psuhoffman

the guidance was too slow on retrograding the longwave pattern last week which lead to this past storm going from a TN Valley/NC blizzard to eventually a OH Valley to New England blizzard. And the same trend is continuing right now, if it does continue the same exact error….well we’re all thinking it! The whole pattern is retrograding and reloading. Just as the current block is retrograding into the west and dissipating the next Scandinavian ridge is about to retro into Greenland next week! Think the last 9 years when we were often stuck in a feedback loop of never ending suck. This time we’re stuck in the feedback loop we want with the consistent being a permanently weak AO all winter that looks to continue frankly likely the whole cold season. We’ve slightly underperformed to this point but we have a whole half (and the snowier half) of snow climo left to correct that!

Oh I’m paying attention. I’m just exhausted.

RRFS held from its previous run showing a general 6-8" across most of the area before the flip

I posted a forecast 2 days ago...it's likely going to bust a little high...this was just a last minute update on what I am thinking...I won't grade this. And it hasn't started for me yet lol

Final Thoughts, these totals include sleet accumulation. Things really started to tighten up the snow/ice gradient the last 24 hours. I see a path for this to bust low...if we do have really heavy precip in the morning between 10-16Z like the RGEM/Euro/GFS/UK show

Naw DCA will report 3.8” no matter what

I’ll put a final map out in a min but some over unders in my head right now DC: 5” IAD: 6.5” BWI: 6.5” Winchester 10” leesburg 8” Frederick 9” Westminster 9” Owings Mills 8”

DC is just…I dunno it’s like they have some snow dome right there. And even when we get southern sliders they often end up missing the real big totals on those to the south.

Yea if we toss the NAM because it’s in its own universe. (Not saying it might not be right but it’s hard to bet on it v everything else) all other guidance is starting to tighten things up right through our area. Somewhere near us is going to be a very sharp gradient with 8-12” on one side of the line and 10 miles the other side only 3-5”. Right now my best guess is somewhere near you to Baltimore ends up near that line and tiny factors will decide if it’s a few miles one way or the other

UKMET is in the big thump camp. .7 qpf in DC before the flip. About .9 Winchester to Westminster before mix

I was trying to be nice but he forced me to say it. The heavy banding is just north of them on the rrfs during that time. It’s more extreme north VA and northern MD nw of 95 that was directed at

Sorry up here it was higher up at 16z. Assumed it was similar further south. it’s super close 70 north. DC not so much. Unfortunately I think DC south is cooked for the bigger snow totals. Things are tightening up and the gradient looks to end up somewhere near a Leesburg to Baltimore line with snow totals going from 3-5” south of that to 10” north or there pretty quick.

The better argument is that the rgem/euro and other guidance that gives us 8-12” does so by sticking an incredibly intense band over us from 10-16z. It’s a lot easier for WAA to win in light to moderate precip than it will be to advance if there is a band of .1 qpf/hr+ stuff over the area. It’s all going to come down to that really imo. The NAM doesn’t have that. It shifts the heavy banding way up into central PA and the WAA routes us because there is no dynamic cooling to slow it down. Basically if this is what’s going on from 10-16z the snow will hold on longer north of about 66 and definitely north of a Winchester to Baltimore line this on the other hand, ain’t gonna get it done Everyone is focused on the temps on the NAM, the real issue is why is the NAM missing the heavy banding tomorrow morning that all other guidance has. That’s why the mid level warmth surges north from 10-15z there is nothing to slow it down on the NAM.

Forget the NAM. It’s 50 miles off everything else even the other cams. But I Caught something on the RRFS. Verbatim it’s meh with 4-5” across the area. But it has an intense band of precip from 16-19z across the area as sleet but it’s super close. It’s only +1 at about 750 mb. Every other layer is fine. This is 700 which is the closest layer I can get represented but it’s close to the warmest layer. If it’s 1* colder across this area from 16-19z it would be 10” instead of 4” This trend has been on the last 2 runs and now it’s super close to a better result

Every storm is different and this is not scientific at all but I do think there is something to this… A couple days ago I said I liked the wedge presentation in the mid levels over 2007 and 2017, examples when the mid level warmer won quick in a route. When there is a clear southward wedge into VA even in the mid levels and the mix comes at us from the southeast not due south or worse southwest we bang on way way longer. IMO it’s indicative of a deeper cold layer that’s fighting more in the mid levels. Often when we bust high on snow in changeover situations it was when the mix was trying to advance SE to NW into the CAD wedge. Unfortunately the guidance has shifted toward a more straight south to north look to the mid level warmth. Unfortunately it’s been my experience that when the mid levels are advancing uniformly through the cold wedge that way it indicates less resistance to the WAA. The one thing that could offset this would be an epic thump which is what the 18z euro and rgem were showing. Thats what happened in Feb 2015, Dec 2013 in situations where the warmth was advancing straight north but got halted by intense dynamic cooling. It can work out but we need to be getting death banded from 12-15z not just light to moderate precip

Use this one. Cut out the area you want.

Go to TT and zoom in on the northeast then pick some 6 hour precip map that has nothing on it and copy it onto paint, cut out the area you want and go to town

So I’ve never seen this drastic of a split between the globals and American run CAMs at this range. What’s odd about this and gives me no past reference to draw on is typically when we see this kind of thing the euro and rgem/HRDPS kind of bridge the gap as those 3 are decent at seeing mid level warming. But they are all in the camp with the other globals (UK/Icon/gfs). The impact is most drastic actually for Maryland. Around DC and south we’re talking maybe the difference between 4-5” and 6-8”. But for places NW of 95 in extreme NW VA up through central MD we’re talking the difference between 5-6” and 10-12”! The divergence seems simple. The globals along with the Canadian high res models have an intense WAA band over the area from 12z-18z that the American CAMs do not. That’s why they are warmer. Less dynamic cooling to fight off the WAA at mid levels. Also less precip. That combo means 6” instead of 12” for places like Winchester-Frederick-westminster. What this comes down to imo is which camp is correct about the precip representation from 12-18z. Unfortunately I don’t have any great insight. Usually here is when I’d be saying “in this or that situation this is what happened” but I can’t remember a single case like this to draw upon. I guess I’m gonna ride with the euro camp. It would be hard to take the NAM and a bunch of experimental stuff over the highest verification tools we have. But on the other hand those CAMs were designed for this. When they score the euro a 30 mile shift in 800 mb temps and a meso scale precip band aren’t really going to impact those scores at all! Yes I just contradicted myself. If I had to make a forecast maybe I’d hedge and go in between even though that’s probably not the most likely outcome, one of these camps is going to win and that zone is either getting 5-6” or 10-12”. So a forecast of 8 would be gutless but the least likely to bust bad. @Terpeast @WxUSAF @CAPE @MillvilleWx Thoughts?

I agree but on the other hand what is reasonable for people to expect when NWS has been predicting 10” in DC for days. Even right now thy lowered it all the way to 9!

24 hours ago we were debating if ice would make it to the PA line...now it's closer to the NY line

Ggem

Rgem

If you adjust the snow/ice line 20-30 miles NW to account for its inability to see mid level warm layers it’s not that far from the ggem and EC anymore

Down to 13 here