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NNE Heart of Winter


Allenson

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Does anyone have a couple of hundred thousand bulldozers to rent? I want to level the Greens so I can talk about upslope. I just get the downslope from the mountains so when the Vermont people talk about feet I talk about scattered flurries. This system isn't impressing me unless we can get that secondary to really bomb quick this evening. At least my grass will be covered when its all over and done.

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I am really screwing up my forecast with my local plow guy friends. Everyone calls me for forecasts. First yesterday I was saying 3-6 or 4-8" in two batches this AM and then late in the day. Then it became apparant that the first was going to shear off and go south. Still saying 3-6" with the 850 staying south this eve but I don't have the expertise like someone like Brian and he is posting about glop this eve with warm layers and all that stuff. Hope my 25 extra miles north helps this eve. If I end up with pingers and rain my credibility will take a big hit. Maybe the NAM is a bit warm?

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Can you explain upslope and why Vt gets hammered while Sugarloaf doesnt?

J24vt had a good explaination but here's the graphical look...

Basically the Spine is a concentrated area of 4,000ft+ peaks with an average ridge elevation of 3,000ft or so.

There is nothing but flat ground for a looooong way upstream of the Greens. It also probably doesn't hurt to have the relatively moist St Lawrence River Valley and Lake Champlain valley upstream of the mountains, feeding every last bit of moisture into the wall created by the Spine.

Mount Mansfield (Stowe) is sort of the apex of the north-south section of the Spine,and where it turns more northeast up towards Jay. That creates a perfect cross-barrier flow no matter what the wind direction as long as its got some westerly or northerly component.

This is the view from BTV of Mansfield's 4,000ft ridgeline, and that is a true 4,000ft wall east of BTV as the airport is at 300ft, Mansfield summit is 4,395ft. That is a very sharp rise in topography over a very small area so that air is forced upward quite violently at times. That's why we get some awesome snow squalls a lot of the time.

BTV has some radar images from an upslope storm earlier in the season... this had a low inversion level so most of the snow was confined to the western side, but a storm like this will have a more evenly distributed snowfall centered over the Spine.

Figure7.png

Figure8.png

And as Oceanwx said, the concentrated nature of the spine allows for one north-south concentrated area of lift and some of these events get very well developed and it is hard to get the snowfall to stop once it starts... it usually lingers longer than forecast. Clumps of mountains like the center of the Adirondacks or Whites, usually miss out on these events but the northern slopes of the Whites (like Pittsburg to Bretton Woods) usually does just as good as the Greens. Same with the northern slopes of the Adirondacks. Southern Canada is very, very flat so once the air is forced to rise, cool and condense, we get snowfall.

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J24vt had a good explaination but here's the graphical look...

Basically the Spine is a concentrated area of 4,000ft+ peaks with an average ridge elevation of 3,000ft or so.

There is nothing but flat ground for a looooong way upstream of the Greens. It also probably doesn't hurt to have the relatively moist St Lawrence River Valley and Lake Champlain valley upstream of the mountains, feeding every last bit of moisture into the wall created by the Spine.

Mount Mansfield (Stowe) is sort of the apex of the north-south section of the Spine,and where it turns more northeast up towards Jay. That creates a perfect cross-barrier flow no matter what the wind direction as long as its got some westerly or northerly component.

This is the view from BTV of Mansfield's 4,000ft ridgeline, and that is a true 4,000ft wall east of BTV as the airport is at 300ft, Mansfield summit is 4,395ft. That is a very sharp rise in topography over a very small area so that air is forced upward quite violently at times. That's why we get some awesome snow squalls a lot of the time.

BTV has some radar images from an upslope storm earlier in the season... this had a low inversion level so most of the snow was confined to the western side, but a storm like this will have a more evenly distributed snowfall centered over the Spine.

And as Oceanwx said, the concentrated nature of the spine allows for one north-south concentrated area of lift and some of these events get very well developed and it is hard to get the snowfall to stop once it starts... it usually lingers longer than forecast. Clumps of mountains like the center of the Adirondacks or Whites, usually miss out on these events but the northern slopes of the Whites (like Pittsburg to Bretton Woods) usually does just as good as the Greens. Same with the northern slopes of the Adirondacks. Southern Canada is very, very flat so once the air is forced to rise, cool and condense, we get snowfall.

Excellent post PF.

I'm wondering how Stowe and Smuggs can get that much given they are on the Eastern side of the spine? I'd expect amounts to drop off just as precipitously on the leeward side of the MTNs... how much spillover is there?

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Excellent post PF.

I'm wondering how Stowe and Smuggs can get that much given they are on the Eastern side of the spine? I'd expect amounts to drop off just as precipitously on the leeward side of the MTNs... how much spillover is there?

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Mount Mansfield (Stowe) is sort of the apex of the north-south section of the Spine,and where it turns more northeast up towards Jay. That creates a perfect cross-barrier flow no matter what the wind direction as long as its got some westerly or northerly component.

