24-25

Triggering avalanches in Hyalite

Date
Activity
Ice Climbing

At the base of G2 I triggered a 3 inch x 100 foot soft slab. I was surprised how far it propagated. It looked like it failed on a density change under the morning's new snow. 40 feet up on the first large bench we triggered another slide, 6 inches deep, the entire width of the bench. It could have pushed a climber off if they were in the middle of it. It was snowing steady (1"/hr) and wind was minimal, but a few hours later we could see plumes higher up in the gullies.

It had such zip to the propagation that I'm thinking it might take a day for it to not be reactive. There was no way we wanted to get on anything open and steep. 

Region
Northern Gallatin
Location (from list)
Hyalite - main fork
Observer Name
Doug Chabot

GNFAC Avalanche Forecast for Fri Feb 7, 2025

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>It’s been a wild week of unusual weather - with hurricane force winds, winds blowing from unusual directions, both very warm and very cold temperatures (sometimes right next to each other with crazy strong temperature inversions), and periods of rapid snowfall. This all came after some new weak layers formed and it has left us with quite a variable snowpack.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Now it’s snowing again. This will both add load to the snowpack and make it harder to visually identify what’s been going at the snow surface over the last week (</span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=pwAambVPOeg"><span><span><span><span><s…’s video</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> from Blackmore yesterday).</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Unusual weather leads to unusual avalanches. This has certainly been the case over the last couple days.&nbsp;</span></span></span></span></span></span></p>

<ul>
<li><span><span><span><span><span><span>On Wednesday, Big Sky Ski Patrol intentionally triggered an avalanche with explosives on a&nbsp; slope loaded by the strong south winds that broke up to 7 feet deep, breaking on the old snow surface from dry weather in late January. They haven’t seen an avalanche like that on that slope in 40-50 years. (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34027"><span><span><span><span><span><…;, </span></span></span></span></span></span><a href="https://www.kbzk.com/news/local-news/avalanche-triggered-during-mitigat… story</span></span></u></span></span></span></span></span></a></li>
<li><span><span><span><span><span><span>Also on Wednesday, skiers triggered many storm slab avalanches in the new snow at low elevations on </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34015"><span><span><span><span><span><…. Ellis</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span> and in the </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34013"><span><span><span><span><span><… Range</span></span></u></span></span></span></span></span></a><span><span><span><span><span><span>.</span></span></span></span></span></span></li>
<li><span><span><span><span><span><span>There have also been plenty more typical avalanches on wind-loaded slopes below ridgelines across the advisory area (examples from near Cooke City (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/avalanche-north-crown-butte"><spa…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/scotch-bonnet-north-avalanche"><s…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/natural-avalanche-mt-henderson-ne…;, </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/natural-avalanche-miller-ridge-ne…;), </span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/33978"><span><span><span><span><span><…;, and the </span></span></span></span></span></span><a href="https://www.mtavalanche.com/images/25/wind-slab-crown-hourglass-couloir…;).</span></span></span></span></span></span></li>
</ul>

<p><span><span><span><span><span><span>Very strong winds and winds from unusual directions (out of the east) have loaded slopes that aren’t usually loaded, so be on alert for wind loading everywhere. Additionally, be on alert for slides on lower elevation slopes that usually aren’t much of a concern. In some cases, with the strong inversions mid-week,&nbsp; they may have touchier conditions than higher elevation slopes (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/34031"><span><span><span><span><span><…;).&nbsp;</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>With lots going on in the snowpack and it being loaded again, avalanche conditions are dangerous and cautious route-finding is required. Avalanches could break as </span></span></span></span></span></span><span><span><span><strong><span><span>Wind Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> either in the new snow or from snow drifted earlier in the week, </span></span></span></span></span></span><span><span><span><strong><span><span>Storm Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> as snow piles up during intense precipitation today, or</span></span></span></span></span></span><span><span><span><strong><span><span> Persistent Slabs</span></span></strong></span></span></span><span><span><span><span><span><span> on the weak layers that formed during the dry period in late January.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Today, the avalanche danger is CONSIDERABLE.</span></span></span></span></span></span></p>

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Poor Test Scores on Mt. Ellis

Date
Activity
Skiing

Dug on a NE aspect at about 7800’ on Mt. Ellis. Noticed pretty significant wind loading/cornice development from yesterday and was easily able to get small cornices to break off. Most notable test result was ECTP16 down 35 cm on a layer of surface hoar. Besides the concerning surface hoar layer the snowpack was generally right side up and seemed pretty solid. Photo of pit profile attached. 

Region
Northern Gallatin
Location (from list)
Mt Ellis
Observer Name
Eric Heiman

Several Older Wind Slab Avalanches on Blackmore

Mt Blackmore
Northern Gallatin
Code
SS-N-R2-D1.5-S
Elevation
9600
Aspect
E
Latitude
45.44440
Longitude
-111.00400
Notes

The wind had hammered snow surfaces at all elevations above tree line on Mount Blackmore. There was evidence of several R1-2/ D1-2 wind slab avalanches that likely ran this weekend on the east face of Blackmore.

Number of slides
3
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
1.5
Bed Surface
S - Avalanche released within new snow
Problem Type
Wind Slab
Vertical Fall
400ft
Slab Width
75.00ft
Snow Observation Source
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year