511PA cams showing it snowing at least as far as far NE as the US 219 corridor between Somerset and Meyersdale, so looks mostly on schedule with the onset so far. Obs here is cloudy and 19ºF/12ºF temp and dewpoint. Nice crisp airmass for a snow event.

It’s likely to be the biggest snowfall DC metro has seen in a number of years, they were 100% overdue for a moderate-heavy event like this. Whatever happens here I think we can all agree that it’s really nice to hash out the details for an all snow event that hasn’t really had any threat of mixing the last few days anywhere in this subforum.

This might be one of those situations that their zones would be better with splitting York/Lancaster in half (advisory north warning south). Either way I have a gut feeling those counties eventually get upgraded for a low end 4-6 warning. As was discussed in my post a couple pages back pertaining to the CTP disco, the shortwave over New England that is the possible detriment for more expansive heavier snow further into C-PA is not going to be in the HRRR’s realm until the 0z run later. So that might be most important model run of our lives coming up haha.

One thing at the mesoscale level I noticed on the 12z Euro is that despite it remaining on the lighter side with overall snowfall it managed to have a secondary band of enhanced QPF that extended from Pittsburgh to Clearfield to Williamsport, giving our northern folks in those spots approx 2-4”. Stuff like that will be need watched for on the meso models as we get close to start time.

Here’s what CTP is alluding to in their AFD on the 500mb prog with a GFS vs Euro comparison (using the 6z run). I x’ed the vort responsible for our storm and the one over northern New England. The arrows indicate the flow, and they converge (aka confluence). I did notice this feature yesterday scrutinizing the 12z models. At that point track and precip expanse was similar on the Euro v GFS but the Euro wasn’t bringing the heavier precip up. That feature above New England was not nearly as prominent on the GFS as the Euro. And as you can see today, both models now have it (A Euro win). I can only go back to 18z yesterday on the comparison, but here’s the 6z GFS (new 12z run is similar) vs yesterday’s 18z run. X’s again denote the shortwaves and arrows illustrating the confluence on the left. Now look at the right one in the circled area (yesterday’s 18z). No closed off low with that shortwave above New England. The flow speeds up in a confluent pattern, and thus as CTP mentioned would limit the window for moisture advection. As I mentioned yesterday, the WAA precip phase was going to be the primary part of the event for most in here outside of the far southern tier (which could catch the back end of the shield with the upper feature passage). So it’s not really an issue of north or south with the actual storm, models have been similar with expanse of precip. It comes down to simply being a more progressive event here, which lessens QPF. Honestly, a good catch and call by CTP IMO by factoring that in their accum forecasts (since high res won’t account for it til 0z) . Now that doesn’t mean we can’t get some north trend back to a degree, but that’s their reasoning for their headline placement… which is solid at this juncture. I think there’s still room to expand advisories a bit, and maybe the LSV advisories to low end warnings. This affects the heavy swath to the south too, as I think we’re back to the ceiling of a general 6-10” event (maybe some 12s) in the axis of heaviest.

The start time spaghetti plot is where it’s at lol.

Actually to further on the NWS and one wanting to get into the reasoning of what they’re putting out product wise, when NWS Pittsburgh issued watches for their CWA last night and posted that to their social media (Facebook). I saw this in the comments. Definitely a candid response, whether CTP subscribes to that method precisely like PBZ does (rarely using deterministic) I’m not sure. But their map products are heavily derived from that NBM nonetheless.

From a northern expanse standpoint, GFS and Euro are pretty close. Where they differ is in the intensity of the WAA precip. It’s an important aspect for us because that’ll be the majority of the event up here in our subforum. Once that low transfers to the coast, it’ll pull the precip shield south and away and we’ll probably miss the back end of the shield that hangs back with the 500mb vort except for possibly the southern tier below the turnpike. That will further add to the DC/Mid-Atlantic folks’ totals. The short term/high res guidance has been coming in hot in the early going with regards to that surge of more intense WAA snowfall. So unless that changes wholesale as we get more into the nearer term, I’m more inclined to go with a more bullish outcome in the southern tier. I think CTP’s watch placement is fine right now. And speaking of CTP, since there was great consternation here (and esp on social media lol) with the rather generous ranges that map product of theirs cranks out. If you select point instead of range you’ll see a much more straight forward map.

Perhaps, NAM is putting out 0.6”-1.0”, with the 1.0” or so being near the DC area… which is probably about the limit given this system not really having a chance to wind up to any kind of full fledge coastal. If this is going to actually crank out a swath of 10-15” amounts it’ll be due to ratios.. which may actually benefit the southern tier. In the NAM’s positioning, best mid level forcing would likely be in the southern tier which could enhance ratios thru more efficient snow growth further aloft. It’s already a pretty cold column as is, with the Kuchera method (which doesn’t account for actual snow growth processes) calculating 15-16:1 ratios for AOO/JST/MDT/THV/LNS. Could be a band(s) somewhere in there that may even best those ratios. Obviously a further south solution takes those dynamics south of the M/D line.