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There is also a principle at work I believe, and it's not necessarily related to upslope indirectly. If you have a stable layer, and moist WNW flow....you'll cause air to "pile up" on top of each other. This in turn will cause air to rise and help wring out snowfall. So basically the air tries to rise up the mountain and contionue to rise, but it can't due to an inversion. What happens is that the air that continues to move in, piles up, and is basically forced upward from this road block of air. You see this out west sometimes.

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There is also a principle at work I believe, and it's not necessarily related to upslope indirectly. If you have a stable layer, and most WNW flow....you'll cause air to "pile up" on top of each other. This in turn will cause air to rise and help wring out snowfall. So basically the air tries to rise up the mountain and contionue to rise, but it can't due to an inversion. What happens is that the air that continues to move in, piles up, and is basically forced upward from this road block of air. You see this out west sometimes.

That's what happened in that big BTV event a few years ago. I forget the date, but I'm sure PF knows it to memory.
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Excellent post PF.

I'm wondering how Stowe and Smuggs can get that much given they are on the Eastern side of the spine? I'd expect amounts to drop off just as precipitously on the leeward side of the MTNs... how much spillover is there?

There is actually a lot of spillover usually... we have the Worcester Range (3,000-3,600ft) ridgeline on the other side of Stowe (the town) and that usually stops the downsloping as the wind just has to go back up over that ridgeline. It really depends on the event... sometimes it downslopes and town gets nothing, other times it snows all the way to Montpelier wayyy down wind.

It all has to do with the inversion level. If it is closer to the ridge-tops, the moisture doesn't make it over and it downslopes really quickly (the above event was an example of a ridge-top inversion with heaviest snows on the western side). Sometimes the inversion is REALLY low and that backs the moisture all the way up into Burlington proper with the heaviest snow (Jan 2-3, 2010 34" record event). If the inversion is way up high or non-existent, the heaviest snow will fall down-wind of the mountains.

I look at it like a mountain wave wind flow with a ceiling. If the ceiling is close to the ridgetop, that moisture isn't making it to the east side and downsloping is immediate. If you raise the ceiling, moisture sneaks over and downsloping occurs a bit further out... raise it way up and have high winds aloft, and the moisture really makes it far downstream and doesn't really downslope until its wayyy out there past Montpelier.

I mean, the Greens aren't like the Cascades so there isn't like an immediate desert on the east side... there's quite a bit of spill over and then you have high westerly winds that push that snow quite a bit out from the parent cloud, too. The snow could be forming over Mansfield but doesn't reach the ground until its out over the town of Stowe, or something like that. We often get heavy snowfall with breaks in the clouds overhead because its all blowing in from a couple miles upstream.

It all depends on the event, sometimes the sun is out in town and its snowing 2"/hr at the ski resort... other times we get 10" overnight in town just like the mountain. Sometimes the western slopes get crushed and we get nothing. I think its all tied into the inversion level.

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There is also a principle at work I believe, and it's not necessarily related to upslope indirectly. If you have a stable layer, and moist WNW flow....you'll cause air to "pile up" on top of each other. This in turn will cause air to rise and help wring out snowfall. So basically the air tries to rise up the mountain and contionue to rise, but it can't due to an inversion. What happens is that the air that continues to move in, piles up, and is basically forced upward from this road block of air. You see this out west sometimes.

You hit the nail on the head... if there's an inversion, the height of it is directly related to where the snowfall is deposited: east side of the Spine, Spine, west side, BTV and out over Lake Champlain.

The big Jan 2-3, 2010 event where BTV got 34" out of no where, was caused by a very, very low inversion. This caused the orographic blocking and build-up of moisture right on the Lake Champlain shoreline. The speed convergence off the lake hitting the land was the kicker in that event.

Figure5a.png

This was from the December event this year that dropped a general 8-14" but on the west side due to the low inversion. This is the sounding to go with the radar images above.

Inversion at mountain level, the snow doesn't get over it. In a storm like this, with a vertically stacked low off to the NW, it'll just be a strong cyclonic flow (surface and aloft) so the snowfall will be more evenly distributed between west side and east side.

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There is actually a lot of spillover usually... we have the Worcester Range (3,000-3,600ft) ridgeline on the other side of Stowe (the town) and that usually stops the downsloping as the wind just has to go back up over that ridgeline. It really depends on the event... sometimes it downslopes and town gets nothing, other times it snows all the way to Montpelier wayyy down wind.

It all has to do with the inversion level. If it is closer to the ridge-tops, the moisture doesn't make it over and it downslopes really quickly (the above event was an example of a ridge-top inversion with heaviest snows on the western side). Sometimes the inversion is REALLY low and that backs the moisture all the way up into Burlington proper with the heaviest snow (Jan 2-3, 2010 34" record event). If the inversion is way up high or non-existent, the heaviest snow will fall down-wind of the mountains.

