psuhoffman

General rule with a miller b capture scenario I remember from model diagnostic sessions with Nese at PSU...and it’s worked almost every time historically and over my years of tracking. The cutoff to the CCB heavy snow band will be sharp and right about the latitude that the storm gets captured. There are also rules regarding how far west it gets but this is tucked in so tight we don’t have to worry about that it’s latitude not longitude that’s potentially going to hurt us. Right now all guidance has the capture due east of DC off the Delmarva. Some 50 miles one way or the other. That’s noise. But it’s significant if that 50 miles means a ccb cutoff at Rt 50 v Rt 70! It’s going to be close. For perspective the evolution of this and the current capture location is very similar to Feb 10 2010 with the exception we have a colder airmass in front so a better WAA wave to start. Now that worked out for DC but it was very close. 20 miles south of DC got a lot less snow. 20 miles north got a lot more! So it doesn’t take much adjustment to that either way to have a very different outcome.

Ehh it’s not that radical. The capture happens around 13z on both the euro and rgem. From that point on the low loops around for about 12 hours gaining very little latitude then extends and splits off a northern extension while the southern fujiwaras back south again. That happens off Wallope Island on the rgem and off Ocean City on the euro. Not that big a difference. But when your right on the southern edge...that little bit matters! But the bigger issue is the better moisture transport on the rgem. If you put that from the rgem onto the euro it would still be better. Not quite as good as the rgem but probably could add on another 3-6” in DC. capture moment on both models Euro RGEM

Euro has that inverted trough feature also it’s just not the main focus like the gfs.

I always liked Canada

@Bob Chill wrt part 2 some of it was seeing that NS vort trending south every run. Had that continued it would have squashed this. And we have lost several good opportunities that way recently. Probably due to the NS dominant fast pac jet pattern increasing odds of a random wave up there to run interference at any given time. And the ONLY way I saw us getting blanked was if the wave gets squashed. Even if the ccb doesn’t Pan out a more amped wave imo meant at the least a 3-6” (probably more) waa snow. Mitigating the risk of explains bare ground to my 2 kids!

Wrt part 1 we have a much better antecedent airmass and it’s Jan 31. Even that storm we don’t speak of would have been a 6” snow in DC with this airmass in front of it. I know that because I did get 6” up here with no more qpf just barely cold enough due to my elevation.

Every meso will have some issues with a secondary transfer at 48 hours. BUT the rgem has been consistent. It also has support from its ggem parent. I also don’t know if it has the same issues with convective feedback I know the NAM does which will really be an issue here. I know our instinct is to go with the model that screws us but so long as the NAM is on its own I think it’s just off on a tangent.

18z rgem held, no crazy dryslot and deforms the hell out of us. Obviously I don’t know if it will show the same insane stupid 3”+ qpf but from this we take!

It really tries but it’s made it pretty hard to activate any kind of deform axis with that dryslot it blasted through. I’ve yet to see it to that extent on any other guidance.

The NAMs really have no ccb anywhere in the mid Atlantic because they blast a huge dry slot through and focus all the coastal redevelopment from NYC northeast along the baroclinic boundary there.

NAM is blasting the dry slot way further NW then any other guidance. Let’s hope that’s just a NAM mirage. Everything else about this run is better. And it’s slightly better with the dryslot but it’s still ugly and will make it hard to really ramp up the deform once the dry air has blasted that far north.

Let’s see what happens the fgen boundary that’s going to become the deform is much further south this run then 12z at the same time in western PA and WV.

Another clue is that band in WV/OH because it’s being caused by the same fgen boundary that will eventually become the deformation axis as the upper low and dying primary move east. Seeing that not blast up into Ohio and central PA is a good thing.

Through 30 I see minor but definite improvements on the NAM

NAM is slower with the wave so far, that’s good for the eventual secondary capture

I know that’s the fail option and it’s NEVER off the table in a miller b but not sure I’d use the hrrr at that range.

@Bob Chill it will sting some of the capture is late and the ccb misses. But note as this amps up so has the WAA the last few runs. So even without getting crushed by the CCB the DC area is still looking at a 6-10” snowstorm and that’s if they mostly get screwed which is probably about what it would have been if we got a more suppressed weaker solution. So imo 6-10” with the potential to get 20” if we get lucky with the ccb is better then a suppressed weaker wave where we get maybe 6-12 but there is no hecs upside. But I think some let their perception be effected by the “who gets the most” game. They feel better about 8” if they are the Jack v a 10” storm where somewhere else got 30”. I get it. Envy is a real thing lol. But I always will take my chances on a more amped up storm with bigger upside. These kinds of setups don’t come along that often why be conservative. Our snow climo sucks and it mostly boom or bust so let’s go for boom every chance we get imo.

That’s ok let’s put down 10” in a deathband in those 5 hours then WGAF what happens after.

True but so far the trend across all guidance Nams/icon/rgem has been a faster further south coastal capture at 12z. That’s just good.

We’ve been good. Just this once. Come on. Then I won’t ask the snow gods for a god damn thing for at least 2 years. I swear.

Omfg rgem!!!!!

I don’t think the confluence is the problem. That has to be moving out as the storm arrives or it can’t amplify on the coast and we get a weaker sinking wave and no coastal at all. The problem is the angle of that last vort of the pinwheel to our north comes down in a bad spot and as the trough to our west feels the influence it stretches out positively tilted. That wasn’t on guidance 5 days ago when we were getting 30” bomb solutions here. Confluence has reversed and backed off the last few runs but is still slightly MORE then those epic runs. What changed us the trough being positive on approach which then makes the transfer and capture process take a little longer. Longer pushes that process further up the coast since the low will be gaining latitude UNTIL its captured then it stalls and pinwheels. But we need that sooner v later. We simply need a quicker phase unfortunately if we’re being honest the model bias is typically the wrong way with this and if anything the phase tends to happen slower. Not always though. And the trough is trending better (less positive) the last few runs of the euro and the NAM made a significant jump south at 12z. So DC is still in the ccb game. But the interaction between the wave in the Midwest and that last NS SW to rotate around the Atlantic vortex is what hurt us imo.

You ninjad me again

Every storm is unique. Analogs give you goalposts but yesterday for instance the top 4 analogs included 2 storms that dropped less then 3” on the DC metro and 2 storms that dropped over 20” so you gonna forecast 2-25”?