jwilson

Looks like this one weakened below severe levels right before it hit us.  The wind wasn't even that bad locally.  Hopefully no tornado up north.  I had a good view of the line from the southeast and there might have been remnants of a wall cloud, but it became clearly disorganized before moving in.  Also didn't visibly see any real rotation.

17 hours ago, KPITSnow said:

Disagree on the not bad part. This is one of the worst storms I’ve ever seen in the north hills. 

Sorry, I meant not bad locally.  I didn't mean that as a universal attribute.

We've been pretty lucky (or unlucky depending on your POV) here locally.  Yesterday was the first storm that actually hit us and it wasn't all that bad.  Most of them have been missing just to the west or east.  Sorry for those of you dealing with problems.  I've seen lots of down trees and flooding elsewhere, including my own old 'hood in Morgantown.

Actually, I've always been curious about this microclimate split we seem to have between north of the city and south.  For whatever reason, it seems south of the city gets much less incidence of true severe.  Does anyone happen to know why?  Is it simple terrain/geography?

I was outside prior to the line rolling in, and you could feel the change before the rain ever hit.  It went from a warm wind and humid day to almost instantly cooler with a cold breeze.  We seem to do outflow-dominant well around these parts.

NWS mentioned yesterday that they've only issued 2 severe warnings so far in 2021, while last year we had 52 to this point.

Seems like a country-wide effect, though.  All measures of severe weather are way down from the averages, including >200 fewer tornadoes than usual.  June and July are typically our biggest months so we'll see if anything changes over the summer.

Looking forward to interesting weather, though I would prefer some thunderstorms to track.  Pretty dull spring so far in that regard.

I remember last April we had tornado warnings overnight.  Two confirmed tornadoes (EF1 and EF0).  Intense.

Current model snowfall amounts across Allegheny county with lower totals northwest, higher southeast:

SREF Plumes: Mean - 5" (ranging from ~3" to a little over 8")

UKMET: 4" to 5.5"

NAM: 2" to 4.5"

GFS: 2" to 4"

Para-GFS: 1.5" to 3"

RGEM: 1.5" to 2"

CMC: 1" to 2"

Euro: 1" to 1.5"

Mesoscale Suite - 

HRW WRF-NSSL: 2.5" to 4.5"

WRF-ARW2: 3" to 4"

WRF-ARW: 2.5" to 4"

HRW-NMMB: 2" to 4"

HRRR: 2.5" to 3"

HREF Mean: 2.5"

HRDRPS: 0.5" to 1.5"

Given the spread of 0.5" to 5" or so, landing right in the middle at 2.5" to 3" seems like a fair measure.  That's where the majority of the models land.  UKMET and SREFs are the high-end outliers, with the latter typically overdone anyway.  Also, important to keep in mind on a number of these, the higher end totals only register in the extreme southeastern area of Allegheny.

Tomorrow morning looks like the best chance for heavier rates, and it is when we could pick up 50% or more of our end total in just a couple hours.  Add on hours of "mood flakes" afterward.  We have a northern stream kicker and dry air intrusion to contend with, plus the best forcing remains well south and east of our area.

If you're rooting for snow, time to hope the south trend stops immediately.  The Euro is probably the southernmost model right now - at least in terms of shearing off the northwest quadrant of the precip shield - but it isn't pretty.  The seasonal trend had been to deamplify systems and kick them south, prevent phasing, etc.  It is possible we're headed back to that norm with the Thursday event.

The NAM has been dropping this system south for four straight runs now.  The GFS jumped from Athens, OH to Athens, GA in a 24-hour period.  Like the last storm there are warning signs, including some of the misplaced upper level features, but we won't really know until we know.

Initial reaction to that 6-8" call is it's too high given the precip maximum on most models for this area hovers around .5" total.  We'd have to average better than 10:1 ratios for the duration to hit 6" of snow.  Under a couple decent bands that can inflate rates and maximize snow growth, that's possible, but I don't see support for it in the models right now.

If you go into the detailed view, anyway, the local forecasts call for a "wintry mix."  We're close on the NAM to that and maintain southerly winds for the duration, but we do stay below freezing at 850.  This isn't the same low pass as yesterday - even if the initial trough position is similar.

53 minutes ago, MikeB_01 said:

I'm also not sure that the probabilities support the watch yet. Someone correct me if I'm wrong ( i feel like we talk about this all the time, but i can never remember), but. i think the criteria for watch/warning is 7in over 12 hours or 9in over 24. 

This varies per region, but in Pittsburgh the watch is 50% confidence minimum in 6" over 12 hours or 8" over 24 hours (or 1/4" of ice).  You're quite close!

An advisory event is 3" over 12 hours, any freezing rain, or a "high impact" event.

1 hour ago, RitualOfTheTrout said:

Lol.. just give me a few hours and I'll be back to form. I don't see any threats after the Thursday deal, going to be weird not having 3 different storms to keep track of, not sure if I'm depressed or relieved over that fact. 

I'm personally relieved and need a break.  I don't mind having stuff to track, but having them stack on top of each other only a couple days apart makes it a headache.  It is quite difficult to resolve anything.  Plus we're coming out of this with nothing significant, so that makes the time sink even more frustrating, at least for us "big game" hunters.

