20-21

Loose Dry Avalanches on the Throne

The Throne
Bridger Range
Code
L-N-R1-D1-I
Elevation
8000
Aspect Range
SE-NE
Latitude
45.88220
Longitude
-110.95200
Notes

Multiple small dry looses all across the throne. Sliding on a thin sun crust with overlying near surface facets buried 15-25 cms down. None stepped down to deeper layers.

Number caught
0
Number buried
0
Avalanche Type
Loose-snow avalanche
Trigger
Natural trigger
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Problem Type
Loose Dry
Slab Thickness
20.0 centimeters
Vertical Fall
500ft
Slab Width
50.00ft
Weak Layer Grain type
Near surface faceted particles
Weak Layer grain size
2.00mm
Weak Layer Hardness
F+
Slab Layer Grain Type
Decomposing and Fragmented precipitation particles
Slab Layer Grain Size
1.00mm
Slab Layer Hardness
F
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

GNFAC Avalanche Forecast for Tue Jan 26, 2021

Snowpack and Avalanche Discussion

<p>The mountains from the Lionhead Range through the Bridger Range received 1-3" of snow in the previous seven days and nothing in the last four. The lack of new snow provides the weak snowpack time to adjust and avalanches are becoming less likely. On Sunday, a snowmobiler triggered a wind-loaded slope in the Taylor Fork that piled debris 8 feet deep (<a href="https://mtavalanche.com/images/21/snowmobile-triggered-avalanche-sunlig…;). Yesterday, we did not see any other recent activity in the area, but we triggered a collapse and found a reactive layer of surface hoar buried 6-18" under the snow (<a href="https://www.youtube.com/watch?v=hkLoYCcemg0"><strong>video</strong></a&…;). Alex found similar conditions at Bacon Rind (<a href="https://www.youtube.com/watch?v=Sw_8eiygoSc"><strong>video</strong></a&…;). The weak depth hoar near the snowpack's base across all areas remains the most concerning weak layer. In the last week, we have reported avalanches, loud "whumphs" and unstable test results in the Madison, Gallatin, Lionhead and Bridger Ranges (<a href="https://mtavalanche.com/weather/wx-avalanche-log"><strong>weather and avalanche log</strong></a>, <a href="https://www.youtube.com/watch?v=HtHMcXwo3mw&amp;list=PLXu5151nmAvQDzKmH… video</strong></a>, <a href="https://youtu.be/fUK0nUTBSvU"><strong>Buck Ridge video</strong></a>). In the last two days and for the first time in a month, depth hoar in two of my snowpits did not propagate failure with extended column tests. This is a good sign, but keep the big picture in mind remembering that trust for this deeply buried sugary snow will be hard-earned.</p>

<p>Plan your route carefully and assess the snowpack thoroughly if you are considering entering avalanche terrain. Finding any sign of instability is a good reason to turn around and stick to low-angle terrain. Large, human-triggered avalanches remain possible and the danger is rated MODERATE.</p>

<p>Snowmobilers triggered several avalanches north of Cooke City three to four days ago on a layer of weak snow buried 12-18" deep. Yesterday, skiers recently witness a spiderweb of shooting cracks breaking on the same layer (<a href="https://mtavalanche.com/images/21/shooting-cracks-meridian-peak"><stron…;). Despite these events, stability is showing signs of improving. Currently, Doug is documenting these and other avalanches in the area (check out the <a href="https://mtavalanche.com/images/21/snomobiler-triggered-slide-near-huckl… photo</strong></a>, <a href="https://mtavalanche.com/images/21/cornice-triggered-avalanche-miller-ri… Ridge photo</strong></a>, <a href="https://mtavalanche.com/images/21/2-avalanches-sheep-mtn"><strong>Sheep Mountain photo</strong></a>). He found the suspect weak layer buried and it is adjusting to the weight on top (<a href="https://mtavalanche.com/images/21/surfae-hoar-crystalcloseup"><strong>p…;). A second weak layer of sugary snow is buried 2-3' deep on some slopes. This deeper layer is more prevalent in the thinner snowpacks around Cooke City and skiers recently triggered large collapses on this layer.</p>

<p>While tracks <em>don't equal</em> stability, riders are climbing steep slopes and are generally <em>not</em> triggering avalanches. A rider or skier can get unlucky and hit the "sweet spot" but the snowpack is less sensitive.&nbsp;Human-triggered avalanches remain possible and the danger is rated MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can submit them via our <a href="https://www.mtavalanche.com/node/add/snow_observation"><strong>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Upcoming Avalanche Education and Events

See our education calendar for an up-to-date list of all local classes. Here are a few select upcoming events and opportunities to check out:

Snowmobile Triggered Avalanche, Sunlight Basin

Taylor Fork
Southern Madison
Code
SS-AKu-R2-D2-O
Elevation
8800
Aspect
N
Latitude
44.96950
Longitude
-111.29200
Notes

A snowmobiler triggered an avalanche while side-hilling. No one caught or injured. The debris was estimated to be 8' deep. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowcat
Trigger Modifier
u-An unintentional release
R size
2
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Weak Layer Grain type
Depth Hoar
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year