I am bored it is cold as hell, let us discuss this Snow Pack scenario

In SW Montana we have had a relatively shallow snow pack again this fall. Lots of facets and lots of sun crusts.

Until yesterday;

Some periods of colder weather followed by milder weather. All last week until mid day yesterday has been mild. At and above 7K during the days: 32F+ with lows in the teens and 20s most nights, mostly clear skies during the day and night.

Things changed yesterday as a moist parcel of air began to move into the region beginning as snow above 7K and rain in the valley. Late afternoon the skies opened and it snowed pretty good. The remote stations are showing 4-6" overnight, around 12" in the past 24 hrs. Temps have dropped off the table and it is now -10F and still going down. Forecast temps could reach -25 or lower through the weekend.

What do folks think this will do to the underlying snow pack?

How about the new snow?

I have my ideas but want to spark some discussion.

I think the warm weather would transform the old snow pack into a stable snowpack on all aspects that received sun and maybe to an extent aspects that didn't get sun. True north aspects won't have all the weak layers destroyed due to radiational cooling.

Things should be pretty bricked up above the freeze line at the time the snow started and soft and wet snow below it. I think this cold air is now going to make bigger facets out of the old layer. Especially if the new snow fell on snow that still had a lot of liquid water in it. New snow will also be faceted, especially at the layer between new and old snow.

wind? you never mention anything about the winds.

rog

Winds during the storm negligible, 0-5 avg, 10-15 max. gusts, NNE. A bit stronger this am, 10-15 with max gusts around 20, still NNE.

High of -6 yesterday -18 this morning, calling for -20 or colder tonight, cold temps expected to linger in the area for 7-10 days, total snow depth around 30".

Our snow pack has officially gone to utter shit.

Spoke with a patroller friend yesterday he said, Heaps of slides on steep N aspects

sounds like lotsa reactive energy in the cold snappy pack. I s'pose if temps stay cold with no new snow, one could wait 72 hours or so and be very mindful of terrain choices/aspect. or pray for a good soaking rain to ridges followed by a good deep freeze. works for us out here and is the best recipe for the blissful supportive corn we get for months starting in march:)

rog

More info please...Slab slides or point releases? gonna guess the latter. Also gonna guess its sliding down to the older layers.

it takes forever for crystals to bond well when it's that cold. Also expect the early facets will keep getting colder/bigger - 30" is not much insulation from those kinda air temps. Trouble is, warmer temps and heavier precipitation will just make it all worse.

Mostly slabs releasing to facets above the ground on N aspects.

Mostly point releases or new snow soft slabs releasing off of southerly aspects.

Pretty much what you would expect.

The wild cards will be East and West aspects. The blow picture is of Lone Tree face, ENE aspect.

Attachment 145869

I have seen new snow releases on this slope but in 9 years, never something like this involving old snow. The slope is steep, approaching 40 deg. but not usually subject to intense wind loading.

From this am GNAFC advisory;

The mountains near Big Sky, West Yellowstone, and south of Bozeman received 10-15 inches of snow with 1.0-1.7 inches of SWE. The Big Sky Ski Patrol continues to trigger avalanches on north facing slopes of Lone Mountain including a slope that does not have a history of producing avalanches (photo). These slides broke on facets near the ground. In other places the weakest layer is the old snow surface. Other slopes may have a fairly strong snowpack and avalanches will only occur in the new snow as the Big Sky Ski Patrol found on some south facing slopes yesterday. With a mixed bag of conditions, look for instabilities in two places: (1) near the ground, or (2) within the new snow and at the new snow/old snow interface. Even though winds have generally been light, watch out for any signs of wind drifted snow which will easily slide.

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Originally Posted by icelanticskier

I s'pose if temps stay cold with no new snow, one could wait 72 hours or so and be very mindful of terrain choices/aspect.

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Me thinks not in a continental snow pack, I think it would get worse with the cold he's talking about.

When thinking about the problem, I kept thinking that the more liquid water in the snowpack the worse the faceting would be from the cold. Is this true or did I cross up something?

Zahan Billimoria
a look at november wx & snow... in some ways quite good 38% ahead of average HS (@raymer today) & even ahead of last year at both rv bowl and raymer. in other ways not so good. the timebomb lurks intact in many hi elev zones and mid/hi elev on n. faces throughout. also buried crusts, SH, NSF problem scattered throughout. skiing is good now & everyone respects the BTNF for a few days after storm...but the dragon will live for longer than that. lets be smart about this year & also have enough respect to be gracious to those who are caught, because most of us have gotten lucky at some point. remembering Live To Ski & Wray Landon



In other words, Rog is an idiot.

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Originally Posted by neufox47

Me thinks not in a continental snow pack, I think it would get worse with the cold he's talking about.

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Correct. Rog is a bloviating idiot.

pretty sure he'll disagree.
:biggrin:
b

Quote:

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Originally Posted by Bean

Correct. Rog is a bloviating idiot.

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That's one view I suppose. The hope for a stabilizing rain event is a hope in vain.

There are no right or wrong answers here.

My one consideration is the shallow, relatively warm snow pack that contained quite a bit of H2o vapor and a lot of latent heat/energy being suddenly blanketed by 12-18" of snow and then subjected to what looks to be a week of extremely cold temps. Daytime high today at 9400' is -6F.

