wxsniss

Someone asked about HRPDS... Doesn't carry much weight this far out, but 0z actually very close to 0z Euro... big hit for much of interior central-eastern SNE / southeast NH / eastern ME

Given how steady Euro has been last 3 runs, I'd say NAM not latching on to anything other than noise Assuming dynamics can overcome 2m temps, which I think they would as depicted on Euro, getting more confident for 3-6" in Boston area Obviously still some fluctuations we'll see in the next 12 hours and will wait until 12z suite tomorrow for final calls

Euro more or less held steady 12z and 0z runs

Through 36, no drastic changes vs 12z, maybe a tic east but very close

Huge hit on 0z GFS, NW of 18z With 0z RGEM and ICON also NW, 0z NAM is now looking like the anomaly

Yeah I'm looking at soundings on Pivotal... for example between 495 to ORH... 850 and 925 are plenty cold where it's showing heavy rain... I'd expect the 2m temps 35-37F (if those are even correct) should be overcome with the intense rates it's showing

Verbatim 0z RGEM thermals are suspect... has heavy rains to at least ORH

0z RGEM made a decent jump NW thru 42-48h Not weighing it significantly until within 36h, but it's bucking the 0z trend so far

An improvement over 18z with better stream interaction earlier... but at 12z Saturday, H5 overall remains a little more open when on today's 12z NAM it was already tilting... keeps things a little more progressive Wouldn't make any definite trend conclusions before 0z tonight

Box AFD (Nash) with quite the self-deprecating, open voice... and a message to hobbyists to boot... some excerpts: Models: still quite a bit of variation and the models are struggling with exactly how a northern stream disturbance currently diving south along the Ontario/Manitoba border and southern stream energy across the ArkLaTex region will merge later tomorrow... A 50 mile difference in track, or 6 hour timing difference in development means all the difference. What I`m trying to say here is make sure you have big error bars around the forecast. This is a great situation where probabilistic forecasts are much better than a single deterministic one. But since I`ve got to make a deterministic forecast, we`ll just have to work with it. Scenario:... NAM is believed to be a little too far east. More or less went with a 12z Canadian/ECMWF concept... Snowfall: ...I went with about 7-8:1 ratios during the day Saturday. As we get into the evening, rising to 9-11:1. For those playing at home and viewing snowfall predictions from online weather models, please be aware that most use a strict 10:1 ratio which will get you into trouble more often than not. Although I`m going with the lower snow ratios, there is an unknown if we end up getting a mesoscale band or well developed comma head forming. If that were to happen, that means we`ve got strong vertical motion in the snow growth zone resulting in large dendrites and a much higher SLR. After putting everything in a blender, I came out with amounts over 6" across higher elevations of MA with 2-4" widespread at lower elevations. Perhaps an 1" as you get just inland of the coast. Chances of my forecast being perfect? Pretty low. Snowfall amount probabilities suggest the potential for 10"+ across the higher terrain. Later forecasts will hopefully fine tune things.

Model trends in past 24 hrs have attained dynamics of the Euro + more eastern track of GFS... threading the needle for eastern SNE

Yeah. Wish it were a slightly colder airmass, but otherwise Dec 9 2005... hope you can make it back in time.

Only had a chance to go out late afternoon... beautiful scenes. It's striking to see snow with still-green deciduous trees... same as in April. The magic of 2 New England seasons in one shot...

Among other records (shortest interval between snow, 193 days since April 18, previous record was 194 days in 1987)... perhaps the most amazing is that October brought the biggest KBOS snowfall to date in 2020. What a refreshing break from a wretched year. Let's hope for more, it's gonna be a long winter.

Also... weak first showing by the RGEM. NAM did well.

What an awesome event! What a refreshing escape from gloomy news and no home team worthy of rooting for. Widespread 3-6" across much of northeast CT / MA pike region / RI including Boston metro is a lock. There was understandable guardedness of those soundings posted yesterday ("we struggle to get these soundings in some January events"), but the cold delivered. The mesos nailed this.

Eyeballing >2" in Brookline near Coolidge Corner, will measure when get a chance

This never gets old! And drooping trees with leaves covered in snow... amazing sight! Eyeballing 1-2" in Fenway 13z HRRR has some of the best soundings 17z-18z in Boston metro, let's see if that materializes

Gonna be a fun few hours tomorrow morning... we've struggled to get these soundings in some January events... Nice pre-season warmup

Just looked at GFS... terrible 12 hour trend... big jumps in wrong direction... whatever new data was sampled (looks like energy entering BC) is not helping And big changes... in 12 hours, went from "oh so close to something big that is well within guidance margin of error" to "very unfavorable"

Over, no. Less likely, yes. H5 handling has been very inconsistent, though we consistently get crappy solutions. I'd give this until at least Thurs 0z to show hints of improvement. Maintaining the status quo obviously won't do it.

yeah... and less digging northern stream... and more progressive trough... on both 18z GFS and 18z Euro H5 and trough orientation on 12z GFS looked most promising to me, but for a surprise to remain a possibility, these ingredients need to at least hold, not worsen

First post since Dec 2... haven't seen any compelling threats + crazy busy at work... thanks for great discussion here by the usual players as always. But I'm more on guard for a surprise on this one... good H5 setup, and conducive to an abrupt jump rather than gradual evolution of solutions. If all you had was this H5 map, you'd anticipate cyclogenesis ~ under that green circle... the trough is tilting nearly neutral, the flow is not compressed and there's room: Instead 24 hrs earlier this lead energy is stealing the show, purple circle: I know overwhelming majority of OP and ENS guidance focuses on that lead energy shunting this well OTS, while the lagging stronger SWs end up doing nothing, but I'd remain vigilant for a surprise on this one, at least through 12z Thursday guidance.

I and probably eveyone was too exhausted to do a post-analysis... thought I'd toss up some tired and probably incomplete impressions. I went back through model runs in the 48 hour leadup and compared to the obs map above. Thought this was a clear NAM winner. Feel like it's had a good season. Very clear banding signatures that happened. Euro was good too. The old EE rule and ignoring all the other model noise would have given us the best handle of this particular storm. Most guidance wanted to jackpot southeast MA, but between mid-level processes generating bands further northwest and initial boundary layer issues southeast, jackpot ended up in the 495 corridor and extended further north than most expected. RGEM was spastic and more wrong than right. GFS was a national embarrassment, pretty much ignorable. Ok with SLP track, but qpf depictions and thermals were a joke.

Per usual, an anomaly compared to every surrounding site. I'd expect most sites in the immediate metro area (Chelsea, Revere, Hyde Park, South Boston) near 15" after that 5-7pm band. Some other nearby reports: Somerville 19.9 733 PM 3/13 Social Media Revere 15.0 632 PM 3/13