The NAM is indeed a winner for most, but it also has one heck of a cutoff near I-80 in central and I-78 in eastern.

4 trails open right now lol. Presuming they get a clean event Monday and a half decent amount of snow on top of the LES/upslope, it might actually be a good up there next week.

It can keep doing this up in Blue Knob, they’re under a nice band right now.

I’m not home today but here’s the situation there. Some of the snow on the ground is from the inch of wind driven squalls we got New Year’s night. I called in for an official close up measurement of the snowboard haha, about an inch today so far with the snow squall warned stuff still incoming.

I’m not budging from my original thinking quite yet of advisory snows I-80 south and warning snow potential in the bottom two tiers of counties across C-PA. I may eventually concede one or both of those tiers but I want to see the short range play out more, as we’re just barely into range of the NAM/RGEM and not even into the longer HRRR range. That stuff is going to see how the overall precip shield sets up better. I think we’ll still eventually see a more widespread snow shield into PA even if it’s lighter snows and we concede the whole swath of 6”+ to the DC folks. But if that happens the northern tier above 80 and especially NE PA might not see much. Other thing to consider may be a secondary swath of higher snowfall due to better ratios. Lift would be further aloft (700mb level or a bit higher) in a further south solution and temps are plenty cold up there for good snow growth in that scenario with this storm and on down the column as well (less than -8ºC at 850mb on the Euro).

12z Euro is a little bit better than 6z for the southern tier, otherwise still adamant on heaviest swath all the way between DC and Richmond. We shall see how it’s ensembles look.

The GFS definitely shifted south from its 0z position, as did the GEFS (probably an even bigger shift in its snow axis). Might not make much of a difference for most currently, but it def does for our northern folks and Voyager. It was probably a bit too far north the last couple runs, but hopefully we can get the Euro to shift back to meet in the middle. Was just looking at the RGEM and that’s pretty low too with it’s heavy snow, but has more of a widespread lighter snow swath. 6z vs 0z GFS op

Euro ensembles are supporting the Euro op as well. Definitely a large difference between them and the rest of the suite this cycle for our region. But even the Canadian still had good snows across most of C-PA despite having the heaviest swath just south. WB never updated the UKMET to 0z for me but it sounded like that was even further south. Euro itself makes this nearly a non event north of the turnpike. In terms of the 0z cycle the Euro suite is a south outlier with the overall snow swath, and that’s including the NBM (National Model Blend). It’s not storm tracking without a model battle of course. 0z GEFS vs Euro Ens Here’s the 03z NBM (National model blend), and I don’t have 24 hr snowfall for that product so had to use the total snowfall. Outside of the Laurels, SW PA and the NW PA snow belt tomorrow’s event adds an inch or less east of the mountains to that total. Adds 2-3” in SW PA and probably 3-4” in the NW PA snow belt. Honestly, that looks like the best compromise at the moment and pretty much in line with my earlier post with my early thoughts on accums. We shall see how things trend.. we’re still at D4 out from this event.

Ouch lol, completes the sweep of all four bye week teams.

I like where the majority of our subforum sits for this event. Given the setup downstream there’s really only so much more this thing can trend north IMO. Our wave tomorrow, which blows up off the coast and ends up being the deep 50/50 low that forces the trajectory of the main system flat, additionally brings in deep reinforcing cold air to be in place preceding. Even the GFS keeps surface temps about 25-26ºF at best during the storm in the LSV, with the Euro maybe a degree or two colder. It’s no blizzard of 96 or anything, but certainly not a marginal setup temp wise. Temps on up the column are plenty cold as well. I’m not currently worried about any meaningful mixing in PA. DC perhaps, but not after they likely see their biggest snowfall of the last few years. Even there I think the column mostly holds. Worst case is if this trends towards an ICON type track is some mixed for a time along the M/D, but probably with sleet as the dominant mix type. Rough thoughts on accums right now would be most of PA sees 1-2” with solid advisory I-80 south and the axis of 6”+ residing somewhere between the M/D line and the turnpike with the bottom two tiers of counties in good position for potential warning snows. I think the ceiling east of the mountains is a 6-10” type event for the most part, with bigger totals in the Laurels and/or western MD Alleghenies.

GEFS probs of 24 hr snowfall greater than 3”, 0z vs 18z. Big difference vs 18z although the 12z GEFS had similar swath placement to the current 0z run (but lesser probs). Stuff starting to dial in.