Seems like a recipe for a terrible basal layer that will get buried when it warms up and snows again and will haunt us for the entire year.

Then again, maybe it will rain.:wink:

Had there been a hard freeze before the first big snow?

Here in NM, there wasn't, and the first four or so inches is very "sugary" right now. (pretty sure that's not a term of art, but I'm taking a refresher course soon).

Just about 2-3 hours ago, we started getting high winds (gusts to ~65mph).

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Originally Posted by hortence

Had there been a hard freeze before the first big snow?

Here in NM, there wasn't, and the first four or so inches is very "sugary" right now. (pretty sure that's not a term of art, but I'm taking a refresher course soon).

Just about 2-3 hours ago, we started getting high winds (gusts to ~65mph).

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This is in SW Montana, 35 miles Nnw of YNP.

We had a somewhat mild fall but the ground was well frozen by the time we started accumulating snow. Sugary snow just above the ground surface (Facets or Hoar) is a fact of life in this region and your terminology is correct.

Keep in mind the ground is a nearly constant 0 deg. C or 32 deg. F during the winter.

little bit west of you, well a couple mtn. ranges west, the cascades are having a difficult time getting into the maritime rhythm. little snow followed by multiple cold high pressure system days then a big wind rain snow event that deposited inches to feet depending on which side of 6,000' you were standing at, followed by another cold dry high pressure dominant week.
ullr shaking shit up
b

I think we are stuck in a broadly similar pattern here in the Wasatch. On sunny aspects below 8000' or so, we entered this most recent storm with nearly-bare ground. Northerly aspects at all elevations were rotten facets to the ground. I saw enormous surface hoar growth in the sorts of places one would normally suspect it.

Now, we are seeing single-digit highs with a 40" give-or-take snowpack around the resorts. The new snow will turn to rotten facets just like the old stuff unless we get a change of pace.

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Originally Posted by neufox47

Me thinks not in a continental snow pack, I think it would get worse with the cold he's talking about.

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maybe not so much if there's no new load to crush the chips. time heals what's there to a point, especially if temps stay constant. but if a new load comes you better hope it's many feet with a shit ton of weight to maybe take care of things on all but maybe not north aspects. or better yet, wait for the summer snowpack:)

continental and summer go better together.

rog

hrmph.
Freezing levels went to 2000m with precip. winds shifted from N to S back to N so variable slabs are probable... total sufferfest to get to treeline and beyond where the skiing may be ok if it wasn't for the wind. Maybe I will ski on saturday... or I might just go for a skin then hack a chunk of crust off an throw it in a couple fingers of scotch and contemplate boot packing down. -20C before wind chill may temper my aspirations.

Rideit where did you get that quote from Z?

And Bunion this reminds me of the "Resetting the Snowpack" deal we did a few years ago. We have a similar deal down here. Most consistent and frightening weak layer interface is crust/ facets about 10 cm above the ground, mostly north. Now overlain with settled wind slab and new faceting due to cold snow. Takes a lot to break it, but goes clean and fast- sp, as they say in Canadia. So- a persistent to deep slab problem I am gonna worry about for a while.

Then the E and SE have wind issues- hard slab breaking on connection with drought surface would be my worry. West- hmmm. Not a clue.

Hope you are well stay in touch
salsa

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Originally Posted by Bunion

In SW Montana we have had a relatively shallow snow pack again this fall. Lots of facets and lots of sun crusts.

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This sounds much like home :)

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Originally Posted by Bunion

Until yesterday;

Some periods of colder weather followed by milder weather. All last week until mid day yesterday has been mild. At and above 7K during the days: 32F+ with lows in the teens and 20s most nights, mostly clear skies during the day and night.

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I'm not going to look up what the weird non-metric numbers are, but I would expect that this time of year surface hoar will form if the weather is clear and calm for several days/nights, even with comparatively mild temperatures.

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Originally Posted by Bunion

Things changed yesterday as a moist parcel of air began to move into the region beginning as snow above 7K and rain in the valley. Late afternoon the skies opened and it snowed pretty good. The remote stations are showing 4-6" overnight, around 12" in the past 24 hrs. Temps have dropped off the table and it is now -10F and still going down. Forecast temps could reach -25 or lower through the weekend.

What do folks think this will do to the underlying snow pack?

How about the new snow?

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I think the surface hoar would be mostly destroyed in this case since it rained at the beginning of the precip event, also if snow was very wet and heavy. However, going from warm beginning to cold snowfall later on, I would expect a thin freeze crust to form either at the old/new interface or within the new snow, depending on when the temperature drop occured. (Very cold snow on warm-ish, wet-ish old snow would cause freezing of liquid water in wetter/warmer snow.) This wouldn't be a major layer of ice easy to find in a pit but it would be enough to mess things up. Freeze crust will act as a vapour barrier so give it a little time (~day) and you will get a layer of hoar below the freeze crust, i.e. either on the old snow, in the new snow, or both. Voilá!

Salsa, it was on a FB post from him.

^^^^^^^doosh.

Rog

Who?
Me or Z?

(Hah...I know the answer!)

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Originally Posted by rideit

Who?
Me or Z?

(Hah...I know the answer!)

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think long and hard:)

rog

Ok!
And while smoke is pouring out of my ears, tell us more about the '72 hour safety' rule regarding this season's snowpack!