19 minutes ago, RitualOfTheTrout said:

NAM is the warmest model, 32-34 during bulk of the precipitation and gets into the upper 30s before the cold swings back through. Even if we stay at 31, ice accretion will not be efficient. Sure there will be a glaze but it's not a 1:1 ratio like those maps project. 

I can't figure out the NAM.  The sounding profile says sleet, but the surface reflection shows plain rain.  Possible it doesn't matter if it's overamped - although the only meso I can see with an all snow event is the WRF-NMM.

53 minutes ago, Ahoff said:

Weird that this would go west and they'd trend the other east.  I guess usually storms trend east one after another.

Yep.  A more wrapped-up Tuesday storm, traversing into the 50/50 region, could lower heights in the east and thus provide a more optimal path for the system that follows.  You can see in the mid-range GFS how the flow gets flattened by the early week events under blocking.

I'm noticing a lot of the short-term models are keeping the initial thump on Monday relatively dry.  As that looks like the colder of the two "events," that could diminish the overall snowfall totals.  Some models aren't showing a distinct break between the two, but I think a dry slot or period is fairly likely at this point.

Latest SREF plumes are only at 4.5 mean over the period.  Not a great sign, either.

I said it in my last post, but the GFS has been trending this way for days.  The increased probability of ice is only a continuation of that trend.  Decreasing the confluence and influence of the arctic jet up north, while continuing to raise heights in the east with a larger southeast ridge.

Here's the look from 0Z GFS back on Thursday:

We had a fairly decent lobe pressing down and squashing the flow from the south, almost creating a due west-to-east wavelength.  It also compacted the isobars much more concretely and you can see the distance between the lower and upper thresholds is much tighter.  The other variable was the shortwave and in this case, it wasn't as deep.

Then here's 12Z on Friday:

We still have that lobe to the north and it is rather large, but now it is less compressed and has shifted to the west considerably, making it more susceptible to a southerly flow.  We also have a much greater influence from the Bermuda high down in the southeast.  The isobars are still compact, to an extent, so there was hope, but the overall trend was concerning.

Now we come to 0Z today:

The lobe to the north has not only elongated, but also reduced its suppressive force and opened up the flow from the south (SW to NE versus flat W-E).  Part of that is deepening the energy in the central U.S.  However, the westerly trend has continued slightly and the isobars have "opened up" to an extent, allowing for a fast flow of warm air from the gulf and points south.  This is why the 850s will be corroded and potentially even the surface (as shown on the NAM).

The 06Z NAM now gives us mostly rain with the Tuesday moisture.  Caution there as the NAM may be playing its classic overamped card, but it remains a possibility and we'll have to monitor the HREF suite to see if that's worth a further look.  If I had a choice between ice and rain, though, I'd almost certainly take plain rain every time.

In the short-term vacuum, this is much harder to see.  It helps a lot to look at the overall movement from days combined and get a sense of which way this is going.  I was hoping the trend would've stopped last night but unfortunately it didn't, in fact continuing.

Now we're rooting for a much less deepened and centralized system and something more akin to weak waves passing along the cold front to keep us all snow.  That also means less snow, overall.

Agree with others I'd like to see that boundary a little further southeast.  This isn't the typical "warm tongue" progression, but we have a screaming flow out of the south and the gulf as evidenced on the 500H patterns.  There's also the issue of the atlantic ridging, perhaps enhanced by the typical "Nina" response to develop a southeast ridge.  That ridge can be useful for us in Pittsburgh because it can shove the boundary further inland while warming the coastal plain, but there's also too much of a good thing.

None of the models have been great with thermal gradients this winter, and this particular pattern is even more delicate.  I wouldn't be confident in anything.  We'll probably have to wait and see where the boundary sets up on Monday to really get a sense of how this goes.

The GFS trends in the east have been to raise the heights along the ridge and decrease confluence or suppressive cold.  That trend needs to go back the other way a little.

For next week - the setup I had been eyeing - don't worry too much about the thermal profiles right now.  The bigger issue is the ridge and trough positioning.  The ridge axis is way too far west which incidentally leads to troughing in the central U.S.  Less than ideal.

The GFS phases the northern and southern streams and that's why it cuts.  It probably underestimates the arctic lobe up north, but I'm still not sure how these two elements would interact.  The CMC keeps the wave open and positively tilted.  It moves very quickly because of the overall context.

There's still potential here.  The speed of the pattern remains a problem in terms of maximizing that potential.  Maybe we can simply push the best potential back and not lose it totally.  TBD.  We do have incoming PNA and AO spikes that might portend something.

4.5" for a storm total.

The late Wednesday event might be good for 1-3", while the early Friday snow may miss entirely to the south.  Still watching how next week evolves.  The setup is there for something, but the models having trouble with so many pieces.  They can't really determine which to evolve and how.

I thought this radar error was kind of humorous.  Looks like Pac-Man is coming to eat us.

