24-25 | Gallatin National Forest Avalanche Center

Wind slab in bridgers

Date

Sat, 01/04/2025 - 12:00

Activity

Skiing

Toured up the ramp this morning, found between 3-6” of new snow on the skin track, winds were fairly strong from the north/northwest and moving snow. Snow was falling heavily for the duration of the tour. As we made our last switchback in the ridge line meadow (8500ft directly east facing) near the top of the ramp, we triggered a wind slab. It propagated about 200 ft wide and was 3 ft at the deepest point. Interestingly on the edges and near the bottom (downhill side) of the slab it was only a few inches deep. It broke on the interface between the wind loaded snow and the light and dry snow we received a few days ago. When we entered the upper meadow there was no evidence of tracks from the day before. Further down the ramp we found cross loaded rolls that produced shooting cracks and collapses, and active snow loading from new snow and wind. A half hour later on our ski down, the skin track was partially buried by new snow as we exited the area.

Region

Bridger Range

Observer Name

Alex Shafer

Hebgen

Date

Sun, 01/05/2025 - 12:20

Activity

Skiing

Skied above hebgen today, and conditions were similar to what they were a couple days ago. An east facing pit at 8700’ had 85 cm of snow and failed on facets near the ground at ECTP 16. I ski cut a steeper slope and got no result, but my larger-volume partner was able to trigger a slide that broke 40-50’ wide and ran to the ground and through some trees. This was immediately adjacent to the fresh tracks of a very fortuitous skier and their pooch. Subjectively, it seemed like the basal facets had a bit more moisture in them today, but they are not strong yet.

Region

Lionhead Range

Location (from list)

Hebgen Lake

Observer Name

Sam Reinsel

Testing of AntiBot system

Date

Sun, 01/05/2025 - 09:00

Activity

Skiing

Seeing if the anti bot works ok.

Region

Northern Gallatin

Location (from list)

BRIDGER RANGE

GNFAC Avalanche Forecast for Sun Jan 5, 2025

Snowpack and Avalanche Discussion

Dangerous avalanche conditions exist and large human-triggered avalanches are likely. Yesterday on Lionhead Ridge near West Yellowstone, snowmobilers triggered a large persistent slab avalanche from flat terrain a safe distance away (<a href="https://www.mtavalanche.com/node/33332"><span… and details</a>), and another group reported a second similar sized avalanche nearby (<a href="https://www.mtavalanche.com/images/25/avalanche-airplane-bowl-lionhead"…;). Through the last week near Cooke City there were multiple large natural persistent slab avalanches that broke 3-4’+ deep (<a href="https://www.mtavalanche.com/node/33306"><span… Mtn.</a>, <a href="https://www.mtavalanche.com/node/33142"><span… Mountain</a>, <a href="https://www.mtavalanche.com/node/33267"><span… Peak</a>). These types of persistent slab avalanches are our biggest concern, due to the potential size and possibility to trigger from flatter terrain below or connected to steep slopes.

For nearly two weeks the mountains have received steady snowfall. This snow has gradually added weight and built thick slabs over weak layers now buried 2-4 feet deep. The gradual loading, and relatively minimal wind, has inhibited widespread avalanches all at once. However, over the last week we have seen avalanches almost daily as the snowpack reaches a breaking point on individual slopes at different times (<a href="https://www.mtavalanche.com/avalanche-activity"><stro… log</a>).

During yesterday’s snow, winds increased to moderate out of the northwest and west and drifted snow into thicker, stiffer slabs. These wind slabs, up to a foot deep, are possible to trigger today and make deeper avalanches more likely on wind-loaded slopes.

On Friday, snow fell as temperatures warmed which caused heavier snow to form slabs over lower density snow. Storm slab avalanches broke 8-10” deep within the “upside down” new snow on Friday (<a href="https://www.mtavalanche.com/node/33296"><span… observation</a>) and remained easy to trigger yesterday (<a href="https://www.mtavalanche.com/node/33335"><span…. Gallatin observation</a>). While new snow instabilities typically stabilize quickly, the recent observations of instability make it worth watching out for today. Cracking across the snow surface is a sign you could trigger slabs of new or wind-drifted snow.

Enjoy the new snow while staying on slopes less than 30 degrees, and away from flatter terrain below these steep slopes (<a href="https://www.youtube.com/watch?v=wez-MVpRq5w">…’s video</a>). Recent winds, new snow and buried weak layers make human-triggered avalanches likely today, and the avalanche danger is CONSIDERABLE.