22-23

Wind-drifting

Date

Tue, 12/27/2022 - 12:45

Activity

Skiing

We skied the west slope of Woody ridge today.. At 9814', there was 200 cm height of snow. The was 300° azimuth. Slope was 25°. Air temp was 28°. Wind was steady 5 mph, with gusts at least 13 mph.

Temp at the dump parking lot was 36° at 0930, and my skins continued sticking up to almost 9000'.

Don and Jesse skied the same run yesterday, to 10,000' and there was deeper ski penetration yesterday (boot deep), and the snow today had settled, so ski penetration was only 2-3". In addition, yesterday's tracks had drifted completely in. Our skin tracks today filled in rapidly, due to steady snow and blowing wind.

There was no whumphing or cracking either day. Don says he noticed "hollowness" yesterday above 9800'.

We found a lot of wind-affected snow the face, especially closest to a gully on the side. From 9200' up, there's probably 2-4' of wind deposition.

Region

Cooke City

Location (from list)

Woody Ridge

Observer Name

Traute Parrie

Read more about Avalanche in Sage Basin 2

Natural avalanche in Sage Basin. Appear to have broken on a layer of facets underneath the new snow. Photo taken 12/28/22. Likely occurred early morning or overnight. Photo: GNFAC

Forecast link: GNFAC Avalanche Forecast for Thu Dec 29, 2022

Southern Madison, 2022-12-28

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Read more about Avalanche in Sage Basin 1

Natural avalanche in Sage Basin. Appear to have broken on a layer of facets underneath the new snow. Photo taken 12/28/22. Likely occurred early morning or overnight. Photo: GNFAC

Forecast link: GNFAC Avalanche Forecast for Fri Dec 30, 2022 GNFAC Avalanche Forecast for Sat Dec 31, 2022

Southern Madison, 2022-12-28

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Divide Peak snowpack

Date

Wed, 12/28/2022 - 10:55

Activity

Skiing

I toured up toward Divide today, mostly just to get out and take a peek at the snowpack. The storm overnight dropped 10-20 cm up high, and it was getting moved around a fair amount by the wind.

I dug my first pit on an east aspect at 8900’. The snow was 165 cm deep here, and there was a visible dark band 20 cm down that was pencil-hard and 1 cm thick. I got an ECTN13 on this, failing on a thin layer of facets just below the harder snow. I also got an ECTN 17 on another thin layer of facets another 20 cm down. When I filled the pit in, the top 20cm readily came off of my extended column, and the rest stayed cohesive to the ground as I tipped it over, save for the rotten stuff at the very bottom of the snowpack.

I dug another pit at 9550’ on the SE aspect of Divide. This one was 145 cm deep and had a similar structure to my first one, and gave me ECTN14 and ECTN18 on what I believe to be the same layers, although the firm band of snow 25 cm down didn’t have as obvious of a layer of low-density facets beneath it. I did get a clean, fast propagation 60 cm down at ECTP22. The slope I was on was only 28 degrees, but I bailed to head home and eat cheesecake instead.

Region

Northern Gallatin

Location (from list)

Divide Peak

Observer Name

Sam Reinsel

GNFAC Avalanche Forecast for Wed Dec 28, 2022

Snowpack and Avalanche Discussion

The Lionhead and Island Park mountains have dangerous avalanche conditions. 6-9” of heavy, wet, dense snow at <a href="https://www.mtavalanche.com/weather/wx-avalanche-log"><span… sites</a> equaled 1.2”-1.6” of <a href="http://snow.wyo.gov/snow-surveys/snow-water-equivalent-swe"><span… water equivalent (SWE)</a>. Trust me…this is a lot of weight. There is a weak layer of sugary, faceted snow about 1-2 feet under the surface which will avalanche. Our <a href="https://youtu.be/F8HKebJ_OJA">… from Lionhead</a> and this <a href="https://www.mtavalanche.com/images/22/new-weak-layer-lionhead"><s…; show the problem causing this warning. Stay away from avalanche terrain. This includes underneath steep slopes and drainage bottoms which are terrain traps. For today, the avalanche danger is rated HIGH on all slopes.

The southern Madison Range, southern Gallatin Range and mountains around Cooke City all received 4-6” of snow equaling 1.1” of <a href="http://snow.wyo.gov/snow-surveys/snow-water-equivalent-swe"><span…; with very strong SW wind gusting to 60 mph. This snow fell onto a snowpack with a known weak layer of sugary facets buried 1-2 feet under the surface. This layer is not everywhere, but the avalanche potential will be elevated on slopes harboring it. Dave and I found it in Bacon Rind yesterday and on one slope it was remarkably unstable (<a href="https://www.mtavalanche.com/node/27364"><span… and video</a>). In Cooke City a snowboarder triggered a slide on Monday (<a href="https://www.mtavalanche.com/node/27341"><span… and photos</a>), and a skier found this weak layer south of town on 2 occasions (<a href="https://www.mtavalanche.com/node/27365"><span…;). Another weak layer of faceted snow is near the ground which warrants caution because any slide breaking this deep will be large. Given yesterday’s new, dense snow and strong wind, it’s a good idea to not get into avalanche terrain. Be especially careful at the bottom of slopes because these areas seem safe, but are not. Avalanches can be triggered low on a slope when the weak layer is connected to higher elevations. For today, the avalanche danger is rated CONSIDERABLE on all slopes since human triggered avalanches are likely.

