24-25

We rode out to Lulu Pass to look at the few avalanches that were reported yesterday on Henderson and Fisher Mtn. Today we did not see any avalanches that weren't previously reported, other than one small, but thick wind slab on south facing slope of Scotch Bonnet (photo). At least the avalanche on Fisher and one on Henderson broke near the ground (pics attached). Some slides were heavily refilled by drifted snow, so it was hard to tell how deep they broke.

Yesterday I saw a wide slab avalanche up on west Woody Ridge from town (photo attached). It happened late on Wednesday or overnight during or after the strong winds and snowfall.

We dug a pit on a north-northeast facing slope below Fisher Mtn. (on Rob's Knob). Snowpack was just over 3 feet deep with a stripe of surface hoar in the middle. Generally 1F to Pencil hard slab above the SH. Facets near the ground were 2-3mm and rounding. We had ECTP22 on the surface hoar and ECTN22 and PST 25/100arr.

Despite the generally hard and rounded facets near the ground, recent avalanches are a sign that those are a problem in addition to the surface hoar.

Clear and mostly calm today. A few rollerballs on southwest aspects.

Overall, the recent avalanche activity is a sign that the early season weak layers are a problem to watch going forward. Danger and likelihood of avalanches may decrease in the immediate future with a break from loading, but we need to be thinking about these layers when future storms add up.

Region

Cooke City

Location (from list)

Fisher Mtn.

Observer Name

Alex Marienthal

Recent large avalanches near Cooke City - 20 Dec 2024

Read more about Recent large avalanches near Cooke City - 20 Dec 2024

Read more about Risky business in the Bridgers

Dug a pit at 7600 ft on a NE facing slope. Full propagation on isolation of the column on the layer of concern about 16 inches down in this zone. Photo: Anonymous

Bridger Range, 2024-12-20

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Risky business in the Bridgers

Date

Fri, 12/20/2024 - 11:50

Activity

Skiing

Went out to have a look in the northern Bridgers today, hopeful that the moderate rating for the Bridgers today would lead to some fun lowish angle action.
Dug a pit at 7600 ft on a NE facing slope. Full propagation on isolation of the column on the layer of concern about 16 inches down in this zone. Went a little higher up and got a big whumpf and that was all I needed to bail on even the lower slopes.

Region

Bridger Range

Location (from list)

Northern Bridgers

Moist snowpack in Hyalite

Date

Fri, 12/20/2024 - 11:00

Activity

Skiing

Light winds and a sunny morning were quickly having an effect on the snowpack at history rock. Around 40f temps all day, with a moist, gloppy, snow surface. A quick dig in the top meadow showed the storm/windblown snow was moist down to the crust formed during our last high pressure, and the basal facets were also moist up to around 30cm from the ground. We saw no signs of instability in the less skied areas of the top meadow, including those that had been recently wind loaded.

Region

Northern Gallatin

Location (from list)

History Rock

Observer Name

Wyatt Hubbard

GNFAC Avalanche Forecast for Fri Dec 20, 2024

Snowpack and Avalanche Discussion

Triggering, large, dangerous avalanches remains likely today on slopes steeper than 30 degrees.

The reports continue to flow in of avalanches that broke during the snow and wind events this week. New reports yesterday include:

<ul>
<li>Many natural avalanches near Cooke City, in the <a href="https://www.mtavalanche.com/node/32550"><…, Fischer and Sheep Creek drainages</a> and another in <a href="https://www.mtavalanche.com/node/32573"><… Goose Lake area</a> that looks to have broken on the mid-pack weak layers. Both parties also reported numerous cracks/collapses while travelling yesterday.</li>
<li>A natural on <a href="https://www.mtavalanche.com/node/32576"><… Mountain</a>, near Big Sky and another on <a href="https://www.mtavalanche.com/node/32549"><… Peak</a>, in Hyalite.</li>
</ul>

There are widespread weak layers of sugary, faceted snow buried about 1-2 feet deep (videos from this week in <a href="https://www.youtube.com/watch?v=npOK4d94H50"><s… City</a>,<a href="https://www.youtube.com/watch?v=4xSA_C9cPuc"><s…; Island Park</a>, <a href="https://www.youtube.com/watch?v=RTUpUsNvXso"><s… Ridge</a>, and <a href="https://www.youtube.com/watch?v=w-aXzlPHrYA"><s…;). These weak layers formed on top of the snowpack during the dry weather in the first two weeks of December. Persistent slab avalanches have been breaking on these weak layers this week (<a href="https://www.mtavalanche.com/avalanche-activity"><span… activity log</a>). Faceted weak layers often remain easily triggered for a couple days after a loading event stops and we expect that to be true today. Slopes loaded or stiffened by the intense winds on Wednesday are likely to be the most easily triggered (with such intense winds, this will be many/most slopes).

Avalanche conditions will slowly improve, but we’re not there yet. The avalanche danger is CONSIDERABLE. For today - avoid slopes steeper than 30 degrees.

In the Bridger Range, triggering large avalanches is possible, but the weak layers are a bit stronger than elsewhere, so they won’t be quite as reactive. Yesterday, my partner and I found no signs of instability near the Throne, even while digging three pits to search for it, and felt comfortable tiptoeing into avalanche terrain (<a href="https://www.youtube.com/watch?v=pA-bcDkn6RQ">…;). I’m extra skeptical of slopes that got heavily wind loaded on Wednesday, particularly because of a natural on Saddle Peak that broke 1-3 feet deep, and ran 1500 vertical feet (<a href="https://www.mtavalanche.com/node/32548"><span…;).

If you want to get into steeper terrain, start off with smaller slopes, slopes just steeper than 30 degrees, and ones that have good runouts below this in case you get surprised. Watch for signs of instability (cracking, collapsing, or poor test results) and be ready to quickly retreat to lower angled slopes if you find them.

The avalanche danger is MODERATE in the Bridger Range.