ORH_wxman

This is a really messy map below (96 hours on EPS and 120 hours respectively)...to agree with your point. I don't think we can write off even the weekend event as a total lost cause. Particularly for NNE. We'd need more help in SNE for obvious reasons, but you can see what is going on there....a block in the WPO region (building and rolling over into the EPO domain) with a pretty soft AO/NAO....almost a "ridge bridge" forming there. You also have split flow out west. Add it all up, and that's the type of look where you can get corrections to colder outcomes. If not enough in time to help this weekend, perhaps the event behind that one.

We saw this in Dec 2008....here is the 5-6 day forecast for 12/19/08...the last image was how it turned out. Doesn't alays work out like that of course. That was 12 years ago....but even now the models have a lot of toruble in Nina with blocking up near AK.

Almost looks like 12/16/07 with that high location. Maybe shove it southeast just a shade.

I dunno...the max snowfall for the eastern zones in MA was really like 4-8pm on the model guidance....I agree the models did seem to go on too long after that, but the core of the best stuff was forecasted mostly late afternoon and early evening....which from a rate standpoint, largely verified. Maybe we're having two different discussions here..... 1. Did downsloping affect things later on? Yes. The precip after 7-8pm did not really match model guidance which suggested perhaps 2-3 more inches for E MA even at modest 7 or 8 to 1 rations. 2. Was downsloping the main reason for the lack of snowfall accumulation between 4-7pm? No (IMHO). I think our cross sections are explaining that better with the "perfect storm" of toxic brew....as Chris said, the lower elevations needed either slightly more LL cold or for dendrites to overcome the lack thereof, and we couldn't get either. Places like BED and LWM were getting heavy white rain...slamming plenty of precip into the buckets, but just not accumulating it on the ground.

I think the lift location is more important than “shadowing” which implies a drying out of the atmosphere. The precipitation was pretty prolific still looking at LWM on the upper 495 belt pretty quickly. I see hourly bucket tips of 0.16, 0.18, 0.12 after 5pm. That is heavy stuff. They just couldn’t accumulate it. It was white rain.

It's pretty clear that Canada will have some cold....at least for most of the Dec 12-20 period. Less clear beyond that. Now if we can get some timing, then we'll certainly have a chance or two.

Yeah Jefferson is still way better than places like Lancaster and Whitefield, but they are on the "same side" of the terrain as them, so that's definitely why there is a notable difference between them and Randolph which is on the other side of those key terrain features. The snowfall seems to really increase once you get into the "curve to the east" part of Rt 2 about a couple miles east of downtown Jefferson.

It's not a great pattern but watch that block N of AK....that can sometimes wreak havoc on the modeling as arctic shortwaves dive down east of it and perhaps give us some colder solutions than guidance currently suggests. We've seen that plenty of times in the past....it's basically the opposite mechanism of how when there is a death vortex over AK, we often see things trend warmer the closer to verification we get. You can see the progression of the block N of AK...it eventually retrogrades and weakens, but it is something to watch because that type of block usually biases results a bit colder. Also watch the eastern NAO stuff as well.

The old Jefferson coops and the NORHC snow map archives showed a clear decrease of snowfall into Jefferson vs Randolph on the other side of Pilot/Pliny range.NE wind def downslopes them and they don't have the CAD capacity that further east does.

Probably the ugliest above average pack duration winter of all time up there. I wonder how many days it was a crusty 2 or 3”.

The only winter in the mid/late 1970s that came close where you were is prob 76-77 but even that winter had most of December with no pack after the late November snow was torched away by a cutter. Ditto ‘77-78 but even less close.

We actually have a pretty stout EPO ridge this week/weekend but we get a cutter with it (most likely). Shows the risk of EPO ridges at times. Theres probably a window behind the cutter to get something.

Yeah it should help at least keep some cold nearby. It’s going to be above average for that period but that look still gives a chance for something unlike the more classic Death Star pattern.

Looks a bit like the last 10 days of dec 2007 or so...there just enough WPO to push the lower heights further south into Canada and the western US. That was an above normal period for us but it did have some threats and a couple advisory events.

This crap was like slime and then froze overnight. Back in holliston we got about 4” of Italian ice. But the piles make it look like double that because of the water content.

If you want to hone in on a narrower range, I feel like the best period for us is probably like 12/16-12/19. That’s when there’s some cold established nearby (or hopefully over us) and could work with an imperfect synoptic setup.

They didn’t. Unless maybe you live in Norfolk.

Yeah you’re left with like these -5C needles falling into that deep 32-33F layer. Not a good combo for efficient accumulation is an understatement.

The lift was lowering throughout the event over E MA. There was prob more DGZ lift during the initial changeover than later on...maybe Chris or someone has easier access to the cross sections than I do at the moment, but I’m pretty sure i recall seeing the lift a bit deeper earlier in the event. Usually once you flip over to snow, keeping excellent DGZ isn’t a huge deal because your in the CCB and often advecting cold air into the system...but this was a unique system in which we were not so the issue ended up more glaring than it usually would be.

And the best zone that had decent lift in the DGZ was further west over ORH county into adjacent S NH...so they had the double advantage of better DGZ lift plus some elevation. It’s probably why you saw like 9-12 inches of snow there while Ray in Methuen was struggling to get 2”. You hardly ever see that type of gradient unless he was mostly raining which wasn’t the case.

Yeah this almost certainly a factor too. Even in warm spring storms, if you have a dry polar high sitting up there, it can be a nice source of drier dewpoints feeding into the storm to help cool the low levels even if temps were 55F the day before. There was probably a combo of factors that hurt further east. Less loft in the DGZ, lack of drier dewpoints up north to help advect in a source of lower level cooling.

Yeah I’m not sure. The temperature of the ice matters too. I’ll have to search for the paper I mentioned...I think I have it saved on my pc downstairs. It’s like my go-to source for this kind of stuff. It talks about everything including how you can get ice crystals in areas close to the ocean as low as -4C to -5C due to the salt nuclei being far more efficient at warmer temps.

Yeah if you’re throwing a bunch of marginal ice crystals at relatively warm temps (like around -5C as you said) into a layer at 32-33F, that sounds uglier than throwing a bunch of hooked dendrites at -10 to -14C into that same layer.

I have to go back and find that great paper about dendritic and ice crystal growth but I also remember from it that it talked about how the well-formed dendrites/ice crystals will latently cool more efficiently when they melt than marginal ice crystals. So kind of a double whammy there in a super marginal air mass. There was a ton of QPF that fell in the CCB...agreed on that. So it wasn’t like we got dried out over E MA. It just ended up basically being sleet ratios there.

Zwyts sent me a pretty sweet video of solid wind/snow combo. I told him I was glad in retrospect that you guys went with the more elevated zone vs lower down on skowhegan/Millinocket...being at 1200 feet ended up being a bigger deal than initially thought. Y’all hovered just below freezing which was huge.