24-25

Upper Brackett Creek

Date

Sun, 12/29/2024 - 14:10

Activity

Skiing

Dug at 7000ft up Brackett Creek near but well below Texas Meadow. HS82 with mid pack weak(er) layers that produced propagation in an extended column test (ECTP13) at around 45cm down. Snowing steadily in the afternoon with no wind at this mid elevation.

Region

Bridger Range

Location (from list)

Brackett Creek

Observer Name

Christopher Pruden

Read more about 1cm ice crust

Thick and robust ice crust layer widespread above white elephant. Photo: Ride Rasmussen Style

Island Park, 2024-12-29

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Snowing and Blowing - Cooke City

Date

Sun, 12/29/2024 - 13:00

Activity

Skiing

This is avalanche weather - heavy snowfall and strong winds transporting snow. With this weather, it doesn't really matter what's going on in the snowpack. The loading from snowfall and strong winds will find the weakest layer in the snowpack and produce persistent slab avalanches.

Snow depths going up from Republic Creek at 8200 ft to the top of Woody Ridge at ~10,000 ft ranged from 60 cm to 120 cm. Weaker where thinner and stronger where deeper. What surprised me was that we couldn't get a single collapse/whumpf or any cracking despite our best efforts getting off the established skin track. Given the rapid loading and wind loading combined with buried facets, I expected at least on collapse. However, a lack of collapsing doesn't override all the other red flags.

The snowpack north of town and south of town seemed reasonably similiar. The biggest differences were with elevation. Generally above maybe 9000-9500 ft, the snowpack is a goof 4 feet deep.

I WON'T BE SURPRISED TO HEAR OF SOME LARGE AVALANCHES AT UPPER ELEVATIONS on peaks like Henderson, Crown Butte, etc where some slopes are being heavily wind-loaded.

Looking into the future, though, I feel optimistic. The snowpack is growing and will hopefully get stronger in the future as weak layers are insulated and buried more deeply. Yesterday north of Cooke, weak layers generally buried about 2 feet deep showed signs that they were gaining some strength and hardness. We'll see.

Region

Cooke City

Location (from list)

Woody Ridge

Observer Name

Staples

Divide Peak Ski

Date

Sun, 12/29/2024 - 15:00

Activity

Skiing

Moderate SW'ly winds on the ridge were enough to entrain and transport some surface snow. However, windslab formation was very isolated, slabs were soft (4F), and not reactive to ski travel. Most surface snow in the area was unconsolidated, in some cases with a thin (<1cm) surface wind skin.

The top 150 feet of the SE path was scoured with variable ski quality, however below this the snow was largely unaffected by today's wind and skied well. No tracks were visible from previous days.

Around 2pm the base of the clouds descended, and snowfall began at a rate of S-1.

Region

Northern Gallatin

Location (from list)

Divide Peak

Observer Name

N. de Leeuw

Cooke City Area North

Date

Sat, 12/28/2024 - 14:35

Activity

Snowmobiling

We rode around a big chunk of the Cooke City area from the Miller Road, up to Daisy, around the backside of Fisher Mtn, into Fisher Creek, and looping around Scotch Bonnet Mtn. Ee saw no signs of instability. No cracking or collapsing. While tracks on slopes don't indicate stability, there were a lot of tracks on small test slopes, and none produced small avalanches.

In all our snowpits, the weak layers were generally 2-2.5 feet deep and I was pleasantly surprised that they seem to be gaining some hardness. It feels that the snowpack has benefited from the steady trickle of light snow in the Cooke area. It hasn't added much water weight, but the continuous light snowfall in the Cooke Area has been slowly insulating and burying the weak layers without stressing them.

Unfortunately, we could not find any buried surface hoar, but we know it's out there. We also know that other areas like slopes south of town up Republic Creek are likely much weaker.

Without a major load of snow (and water), below treeline, avalanches are still possible but don't feel too imminent. It's different story going above treeline - where avalanches have been happening, where there's lots of wind loading, and where there are lots of potential trigger points. Stay below treeline.

