jwilson

I don't exactly love the Sunday/Monday setup. We're basically threading-the-needle in a marginal airmass. The 850 vort passes almost right overhead, which is never a good sign. The only thing trying to help is a weak looking 50/50 lowering heights out ahead of the system. In this winter, it's hard to expect all that much. I'm inclined to expect the boundary to setup further north of us because that's been the trend all season and there's no real blocking. The Euro and Canadian are deeper systems than the GFS. That's the saving grace right now.

Exactly, it's a thread-the-needle storm for the coast as of now. We have a little more wiggle room, I think, because if it did occlude and pull west, or even just go negative tilt, we're slightly closer to the cold air source (as weak as it is) and are less susceptible to ocean influences, in general. However, we'd probably like to see more cold air either in place or nearby. The local boundaries can change, but it's unlikely we suddenly find a big pool of cold air to tap. Of course the Euro shows a cutter which matches seasonal trends, so ya know...

My primary concern with the threat next weekend is a ridge axis that's too far east. That could theoretically be overcome with a negative-tilt bomb. The GFS shows a triple stacked low occluded off the coast that retrogrades, but the airmass preceding it is only marginally cold, and it retrogrades so far that it essentially fetches the easterlies off the ocean and warms us up. We have some of the right pieces in place. However, we don't have a true block (+NAO) other than that 50/50 which is trying to provide the confluence, and there's not much cold air nearby in Canada. Maybe some in Ontario/Quebec, but most is confined to the arctic. We'd want that high pressing down to be closer. For now, I'd say the coastal locations are in a slightly better spot, because a massive bomb is always less likely than something that's a little more progressive. But honestly they can lose this because of marginal temperatures and a retreating high.

It's mostly what we'd expect out of a third-year Nina, honestly. We need this thing to die for one: It looks to break down towards the middle or end of next week, if models can be believed. There are coastal signals in that range, but for now it remains a fantasy. A broad trough might set up over the East, +PNA (or a hybrid) and less zonal look.

As for this storm, GFS ensemble plumes suggest a quick inch of snow of the anafront variety. Maybe a little more additional (0.5") from lingering snow showers. That's more or less inline with the OP. It's going to come down to nowcasting because of potential resolution issues on the models, and I imagine the temp change / gusting winds will limit dendrite growth somewhat. That's a -40F temp departure and winds of up to 20 kts.

Should have relocated to Buffalo this year. Some places are going to have upwards of 200" and it's not even January.

Congrats to Davenport, IA and Milwaukee. We're back to an arctic front which is ironically what this system looked more like originally. Problem seems to be we're getting ridging out ahead of the system instead of an LP in the Maritimes which would suppress the flow. Not exactly atypical of a Nina. This is why the big ones are so elusive. Too many things to get right, while getting one thing wrong is easy and messes up the entire formula. The GFSE mean is 3-5" in Western PA, but it's sort of on its own. I think the ground will be slightly white on Christmas, just not the exciting version.

Well a bullseye one week out is usually the kiss of death. Save that run for posterity, though. It's a dream scenario for Pittsburgh. I expected the 18Z to waffle more to the other camp and it barely moved. I guess we'll see what happens at zero hour. Still too far away to guess.

At 12Z, looks like the GFS is all alone. Watch for a waffle at 18Z. The ensembles matching the OP raise an eyebrow, though. Everything else shows a consolidated TPV cruising along an arctic front. Could be Euro's over-amp bias? Maybe, but it has support from the "weaker" models.

They always say the big ones are sniffed out early. Jinx city. Seriously, though, the means on both the GFS and Euro are kind of ridiculous at this range. It's still too far out to say and we could easily get away from bombogenesis, but the signals are there and have been for days now. It might come down to which system ends up evolving into a bigger one (23rd or later on the 27th).

The Euro has an over-amplification bias, as well, and that might be playing into its current solution. The 6Z GFS solution doesn't look quite right. I'd probably toss both.

Yeah the Euro is in-between the Canadian and the GFS. Miller Bs are always threading-the-needle for us, but if we can get the primary to come into the CONUS further south that would help. For example, the CMC has the vort centered over St. Louis on the 22nd. The GFS has it centered over International Falls, MN. That's a massive difference.

If the Canadian verified (it won't), and we only got a foot of snow from that solution, it might be considered a massive bust, anyway. Right now it looks like a glorified arctic front on the GFS. NS dominant and no interaction otherwise.

You have to think the Euro OP run is cracked. It shows LA dropping to 9F degrees on the 23rd. LA's all-time cold record is 28F. That's absurd. The Euro just holds that energy over British Columbia before finally dropping it south. It's a wonky evolution. It definitely remains a period to watch. Everything in moderation, though. Obviously, too anomalous a cold ejection and we end up dry. That TPV parcel can't be too strong, the same as any NAO block can't be overly aggressive. The ridge axis position is ideal in many ways. The question might be whether the confluence over the East counteracts that ridge and keeps the storm more south.

