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February 12th-14 Redeveloper Nowcast/Obs


Baroclinic Zone

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4 minutes ago, powderfreak said:

Must mean the warmth is nearby.  I love how that happens.  You get the mid-level warmth to cause the smaller flakes to aggregate into bigger flakes as they get slightly wet aloft.  There's probably some spring blue bomb going on at like H7-H8 at 32.1F. 

 That is exactly what happened here, before the flip about an hour ago we had heavy snow with great snow growth for about 30 minutes. 

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13 minutes ago, powderfreak said:

Dead calm here on the eastern side of the Spine with air filled thick with flakes.... while a Wind Advisory is in effect on the west side for gusts to 50mph.

Calm on the upslope (the low level jet is rising to get over the mountains), strong winds mixing down on the downslope.  Which is why we get high winds in Stowe on NW flow.

images?q=tbn:ANd9GcQyFCBsjNQ8B8EMD32ThPH

Edit: Not sure why that graphic is so small, ha.

This is a great explanation, THANK YOU!

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20 minutes ago, alex said:

Really??? How is it that it's a tornado up here and you have light wind? 

 

Make the wind go away lol

Hum,  I don't know Alex.  Mount Washington wind direction is 140.  So that's SE.  Isn't Crawford Notch about in that direction for you?  Maybe all the wind is funneled narrowly through the Notch and comes along the river right through your valley.  It's really interesting because usually it's roaring up here but not tonight.  Just gentle light to moderate snow.

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6 minutes ago, powderfreak said:

This got me thinking how rare it is to get great snow growth in these types of events.  The mid-level warmth is also what's causing the best lift, so naturally as that level warms we lose snow growth. 

I mean you don't even have to look at soundings in these events to know its going to be baking soda or thousands of needles.  Given the size of the flakes up here it wouldn't surprise me if this came in under 10:1 even for part of this.  It's like a fog and air is thick with snow, but they are the smallest flakes you can get.

Never a good idea to stray too far from 10:1 in a SWFE.

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2 minutes ago, wxeyeNH said:

Hum,  I don't know Alex.  Mount Washington wind direction is 140.  So that's SE.  Isn't Crawford Notch about in that direction for you?  Maybe all the wind is funneled narrowly through the Notch and comes along the river right through your valley.  It's really interesting because usually it's roaring up here but not tonight.  Just gentle light to moderate snow.

Good inversion just about summit level, so most likely downslope winds. 

We definitely don’t have the observer networks BTV and ALY do in downslope regions, so we don’t here about it as much.

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17 minutes ago, dendrite said:

1. AWT

2. The NAM had been pretty spot on for 48hrs. I think it was well under .50” QPF as snow for most of SNE.

 

13 minutes ago, ORH_wxman said:

I made a post last night going over typical parameters we want to see for solid warning amounts in a transition SWFE. You want a classic "cross hair" sig on the soundings...that's just a quick way of saying the omega lines up with the snow growth zone...and you typically want big omega too. Not just some 15 micro bars per second maxima. We didn't have a cross hair sig in this event so that is why it is good to stick to advisory amounts. 12/16/07 had a big cross hair sig despite it being a SWFE  it had this bullseye at like 550-600mb where the snow growth temps were.

Point two, which you mentioned, is a good one too. You want a big thump of rates on liquid equivalent. Seemed to start off that way today but then died off after the first 90 min or so. So even with crappy snowgrowth, we could have maybe tickled 5-6" if the rates stayed high...but it's usually good to see at least a tenth per hour of LE on the model guidance. 

Yeah roughly eye-balling HRRR soundings we were under 10 ub/s most of the event, brief maxima at 15 and that was well under the growth zone. Not screaming big thump.

Never really got excited about this event (as evidenced by 0 post count in lead up). I took this more as a quick exercise to refine forecasting of onset / changeover / total accum. An attempt to make lemon juice out of this lemon of a winter.

I expected 3-6" in Boston area based on a NAM/Euro blend, but I'm not sure KBOS even scraped its way to 3". Logan reported 2.2" at 6:49pm. I was counting on more intense rates based on some guidance in the 22z-0z timeframe just before the changeover, but that didn't materialize.

You guys and others had all the caution flags going, and just about everyone in here was tempered. Gotta love the TWC map (? Storm Maya), last night it had something like 5-8"/8-12" for most of SNE/CNE.

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1 minute ago, OceanStWx said:

Never a good idea to stray too far from 10:1 in a SWFE.

We've had a few the past decade that began with a really cold start (near 0F) and that put the first 3-6hours straight in the DGZ since the "warm" tongue was relatively cold. Eventually we would end up pinging in the mid 10s anyway, but that's one way we squeezed out ratios from it. Of course the first few hours of 15-20:1 got a couple of inches of 9:1 sugar on top of it to pack it down in time for the 6hr measurement. By the time the sleet was done the initial fluff in the pack was a distant memory.

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18 minutes ago, powderfreak said:

This got me thinking how rare it is to get great snow growth in these types of events.  The mid-level warmth is also what's causing the best lift, so naturally as that level warms we lose snow growth. 

I mean you don't even have to look at soundings in these events to know its going to be baking soda or thousands of needles.  Given the size of the flakes up here it wouldn't surprise me if this came in under 10:1 even for part of this.  It's like a fog and air is thick with snow, but they are the smallest flakes you can get.

Is it really so rare? I vaguely / anecdotally remember SWFE's with extremely heavy opening thump and excellent snowgrowth before changeover. And how is this impacted by the level/shape of the warm advection in mid-levels that determines where the best lift is...

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