WxUSAF

As always with a coastal storm, there's 1000 moving parts and subtle changes can initiate huge sensible weather changes at any given location. In general, for those of us in the metro corridor, I think we want to look for a few things to make the storm more white than wet (in no preferred order): 1. Increase confluence and lower heights to our north/northeast. This would resist the N/NW motion of the storm and help lock in colder air longer. 2. Increase the forward speed of the storm. It still has been trending slower, which gives more time for our very nice antecedent airmass to move out. Speed it up and it's moving precip into a better airmass for snow. 3. Delay/weaken the northern stream shortwave in the Great Lakes that yanks it north/northwestward. Without this shortwave, this storm is probably a southern slider. We want it to just provide a LITTLE pull to get it up the coast, but not TOO MUCH that would make it cut to Cleveland. Clearly the trend so far has been too much phasing.

@LP08 it's that northern stream shortwave in Canada. In your map, it's up in western Hudson Bay and a piece breaks off and moves through the Canadian prairies and down into the Great Lakes. That yanks our storm west. Without, the Atlantic side blocking is probably sufficient to make it a southern slider that moves out to sea. We saw that with earlier runs. So the positioning and strength of that shortwave is key.

Last evening I was speculating whether the ensembles were "chasing" the Ops. 18z EPS seemed to go the other way, but the overnight runs definitely look like chasing is in progress. Still lots of time for this to wobble back the other way...or turn into congrats Detroit.

DT is riding the #snowtrain https://dtwxrisk.medium.com/tuesday-730pm-update-on-jan-15-16-east-coast-winter-storm-d46de7f907e8

Same. I was kind of wondering if the ensemble members were "chasing" the Op, but if that was the case, you'd expect the 18z GEFS to have looked at least more like the 12z Op (not that 12z and 18z looked that different). But nope...still almost entirely offshore. In general, this is still 5-6 days away, so ensemble means should be where to put your $$. But we have time to see if that's a bad bet.

This is an important point for sure, but the Euro/EPS and GGEM/GEPS having similar looking differences seems very odd.

It seems more than coincidental that the last 3 GFS runs, the GGEM, and the Euro have all been western outliers to their ensemble members. But I'm not sure how much can be chalked up to simple resolution differences since the EPS members are run at comparable resolution to the GFS operational. So I'm not sure what's going on. Luckily this is still 5 days out so we have plenty of time to sort it out.

From the pit of despair, to the top of the mountains, to off the cliff in 24 hours. Never change, weenies.

That storm had the WAA snow come in like an absolute beast. The solutions for the 3 big globals today certainly made me think that there would be a heavy front end snow dump verbatim.

Nope. If you believe the snow maps, it sweeps through with 3-6”.

CCB megadeathband on the backside. Might just stay NW of the metros

TT out to 144. Lol, oh baby.

Storm mode yet??

On my phone so can’t post a graphic, but take a look at 500mb. It’s hard for a shortwave to turn the corner so sharply when it’s still moving SEward and positively tilted coming across the MS river. GFS is about the sharpest corner turn you can see. For it to cut west, it will need to track farther west out in the Plains and/or be neutrally tilted sooner.

Last week I said I thought by Tuesday (today) we’d know if we’re in the game for Sunday/Monday. Think we can say we are. Details will be very much variable for another couple days at least.

Surface depiction at 108 is just classic with a banana high and developing storm in the lower MS Valley. 500 view is less classic, but still has a lot going for it. Eta…120 makes me tingly.

Here I am like a total chump getting my hopes up and looking at the Icon roll in

It’s been since January of 2018 I think since we’ve had a respectable cold air mass.

Periphery of a legit arctic airmass that passed over fully snowcovered terrain and we get a low temp that’s maybe 6F below normal?

Wow…flurrying here

That memory many of you have for forecast failures astounds me. I remember bust events, but I have almost no memory of something that looked good on progs at some point and was clearly a miss by day X.

Didn’t Confucius say it was always over until it starts?

Ok, wanted to make a post showing the impact of the ocean storm on ~Friday to the environment afterward and hence the possibility of a Sunday/MLK day storm. Helpfully, the 3 big globals provided a very nice contrast in this with their 12z runs. Obviously there are other differences that impact the result as well, but I think the ocean storm is a pretty big player to help define the storm track and whether it gives room to the next shortwave/s to amplify. First is the 12z GFS. It produced a very strong ocean storm that was close to shore. For reference across all 3 models, the shortwave that could produce a late weekend storm is near the US/Canadian border over ND/MN in the northern stream. There's also southern stream energy over the intermountain West and southern CA. Next is the GGEM. It's ocean storm is weaker and farther SE over the ocean. It's nearly a cutoff low and just meanders out to sea. Lastly is the Euro. It produces a storm, but it's moving offshore and is "just right" in terms of storm strength. Strong enough to suppress the flow, but not too strong to swamp everything else. Helpfully, also note how the northern stream and southern stream energy already is somewhat "phased" here (all the shortwaves are in line from Los Angeles all the way up to Manitoba). So what happens after? Watch the dark green color, which in this case is the 552 dm height contour, and the light blue (534 dm height). GFS: Look how close the ocean storm is to the surface reflection of our shortwave of interest (the L near Cleveland). Light blue height level right through the Great Lakes. The ocean storm hangs around and is very strong. It suppresses the flow and gives our shortwave no room to amplify. So we end up with a weak frontal passage. GGEM: The storms have more spacing, the ocean low is weaker, and there's TOO MUCH room for our shortwave/storm to amplify. Dark green height contour is well up into OH/PA/NYC. Result? Cutter. Euro: Now it's JUST RIGHT. The ocean storm is nearly as strong as on the GFS, but it's farther OTS. So it's suppressing the flow just enough (dark green contour is through VA), but not TOO MUCH. Hence, our storm tracks farther south and it's bombs away. And yes, the Euro is also good because it phases the northern and southern stream energy. But the storm track is important. Phase the energy on the Euro, but have an ocean storm like on the GGEM and the thing cuts to Hudson Bay and we get warm rain. I think the GFS solution of a strong ocean storm that's close to shore is probably the last likely? 18z GFS was a small step toward a more Euro like outcome. GGEM and Euro like outcomes for the ocean storm are more likely IMO, but that doesn't mean we get a big snowy coastal because that's also contingent on how and if the energy out west phases.

Hmmm…typo then? Weird discrepancy.