It's too early to get heavily invested, but watch that PNA spike around the 22nd/23rd of December. With an already established -EPO and west-based -NAO block, that's the sort of thing that makes the hair on your neck stand up (if you're a winter weather nerd). The only problem being this is an OP, off-hour model run at 250 hours. lol.

Well, we have a massive -EPO showing up within the 7-10 day range now. I have a friend that lives in Alaska and she got two feet of snow yesterday, and usually downstream that's bad news for us (at present). Obviously, we haven't had much winter weather. But the Alaskan Ridge can change things. Question is whether we can shake that -PNA this month. A big ask, I suppose. Even closer to neutral is better. Very end of Euro (200+ hours) is setting something up, but the GFS looks even a little better maybe. We'll see whether these looks hold into next week.

Keep in mind, models tend to exaggerate pattern changes, even transient flips. They move too quickly. I said it earlier that the change might be appearing too soon in model land. It's more likely to be a gradual shift with lull days in-between. If we get to the 15th or 20th and the better looks still aren't established under 7 days, then it's probably fair time to wonder if a change will happen at all. Though you still need to see how the indices adjusted in that period. Basically, if the pacific hasn't improved in the last few days (and it hasn't), then the long-term better looks will keep getting pushed back. Really, this is typical for a Nina December (-PNA).

I admit I'm not too focused on discrete storms or threats just yet. Mostly watching the upper atmosphere and seeing if it cooperates. Getting something on the front-end of a potential pattern change would be a big win, however. For now I think we're simply in a holding pattern. These are OP runs so the usual caveat, but the 0Z Euro from yesterday compared to today are starkly different in developing a better pacific (incoming -EPO versus positive and a more natural +PNA look).

Mid-month we transition to a neutral or +PNA, usher in a big -NAO block, and seem to keep the -EPO and -AO. Those are the good things. It's possible we're breaking the pattern down too quickly and delay by a week or so, which for the white Christmas lovers wouldn't be a bad thing, necessarily. The issue for me is whether that -NAO manifests as too strong and acts as a true block over 40N. That would be great if you live in Raleigh, but for us it's potentially bad news. The placement retrogrades west enough to entice us. December of 2010 wasn't bad here at 12.2" total. It's a top analog. It would require more research, though, to determine how exactly we got that snow over the month. Was it synoptic or just lots of little lake events? Long-term, I don't think any pattern is locked-in. We're in a volatile situation where La Nina corrodes and leaves us with a sort of bouncing atmosphere.

Well, our average has skewed up a tad because of two years ago, which happened to be the 2nd best December ever (behind 1890). If you look at patterns, I'd guess we're due for another single-digit total next month. Perhaps even another dud. The only instance of snowfalls snapping back that quickly were across 2010 to 2012, where you had a bad year sandwiched by two better-than-average years. Granted, this is weather and quite literally anything can happen, but historical trends don't suggest a big total this December. For whatever that's worth - and to be fair that may not be worth much. Average December snow since 1989 is 8.12" and it was 7.73" before 2020 happened. That's a pretty big jump for one season. We've only hit the average twice since 2014 (2017 was 13.3"). Before that mini-drought we had actually had a strong run of good Decembers. In the preceding seven-year period, we hit the average five times, four of those in double digits.

I would agree. It's quite rare for all of Pennsylvania to win in a single snowstorm together. Usually it's one section of the state that wins while other sections miss out entirely. Most common I'd say are eastern sections, then central, then western (for the big ones). Erie is its own climate because of lake effect, thus they win the most. For synoptic setups, though, 2010 is the rare example of Pittsburgh and Philly both winning on the same storm. Pittsburgh seems to do better when the coastal sections do worse - meaning more inland tracks. A marginal La Nina isn't necessarily as bad for us here. I think the +PNA is the dominant driver anymore. Spotting that ridge in the right location allows everything downstream to flow into the right place. Too much of a -NAO pushes storms away from us, either south or into the coastal plain. A +NAO isn't as negative for us because of our inland and more mountainous orientation. Lows riding the spine of the Appalachians are ideal in many ways. Cold air sources are easier to come by locally. Basically all the same reasons we do better with clippers. The PNA can also influence earlier development down into the southern states or Gulf of Mexico. That's important for us because we don't do Miller B's here. They strengthen too late.

I think "higher lows" is the more expectant result of climate change, overall. Regularly hitting new highs and maintaining hotter temps isn't necessarily the most measurable change. More humidity, higher wet bulbs at a more consistent rate is also an extension of that. There are a few places on Earth that are actually becoming inhospitable to humans because of their increased and dangerous humidity levels (like locales in Pakistan, for example).

Maybe my memory has failed me, but I remember a tweet from the NWS that said July averaged more thunderstorms than any other month, though I was looking at the severe climatology and you appear correct. June has more tornadoes and hail reports, at least. I can't find historical data on severe watches/warnings or t-storms, overall. Guess I'm a doofus lol.

July is usually our peak severe month. Been pretty quiet, overall. I'm assuming we're going to pay for this later with a soggy fall or something.

What's with the security bubble over Allegheny county recently? The storms keep dodging us to the north and south.