ORH_wxman

Yeah that looks like a paste job.

HRRR has been moving the snow south a bit each run too.

3k NAM actually gets a couple inches into BOS.

It’s out in NY state

Prob still relevant for December thread but 12/29 still may end up interesting.

Most likely. I see some 31s mixed in with the 32s there in westborough.

Yeah I wonder if ray and SE NH grabs 2-4” overnight.

Gonna have to watch for a flip to a quick burst of snow overnight in E MA. Esp up in NE MA but it could get into BOS and metrowest. Euro has like 1-2”.

Logan finally above freezing now. 33F. Pretty impressive to have that ZR right into the city.

The warmest layer on a lot of soundings was pretty low. Like below 900mb. Kind of a weird event where the warm layer was so low, yet the sfc temps were pretty darned cold. Usually it’s the other way around.

Prob getting pretty saggy back home

It’s also pretty warm just barely aloft. I made a post last night on how warm it was at 925-950mb. So that will also limit the efficiency of the accretion. It’s still really nasty though driving on side roads. But the lesser efficiency should help keep the accretion lower on the trees and power lines.

Merry Christmas weenies. What a nasty ZR event unfolding early This morning. Even into BOS….AWT. Mid 20s over ORH county. We’ll see how fast that warms.

Yeah this is a good cliff’s notes version explanation of the balancing act that needs to occur. I’ve seen so many potential larger ice events become more just nuisance because of too many ice pellets or latent warming to near freezing. Ironically several months before the December 2008 storm, we narrowly avoided a monster ice event on Feb 12-13, 2008. We had pretty solid accretion but it kind of stalled out around a quarter to 3/8ths and then we rotted near 32F with very heavy precip rates and most of it ran off. We just didn’t quite have the dewpoint drain there. Little did I know that it would all materialize 10 months later almost to the day.

I always felt anecdotally in “calm wind” ice events, I ended up at 32.1F pretty damned fast even when starting out cold. It’s nice that subsequent research ends up proving that to be at least a little more than just anecdotes. Also, even back a recently as the 1990s, there was conventional wisdom that the valleys would always be the worst icing spots. I remember reading so many forecasts and AFDs about the CT valley having to watch out for the ice and then I would be 29F and FZRA while CEF and BDL were 34F and RA. It was occasionally true they would get ice while we rained but usually in southerly flow events with in-situ CAD where the icing wasn’t a big deal anyway and would fairly quickly change to rain there…the more serious events were always worse with elevation (at least below a couple thousand feet)…it seemed like the ice climo knowledge was imported from outside New England in many of those instances.

Yeah and I’ve seen it before in a lot of smaller dinky events but in the 2008 event it happened when there was 3” of QPF so it made it that much more noticeable. Like Leominster at 300 feet had catastrophic ice but then if you went to Orange MA on that other side of the spine on route 2 it was almost nothing despite Orange actually being a couple hundred feet higher.

My best educated guess was that the terrain blocked some of the dewpoint advection and it also likely had a mild warming effect of downsloping (and the east side had the opposite effect of mild upslope cooling). In a marginal temp profile, stuff like that will matter more than usual.

There was also a little bit of terrain effects in that storm too. The west Side of ORH hills had drastically less ice at the same elevation as the eastern side that was catastrophic accretion.

Ha we both mentioned 2008 at the same time…nice. Obviously the storm was huge but it was a greaT case study on the different variables working.

The 2008 storm was cool because it had offsetting factors working which kind of made the forecast a really tough call. On one hand, you had marginal temps barely below freezing and very heavy QPF (I should really say rates instead of QPF)….those would limit ice accretion. But on the other hand, you had like a 15-20 knot wind out of the NE…advecting in upper 20s dewpoints the whole time into N MA and down to about ORH.

A limiting factor in efficient ice accretion in this event is that 950mb temps are really warm. Tip mentioned this a couple pages back but that is important because you are going to have warm raindrops pretty close to the surface so they have less time to become supercooled. In many of our nasty icing events, you’ll see 950 temps below 0C and the freezing line is closer to 900-925.

It varies based on several factors but a rough general rule is that 70% will freeze on flat surfaces and then roughly 40% of THAT will accrete radially…which comes out to about 30% of the QPF. So in an example where half inch of QPF falls as ice, you may get about 3/8ths inch on flat surface and 1/6th radial accretion.

Great post….awesome animations in the pattern there. That pattern at the end would certainly be more conductive to coastal storms as well even though the overrunners and redevelopers are still likely favored. At least the meat grinder relaxes a bit. The really strong block in the Chukchi Sea has my attention too. In the past, we’ve seen some really extreme cold outbreaks into the northern tier when a block develops there.

He might need this instead:

I’d watch the Jan 2-4 period for now.