jwilson

3 hours ago, Rd9108 said:

Slowly but surely I'm seeing people give up on winter in other regions/forums after this next period. This may just be the year where it just doesn't snow. Obviously we are better off since we don't live near the coast but the long range looks pretty grim. 

It's just one of those years.  I think people have attempted to over-explain this or over-attribute it to other things, but even places north of us have been getting shafted on the snow.  New England included.  Meanwhile, it's snowing plenty out west.

The pendulum will swing the other way at some point.  Maybe not next year but that's not something to predict, really.

Yeah rain in the South Hills.  Changed about 15 minutes ago.  Snow accum of maybe 0.5" before the switch.

Well, not really a surprise.  Will be interesting to see if we get any accumulation.  It's not even snowing all that hard in Morgantown which means quite a bit of virga and dry air abounds.  As the 850 gets closer we will saturate, and as Ritual mentioned we might get some CAA to temporarily cool us.  But then how long before the changeover.

Yeah, simplistically speaking, the unfortunate trend in the short-term models has been to dry this thing out (compare each run from 0Z yesterday to 0Z today).  Areas adjacent to the deform band under subsidence will have the normal issues.

I feel like I've spent too much time on this thing, to be honest.  We can nowcast but I wonder if even 1" for the southern areas of Allegheny looks like a generous prediction.  We'll be warming into the 40s and raining so most will be lost anyway.

We really are masochists around these parts.

This will definitely be a nowcast event.

The SREF plumes are down to a shade over 1" on the mean.  There are three higher outliers (4.5", 5.5", and 6.5").  If you take those away, the mean comes down to about half an inch total.  Pretty dry.

8 minutes ago, Rd9108 said:

Interesting on the HRRR that initial finger isn't as stout but there is a sign of some extremely heavy snow right after that. 

 

It also depicts the surface above freezing at this hour.  Unfortunately, the HRRR doesn't show the rest of the column, but this is likely either a true mix or white rain.  If we do get a period of no precip, it will help to warm things up a little faster.

The NAM at this time shows similar surface temps and marginal 850s (Bethel Park is above freezing while Northern Allegheny is still all snow).  It is drier away from the frontogenic forcing so it makes sense to see us getting warm tongued early.

55 minutes ago, RitualOfTheTrout said:

Not liking the trends here, everything seems to be leaning towards the best thump being just north of Allegheny County. Still a lot of uncertainty though. 

NW of the city (sometimes way NW) is going to be favored in this pattern, but you'd think we could get something being so close to the boundary. 00z GFS provides some hope for that, but even that changes so drastically it's hard to put much faith.

It's near impossible to trust anything in this pattern.

Granted, it's the fantasy range so hardly worth analyzing, but even when the thermal boundary sets up in Northern Alabama/Georgia, the GFS still wants to cut the storm to our west.  It's pretty laughable at this point.

We're just on the wrong side of the boundary this year with everything.  It's probably safe to assume all viable threats will cut until they don't.  No blocking + southeast ridge, absent a well-timed TPV interaction.

GEFS average is 3-4" for the Wednesday event, which would happen early and in marginal temperatures.  SREF plumes average closer to 2" and it's actually been dropping the last four runs.

Like what we saw early this morning, that probably means it's more like a "Snain" (or white rain) and the roads may remain clear, especially if treated.

The NAM depicts a big old dryslot, which certainly isn't unprecedented.  No doubt that would cut totals considerably because on the backend of that dry slot is nothing but rain.  I think the SREF blend (which includes the ARW) is picking up on this, as well, hence the lower figures.

The frontogenic forcing looks great on paper, it's just a matter of whether we see dry air intrusion that cuts the initial band.

Well, at least there's no shortage of activity, even in the long range.  We'll likely continue to have temperature issues, but if we can time something right, we may be able to eke out a moderate event, at some point.

Otherwise we may rely on tiny doses of snow to add up to something meaningful on paper.

There are numerous factors now going against the midweek system.  Unfortunately, it is basically compound interest of the issues we've had this winter.

First, you have a +PNA spike and -EPO ridging all the way up the west coast.  Normally that's a good thing for us, but this is too much of a good thing and it creates a massive slope on the downside of the ridge.  That forces the low pressure down in the southwest to start strengthening too soon.  Normally, that low pressure would gain longitude before amplifying (think of a wave pattern that looks slightly more symmetrical).  Moving west to east instead of north to south.  Instead, it rolls up over the four corners which allows it to pull west as it typical in an amplifying system like this.  Second, we also have a pumping southeast ridge which is raising the boundary out ahead of that low.

If it wasn't for that initial Sunday system, I'm pretty sure this would be a big old Nebraska blizzard.  It would be possible to win in this scenario with a well-time TPV pass or an impressive -NAO block, but we don't have either of those coming along.  The results are, unfortunately, another cutter.  I suppose this can still change, it just seems incredibly unlikely given that the downstream affects can't overcome the pacific and other factors.  The Sunday system can't stall out over the 50/50 region and work as a crude block because - again - there's no -NAO to lock it in place.  Everything blows right on through.  That Sunday system also trending weaker hurts us, although that does give us a better potential on Sunday.

I thought the midweek system had better overall potential, though, and that's why I was somewhat rooting against the Sunday wave.  The Sunday system has a much lower snow ceiling, but I guess we'll take a 1-3" event given how the season has gone.

I really want to buy into that Wednesday threat.  I think it makes more sense, because the Sunday/Monday wave could act as a true 50/50, usher in a better cold airmass and perhaps even rotate in some "loose" blocking in southern Canada.

But a lot depends on what happens with that first shortwave.  It could push the boundary into an ideal spot, or it could move it too far southeast of us and we watch as an ocean storm batters the coast.

In this sense, we might actually root for an overamped fail on the first wave to keep the boundary in a better spot on the follow-up.  A gulf mover rolling through the TN Valley with an earlier coastal transfer looks better and is a more typical winning signal.  It is also harder for a system of that design to gain too much latitude for us.  The cold air still isn't great so it wouldn't be overly difficult to see potential mixing problems.

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.

3 hours ago, RitualOfTheTrout said:

That was my take, the stall \ retrograde would be fun to watch if we had a cold antecedent airmass. Those retrograding situations rarely happen though and your point about the ridge is on point, seeing that I expected this to be much further offshore. Only thing saving it was getting some northern stream phasing going on, but if that's less and the storm is weaker more progressive it probably can't tap what marginal cold is available and it will rain on the coast. Almost a lose lose situation for those guys.

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.

1 hour ago, Rd9108 said:

Euro finally joins the party and has a late phase bomb. Something to track. 

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.