22-23

Surface Hoar Buried 20cm (8-10") deep at Goose Lake

Date
Activity
Skiing

We rode through to the Goose Lake wilderness area boundary and skied from there to look at the snowpack in higher elevation, alpine terrain. Like the day before, we managed our exposure to avalanche terrain be keeping ourselves off and out from under large slide paths because of our concern for the possibility of deep slab avalanches. 

We dug two snowpits on the tour and found a layer of surface hoar buried 20 CM deep (on the far end of Goose Lake at ~10,000' elevation on an east and northeast-facing slope). It did not propagate in any of the tests we performed, but it is certainly something to watch for. We did not see it in our snowpits yesterday, it will take more time and more snowpits to pin down the extent of this new weak layer and whether it will become a widespread problem. 

Our two primary concerns for today were wind slabs, we observed several recent wind-slab avalanches on Mount Fox and Henderson Mountain, and deep-slabs like the one that caught a pair of riders on Thursday on the SW side of Henderson. 

Region
Cooke City
Location (from list)
Goose Lake
Observer Name
David Zinn

GNFAC Avalanche Forecast for Mon Mar 27, 2023

Snowpack and Avalanche Discussion

<p><span><span><span><span><span><span>Human-triggered avalanches are likely and natural avalanches are possible where new snow is drifted into denser slabs. Since Friday evening the mountains near Bozeman, Big Sky and West Yellowstone received 12-28” of snow equal to 0.9-1.8” of snow water equivalent (SWE), and we heard reports of 40” of low density snow in spots. Yesterday in the northern Gallatin Range, riders reported avalanches that broke up to a foot deep in the new snow (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28834"><span><span><span><strong><span… and details</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>), and skiers on Mt Ellis saw a recent skier triggered slide that broke up to 3 feet deep which was relatively large on a very small slope. This slide appeared to have partially buried a skier who self-extricated (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28823"><span><span><span><strong><span… and photos</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>).</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Avalanches breaking within the new and wind-drifted snow are most likely, but larger slides breaking several feet deep on old persistent weak layers are possible and have large consequences. </span></span></span></span></span></span><span><span><span><span><span><span>A slide that broke 8-10 ft deep earlier this week on Elephant Mtn. in Hyalite is an example of huge avalanches that could be triggered or break naturally today (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28785"><span><span><span><strong><span… and photos</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>). See our </span></span></span></span></span></span><a href="https://www.mtavalanche.com/avalanche-activity"><span><span><span><stro… activity list</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span> and </span></span></span></span></span></span><a href="https://www.youtube.com/playlist?list=PLXu5151nmAvTi1DBS5B4DBCruL1ULhkt… videos</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span> for more examples of recent big slides.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>You can reduce the risk of being caught in any type of avalanche by avoiding wind-loaded slopes steeper than 30 degrees. Choose small, simple terrain that is not exposed to trees, cliffs or confined gullies. Before traveling across or below any steep slope, carefully assess stability of the new snow and consider the possibility of deeper buried weak layers. If you suspect either could cause an avalanche, stick to slopes less than 30 degrees altogether. Avalanche danger is CONSIDERABLE on wind-loaded slopes and MODERATE on non-wind loaded slopes.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>In the mountains near Cooke City the main concern is triggering avalanches that break several feet deep on weak layers that were buried two months ago. On Thursday near Daisy Pass a snowmobiler triggered avalanche broke 4 feet deep, caught two riders, and one of them suffered a broken femur (</span></span></span></span></span></span><a href="https://www.mtavalanche.com/node/28785"><span><span><span><strong><span… and photos</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span>, </span></span></span></span></span></span><a href="https://www.facebook.com/100004284780258/videos/1424658804963632?idorva…;). Additionally, a person can trigger avalanches of recent wind-drifted snow. If you plan to travel on or below steep slopes, choose smaller slopes that have not been wind-loaded and do not have large consequences such as trees, gullies or cliffs below. See </span></span></span></span></span></span><a href="https://www.youtube.com/watch?v=nJWsF4g2Rjc&amp;lc=Ugz-FtvI57p9UyUzF3h4…’s video</span></span></u></span></strong></span></span></span></a><span><span><span><span><span><span> from yesterday in Cooke City for tips about terrain selection. </span></span></span></span></span></span><span><span><span><span><span><span>Human-triggered avalanches are possible and the avalanche danger is MODERATE.</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Please share avalanche, snowpack or weather observations via our website, email (mtavalanche@gmail.com), phone (406-587-6984), or Instagram (#gnfacobs).</span></span></span></span></span></span></p>

<p><span><span><span><span><span><span>Human-triggered avalanches are likely and natural avalanches are possible where new snow is drifted into denser slabs. Larger slides several feet deep on old weak layers are possible. Avoid wind-loaded slopes steeper than 30 degrees. Choose small, simple terrain that is not exposed to trees, cliffs or confined gullies. If you suspect buried weak layers or recent snow could cause an avalanche, stick to slopes less than 30 degrees altogether.</span></span></span></span></span></span></p>

Upcoming Avalanche Education and Events

Events and Education Calendar.

New snow avalanches at Portal Crk

Portal Creek
Northern Gallatin
Code
SS-N-R2-D2-S
Latitude
45.28900
Longitude
-111.14100
Notes

Saw a couple small natural slides breaking in the new snow. The one on the small slope beside the road actually appeared to have broken when a snow bike crossed the top just off the side of the road. The other was natural and occurred in the afternoon sometime 

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
2
Bed Surface
S - Avalanche released within new snow
Problem Type
New Snow
Slab Thickness
8.0 inches
Vertical Fall
350ft
Slab Width
200.00ft
Snow Observation Source
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

From obs 3/26/23: "Saw a couple small natural slides breaking in the new snow.... occurred in the afternoon sometime" Photo: J. Weingarten

Northern Gallatin, 2023-03-27

Terrain Choices are the key

Date
Activity
Skiing

We rode up to Daisy Pass, then back to Marty's. We skied up to the starting zone and found the thinner (100-150 cm deep) and weaker snowpack typical for this area. We found weak depth hoar near the ground and layers of surgery facets in the middle of the snowpack. This path slide 1.5 weeks ago, likely triggered by a rider. Four days ago a slide caught two riders and seriously injured one on the same aspect of West Henderson a mile from where we were. The snowpack structure was similar. The scary thing is Cooke right now is that avalanches are not happening on every slope or every day, but when they have occurred recently, they've been big.

We recommend either choosing terrain very unlikely to slide because it is less than 30 degrees and not underneath steep slopes, or choosing terrain that minimizes the consequences of getting caught - small slopes that don't have terrain traps like gullies, trees, rocks, or cliffs. And always, travel one at a time on the slopes while watching your partners from a safe spot.

We saw a smaller natural avalanche on Ray's while driving into town, north-facing slope, 2-3' deep, not very wide. This was the only recent avalanche we saw today, but the visibility was poor and we didn't cover much ground. 

Region
Cooke City
Location (from list)
Henderson Mountain
Observer Name
David Zinn

Surface snow breaking at Portal today

Date
Activity
Snowmobiling

Saw a couple small natural slides breaking in the new snow. The one on the small slope beside the road actually appeared to have broken when a snow bike crossed the top just off the side of the road. The other was natural and occurred in the afternoon sometime 

Region
Northern Gallatin
Location (from list)
Portal Creek
Observer Name
Jed Weingarten