WxUSAF

The ensemble is a certain number, 20-50 depending on the model system, of lower resolution model runs with perturbed initial conditions. A mean of those members is produced at each time step for any particular variable.

Be very very cautious of that. I’d bet good money there would be a 925-850mb warm layer in there with that solution verbatim. Driving pingers.

The apparent “jump” west is somewhat of an artifact of where the graphics routine plots an L. What’s happening physically is the storm is occluding and becoming vertically stacked as it moves through VA.

12z stopped the bleeding, 18z stepped in the right direction. That's all that's worth taking from that.

Couple thoughts/reminders for this type of storm, probably too early: 1. “WAA waits for no one”. Precip usually comes in fast and early from WAA. This is the “thump” we’re talking about. Snow growth usually is meh in this scenario (not fluffy dendrites), so ratios are typically a bit lower than 10:1. 2. The mix line (watch CC radar, hi @mattie g) is going to haul ass northward. Given the likely CAD in place, I’d wag that there will be more sleet than currently shown. That could cut down on the pretty colors on the snow maps. 3. This is a stacked and occluded low, so it will snow much closer to the storm track on the west side than is typical. Hence why even 50-80mi east could make a huge difference to snow totals.

With a stacked, occluded low, you’ll get snow JUST west of the MSLP track. So yeah, wouldn’t take a lot to stay all frozen for the metros. As @psuhoffman said, the phasing of the energy on the back is really the key here. Delay that a little or have less phasing and it slides more NE instead of N. If people are bailing on this storm, they’re crazy. I want all snow, but I’d take a 4-6” thump (Hi RR!) all day and night.

Thump, mix, dry slot. Can’t tell how long it rains with the 6 hour maps, but I’d guess not a ton.

Probably safe to say CMC is going to be our least favorite 12z model…

Not really. Although the objective stats have it better than the GFS typically now.

B/W maps are rolling…and yikes. They did not get the memo that 12z was supposed to stop the bleeding.

Did Canada’s computers break this morning?

Exactly that

Yes

Yup, I think that’s very much on the table. I think that’s pretty close to what last nights euro showed for many of us.

One small feature I’ve noticed this morning is the vorticity streamer oriented E-W between our shortwave and the upper low in New England and Atlantic Canada. On my phone so can’t post a graphic, but it shows up very clearly at 84hrs on the GFS, NAM, and Icon through the Great Lakes. Seems like it does help lower heights ahead of the storm. Not sure yet how much it may shift things, because it’s a subtle feature, but I’m going to watch that today.

That WAA snow will be a beast. Have fun Sunday afternoon/evening watching that rip, have some drinks and watch football, and go to bed before it flips. Great day!

End result is pretty similar to the last few GFS runs, but for this run at least, the stronger/slower/wester trend stopped. Maybe a blip, hopefully a start. But a step of that size each run puts us in great shape by Sunday

For sure. It’s 6-8 hours of thumping WAA snow then probably mostly dry slot.

6z euro only goes to 90 hours.

Totally agree. We’ve seen such huge shifts within 60 hours of storm start this year already! We’re at twice that range almost! This storm already had a massive shift in presentation yesterday! I’d say we have AT LEAST until the 0z Friday runs if not more time for positive shifts. That said, 0z euro is a solution I’d still pretty happily take for MBY…

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