Region

Cooke City

Location (from list)

Scotch Bonnet

Observer Name

Staples

Storm Slab weak layer

Date

Sat, 12/28/2024 - 14:30

Activity

Snowmobiling

Riding in the vicinity of Fish Creek Trail. Conducted a snowpit, result, ECTX. Snow was stable in this particular spot, did not have enough time to conduct another snowpit. HS 115, melt freeze crust 6-8" below surface, SH at 75cm, facets approximate lower 1/3 snowpack, 2-3 melt freeze crusts in snowpack. Overall 2 cohesive slabs make up the snowpack in this particular snowpit, split by MFcr. Also in the area signs of wind slabs on N, NE, E, and SE aspects. Airtemp -6C, moderate winds from SW, light snow, and OVC.

Region

Island Park

Location (from list)

Black Canyon

Observer Name

Ride Rasmussen Style

Storm snow density increasing

Date

Sun, 12/29/2024 - 15:50

Likely the same up high, at the house on Horse Butte the storm snow has been increasing in density dramatically since morning.

Observer Name

Cimonetti

poor activity on snow obs list

Date

Sun, 12/29/2024 - 10:20

testing snow observations form

Region

Bridger Range

Observer Name

Jim Earl

Ice Crust layer by White Elephant

Date

Sun, 12/29/2024 - 13:30

Activity

Snowmobiling

Thick and robust ice crust layer widespread above white elephant. Currently 4-5” of fresh snow on top of crust. Currently snowing heavily with moderate winds SW with gusts.

Region

Island Park

Location (from list)

Yale Creek

Observer Name

Ride Rasmussen Style

GNFAC Avalanche Forecast for Sun Dec 29, 2024

Snowpack and Avalanche Discussion

Intense snowfall with moderate wind will create dangerous avalanche conditions, and large human-triggered avalanches are likely. Snow stability will get worse through the day, especially on wind loaded slopes where natural avalanches are likely during the storm.

The snowpack has weak layers of sugary facets and surface hoar buried 1-3’ deep which showed signs of instability over the last couple days, including a <a href="https://www.mtavalanche.com/node/32662"><span… report</a> of a snowmobile triggered avalanche that partially buried a rider near Lionhead (<a href="https://www.youtube.com/watch?v=01zVyy8U8D8&list=PLXu5151nmAvToI_ir… video</a>, <a href="https://youtu.be/4xSA_C9cPuc?feature=shared">… Park video</a>, <a href="https://www.youtube.com/watch?v=FKh0OZ-BnUs">… Rind video</a>). Persistent slab avalanches breaking on this weak layer can break hundreds of feet wide and can be triggered from lower angle terrain connected to slopes steeper than 30 degrees.

Choose terrain that is less than 30 degrees steep, and not connected to or below anything steeper. Be extra cautious of steep wind-loaded slopes, and avoid crossing or sitting in runout zones below. The avalanche danger is HIGH on wind-loaded slopes and CONSIDERABLE on all other slopes near Island Park, West Yellowstone and in the southern Madison and Gallatin Ranges.

Heavy snowfall and moderate wind will cause the avalanche danger to rise through the day. A person can trigger wind slab avalanches that easily break within fresh drifts that form today. These can be large enough to bury a person, especially near Cooke City where more snow has fallen over the last week (18” = 1.8”SWE) and more is expected today.

Additionally, persistent slab avalanches could break deeper on weak layers buried 1-3’ deep. While there has been less signs of instability recently in these areas, snowfall has been slowly adding weight over the last week, and today’s intense snowfall and wind could finally overload the strength of these weak layers (<a href="https://www.youtube.com/watch?v=P6thCGML-1s&list=PLXu5151nmAvToI_ir… City video</a>, <a href="https://www.youtube.com/watch?v=yuTTHqltBiw">… video</a>, <a href="https://www.mtavalanche.com/node/32650"><span… media and observation</a>). Avalanches on persistent weak layers are less predictable, and can break after multiple people cross a slope, and without obvious signs of instability. If you have any doubt about snowpack stability, steer clear of steep slopes and runout zones below.

Practice conservative decision making today, and choose routes that avoid wind-loaded slopes steeper than 30 degrees. Human triggered avalanches are likely, especially on wind-loaded slopes, and the avalanche danger is CONSIDERABLE near Bozeman, Big Sky and Cooke City.

Read more about GNFAC Avalanche Forecast for Sun Dec 29, 2024

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