I look at it like a mountain wave wind flow with a ceiling. If the ceiling is close to the ridgetop, that moisture isn't making it to the east side and downsloping is immediate. If you raise the ceiling, moisture sneaks over and downsloping occurs a bit further out... raise it way up and have high winds aloft, and the moisture really makes it far downstream and doesn't really downslope until its wayyy out there past Montpelier.

I mean, the Greens aren't like the Cascades so there isn't like an immediate desert on the east side... there's quite a bit of spill over and then you have high westerly winds that push that snow quite a bit out from the parent cloud, too. The snow could be forming over Mansfield but doesn't reach the ground until its out over the town of Stowe, or something like that. We often get heavy snowfall with breaks in the clouds overhead because its all blowing in from a couple miles upstream.

It all depends on the event, sometimes the sun is out in town and its snowing 2"/hr at the ski resort... other times we get 10" overnight in town just like the mountain. Sometimes the western slopes get crushed and we get nothing. I think its all tied into the inversion level.

Terrific analysis and insight, as usual. Thanks!

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You hit the nail on the head... if there's an inversion, the height of it is directly related to where the snowfall is deposited: east side of the Spine, Spine, west side, BTV and out over Lake Champlain.

The big Jan 2-3, 2010 event where BTV got 34" out of no where, was caused by a very, very low inversion. This caused the orographic blocking and build-up of moisture right on the Lake Champlain shoreline. The speed convergence off the lake hitting the land was the kicker in that event.

This was from the December event this year that dropped a general 8-14" but on the west side due to the low inversion. This is the sounding to go with the radar images above.

Inversion at mountain level, the snow doesn't get over it. In a storm like this, with a vertically stacked low off to the NW, it'll just be a strong cyclonic flow (surface and aloft) so the snowfall will be more evenly distributed between west side and east side.

The other component to the Jan. 2010 event was that it was tied in with a retrograding low backing in from Maine. The storm was thought to be bringing a wider hit but there was a huge disparity between the upslope area and the rest of the area. i think we got about 3 inches in Peacham.

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Snowing out.

Not storm related, but thought pretty cool to see. You can catch the snowmobile drag races on Lake Morey on the resorts webcam. A lot of weight on that ice for sure this weekend!!

http://www.lakemorey...rt.com/webcams/

I went by the lake this morning--saw a couple trucks out there already (8ish). I've been out there before in a couple vehicles. It's a very odd senseation. Windows open!

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7" in town this morning.... 8.5" at 1,500ft at 5:30am... 9.5" at 6am.

2"/hr and just a snow fog out there.

South of I89 is sort of getting screwed right now. This northern section of the Greens is getting absolutely crushed.

I got a call from a friend on I-89 and he said Chittenden County has no snow...roads are bare passing Bolton. It is ripping, ripping here.

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Event totals: 4.7” Snow/0.68” L.E.

We got a decent shot of liquid down here at over two thirds of an inch, but with temperatures hovering a bit above freezing it has been fairly dense; snow density values were coming in around 15% H2O until this morning’s analysis, where it has dropped to 6% H2O. This event has now pushed snowfall at this location past 80 inches, although it still remains the least snowy through this point in the season out of the last six. The resorts from Stowe northward look to have done well with overnight snow, and it looks like the blitz is continuing north of I-89 based on the radar.

25FEB12A.gif

There’s some wind even reaching down to our location, so we’ll have to see what it does to the new snow and lift operations. The north to south list of 24-hour Vermont ski areas accumulations is listed below for those locations that have updated this morning:

Jay Peak: 15”

Burke: 10”

Smuggler’s Notch: 10”

Stowe: 12”

Bolton Valley: 6”

Mad River Glen: 5”

Sugarbush: 8”

Pico: 5”

Killington: 5”

Bromley: 4”

Stratton: 5”

Mount Snow: 2”

Some details from the 12:00 A.M. and 6:00 A.M. Waterbury observations are below:

12:00 A.M.

New Snow: 2.4 inches

New Liquid: 0.39 inches

Snow/Water Ratio: 6.2

Snow Density: 16.3% H2O

Temperature: 33.3 F

Sky: Light Snow (1 - 3 mm flakes)

Snow at the stake: 8.5 inches

6:00 A.M.

New Snow: 0.5 inches

New Liquid: 0.03 inches

Snow/Water Ratio: 16.7

Snow Density: 6.0% H2O

Temperature: 33.1 F

Sky: Light Snow (2 -10 mm flakes)

Snow at the stake: 9.0 inches

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had to jump the tractor to blow out the snow, but everything is back to winter mode now. over a foot now on the ground from Thurs snow to now, still coming down pretty hard now, under 1/4 mile vis here in the valley. another 2-3" since 5AM.

Spent a few hours up on J this AM. Hooooly!!! wicked good skiing, select your own depth density. 242 was already a mess when the dog and I were heading home at 8, looked like lots of flatlanders realizing the benefits of snow tires, can't imagine what the tour buses are gonna do.

winds were really honking at 6 around 3500', snowing like mad

welcome home mother winter, missed ya.

IMG_2802.jpg

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