Rain, dense snow and strong wind plagued the mountains around Bozeman and Big Sky yesterday. 2-3” of new snow equaled .4-.6” of <a href="http://snow.wyo.gov/snow-surveys/snow-water-equivalent-swe"><span…;, or 20% snow density, which gave the snow a cream cheese consistency. These mountains have 2 weak layers of sugary, faceted snow on many, but not all slopes. These can be found 1-foot under the surface and the bottom third of the snowpack. New snow, especially on wind-loaded slopes, is keeping the possibility of triggering avalanches alive. On Monday, a skier triggered a collapse or “whumpf” of the snowpack near Big Sky (<a href="https://www.mtavalanche.com/node/27334"><span…;), Dave found weak snow on Mt. Blackmore (<a href="https://youtu.be/jjrqrzYhpIc">…;), and Alex also found weak layers and recent avalanches on Buck Ridge (<a href="https://www.youtube.com/watch?v=C2HXtmgNkt8">…;). The only way to know if these weak layers are present is to dig and assess. For today, the avalanche danger is rated MODERATE on all slopes.

Please share avalanche, snowpack or weather observations via our<a href="https://www.mtavalanche.com/node/add/snow_obs">…; website</a>, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).

Read more about GNFAC Avalanche Forecast for Wed Dec 28, 2022

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out: Events and Education Calendar.

Weather and Avalanche Log for Wed Dec 28, 2022

Read more about Weather and Avalanche Log for Wed Dec 28, 2022

AVALANCHE WARNING West Yellowstone and Island Park

Reactive Layer Still Present Higher Up

Date

Tue, 12/27/2022 - 14:15

Activity

Snowboarding

Pit Location: E / ESE Aspect | 10,000' | 220 - 230 cm snow depth | Near Treeline | 28 degree slope

Weather at 14:15: OVC | S1 | Winds Strong out of the S / SSW

Test Results:

16cm down from surface; ECTN2 PC and ECTN3 PC at the newer snow interface, still a fairly soft slab without a lot of cohesion in this particular area

71cm down from surface; ECTP21 SP and ECTP23 SP, broke on the same layer of small facets (~0.5-1.0mm) noted in 12/27 forecast below this week's more recent storm snow

Mostly minor cracking observed at the snow surface during today's outing, a couple of shooting cracks were observed in steeper wind drifted snow in more exposed areas

Region

Cooke City

Location (from list)

Woody Ridge

Observer Name

M Bortnowski

Finding weak snow

Date

Tue, 12/27/2022 - 10:30

Activity

Skiing

We parked at the bridge and headed up from there. We dug our first pit on a south facing mid-elevation hill. There was 75 cm of snow (HS) a 5 cm thick faceted layer 1 foot deep, then solid snow to the ground. The facets are the same we are finding elsewhere and I got a CT0, which denotes instability. We went to the upper meadow and dug 2 pits (125 and 100 cm HS) but this same faceted layer was thin and not reactive. Neither were the facets in the lower third of the pit. We went to the Skillet and dug there. Again the upper faceted layer was thin and not an issue. The CT0 has me concerned and I am ruling the ECTNs as being irrelevant.

Region

Southern Madison

Location (from list)

Bacon Rind

Observer Name

Doug Chabot

Dense powder and some facets

Date

Tue, 12/27/2022 - 12:45

Activity

Skiing

Dug and skied in a protected, treed little bowl I visit at 9500 ft. with a general ENE aspect. The approach is on a solar aspect with minor avalanche terrain between 8-9K. The quick n dirty pit was about 130 cm, ENE, 9300ft., just off ridge top. Bottom half was faceted, 2mm generally, but surprisingly tightly packed together. Hardness of 1F in much of the faceted section, with a couple of layers of 4F. Upper half of the pack was generally rounds until near the surface where it was a bit more faceted. We got a CT6 Q2 on a wind slab interfaced with other wind slabs about 30 cm's down. The deeper pack did not fail in CT. The unstable result near the surface did not scare me particularly due to the nature of the terrain, isolated nature of the wind slab confined to the very top of the ridge, ability to safely cut entrances to runs, relatively thick timber, etc. We skied dense powder with no signs of instability beyond the snowpit; all about terrain choice yesterday (every day?).

Region

Northern Madison

Observer Name

Mike Buotte