It is hard to love any of these short-term upcoming chances.  The flow is too flat and fast-moving, at least on the GFS.  There's the possibility of smaller events, clipper-like snowfall totals, but if we're looking for "the one," it isn't there yet.  We also have the northern stream polar jet pushing down on everything which can lead to more suppression like today.

The Valentine's day overall view is when things start to get more interesting.  The Miller A-like storm that comes through in 7 days would be in-and-out quick, so the top-end potential is fairly limited.  However, what I'm more interested in is what's happening out West at this time.

While the storm in the East is moving to eject under that intense NS jet, we have a low consolidating energy in the southwest.  This is more or less where we want to see a storm start digging to come across and bring the goods.  The expansive polar jet should move out of the way in time, and the retreating east coast low will hopefully setup in or near the 50/50 region to help create a proper blocking setup.

This is the eventual surface depiction once the above low has moved into the east region.  We see a nice "banana" high up top (crude banana not included).  Unfortunately, at least on the GFS, none of the energy has maintained its integrity coming across the CONUS.  It has sort of dissipated and strung out after crossing Mexico, and it doesn't re-strengthen once making it to the Gulf.  I'm not sure why this happens or if this prediction is even how it would play out.  It is something to watch.

This is the 500H plot at the same time as the surface above.  We see there's nothing particularly interesting happening.  None of the energy has remained consolidated.  But we do have a ridge pressing north on the West Coast, and compared to the rest of the time frame with a fast-moving flow, this ridge might help the trough dig in the East and blow up our storm.  Not quite an ideal axis - slightly too far west off the coast.  Again, for now, just something to watch and see how the pattern over the first half of next week can evolve.

According to the GFS, I think this is our best look and chance for something more significant.  The Canadian has a not dissimilar setup happening out west, but it phases all the energy there and moves it almost due north as a giant wrapped-up cutter.  Looks odd to me.

There are lots of pieces of energy to watch, however, and it is probable the models don't have a good handle on the atmosphere with all the moving bits.  Maybe something blows up short-term and we don't get a lot of warning time instead.

42 minutes ago, Rd9108 said:

One thing this winter has lacked is serious arctic air. Hopefully we get a nice arctic front to roll through with some white bands and then we can get a big storm. I think the models are gonna have a hard time with figuring out everything for a bit. The NAO and AO are negative. We should be going into phase 8 of the MJO and the only issue is that pesky SE ridge. 

A tricky balancing act.  If we go too cold, that's how you end up with cold and dry conditions (which is what was initially depicted).  We need the boundary south of us, but we don't want it too far south otherwise you're talking about North Carolina snowstorms.  Given the Nina winter - which favors a SE ridge - and the negative blocking pattern, that could ideally pinch the trough into the right position when combined.

It is always possible we work through this pattern and get nothing.  Still, like you said all the teleconnections look primed, and any warmups should be short-lived due to cutters pumping the ridge in the east.  While the block recycles, once beyond, cutters won't be possible and the main concern will be suppressed systems.

I see a lot of bigger totals locally but I didn't measure anywhere near that much.  Either unlucky or I screwed up.

Looking ahead ... 

The weekend storm might get squashed under the confluence.  It would actually make more sense for a bigger storm to hit while the pattern relaxes prior to reloading.  That would favor something closer to Valentine's Day.  I count at least six events on the GFS over the next two weeks.  Plenty of chances for any one of them to do something interesting.

In pattern terms, this is almost as good as it gets.

4 hours ago, southpark said:

What would we need for the ridge position out west to help us snow wise?

Generally something more west-coast oriented.  This last time we had the ridge pumping east of Idaho.  That left the coastal too far east for the best bits to hit here.  Trough couldn't flip negative quicker, etc.

We're coming into a neutral (or perhaps even positive) PNA and -EPO regime.  Combined that should help.

I think the bulk of the accumulating snow is done for us.  Current snow depth is under 3" so overall, I'd consider this kind of a disappointment, but not a total surprise.  My estimate from last week ended up generally correct despite some models wanting higher totals in this part of the state.  Without the dry air in the primary, perhaps we hit those totals.  The wound-up coastals rarely get big enough or positioned inland to hit us.

At least we have some potential over the next couple weeks.  Hopefully that Miller A depiction can come to fruition at some point.  The big X factor for us may be ridge position out west.

There were a few models that kept us dry most of today.  We've lost a good bit of time with the primary, but it really hasn't moved much all day.  Consider my last post it was in southern Indiana, and right now the surface low is over Northern Kentucky just creeping into West Virginia.  No coastal redevelopment yet.

The freezing line at the surface is close to the area if not over it, but at 850 the line remains well south of Morgantown.

If the snow rates can get going, it should cool the surface back down, as well.

Still not sure how this will play out.  It does look like we might be relying on the CCB to line up over as again, at least if we want to hit the higher end of warning totals.  Could happen tomorrow and even into Tuesday.  Also consider that the CMC and RGEM has it snowing here until Wednesday afternoon.  If that occurs, we'll certainly be fine.

Looking at this storm overall, however, I can't help but wish we picked it up during an El Nino winter.  That moisture abundance from the STJ would have made this a really remarkable event for a much bigger area.