19-20

GNFAC Avalanche Forecast for Sat Jan 11, 2020

Snowpack and Avalanche Discussion

<p>6 to 12” of low density new snow fell near Big Sky overnight. Moderate to strong southwest winds have built thick drifts on windloaded slopes. Snowfall totals have been variable across zone over the last three days &nbsp;– the greatest danger is in areas with the most new snow. If you find deep new snow and thick wind drifts, avoid all avalanche terrain. Avalanches can break under the new snow, or much deeper, including all the way to the ground (<strong><a href="https://www.mtavalanche.com/images/20/avalanche-ground-yc">photo</a></s…;, <strong><a href="https://www.youtube.com/watch?v=7vDe6LE-nhU&amp;list=PLXu5151nmAvSbcbVf…;). Human triggered avalanches are likely and the avalanche danger is CONSIDERABLE.</p>

<p>Triggering an avalanche is likely in Cooke City on any steep slope today. While the deep powder from this week’s storm is settling, weak layers deeper in the snowpack will take longer to heal from the large load they’ve received since New Year’s (40” of snow with 4” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… snow water equivalent</a>). Yesterday, riders near Daisy Pass saw a fresh snowmobile triggered avalanche on Chimney Rock and a larger natural avalanche that broke during the storm (<strong><a href="https://www.mtavalanche.com/images/20/snowmobile-triggered-slide-chimne…;, <strong><a href="https://www.mtavalanche.com/images/20/natural-avalanche-miller-mountain…;). Give these weak layers more time to adjust - stay off steep slopes today. Dangerous avalanche conditions exist and the avalanche danger is CONSIDERABLE.</p>

<p>With little new snow overnight, the wind drifted slabs that formed in the Bridger and Northern Gallatin Ranges over the previous several days will be harder to trigger today. However, caution is still merited. Yesterday, Dave got a dramatic test result near the Throne and decided to stick to lower angled terrain (<strong><a href="https://www.youtube.com/watch?v=WUM0Q69fPZE&amp;list=PLXu5151nmAvSbcbVf…;). Stay on alert for signs that wind drifts have remained unstable – cracks shooting out from your ski tips are a clear sign to find a lower angled or less windloaded slope. The avalanche danger is MODERATE today.</p>

<p>The mountains around West Yellowstone haven’t been seen much new snow this week. The snowpack is slowly adjusting and becoming less unstable (<strong><a href="https://www.youtube.com/watch?v=omt8Tt1rwms&amp;list=PLXu5151nmAvSbcbVf…;). However, there is widespread weak snow at the ground that remains worrisome. On Thursday, I remotely triggered a small slide (6” deep and 10’ wide) from 100’ away on a low elevation slope near Hebgen Lake(<strong><a href="https://www.mtavalanche.com/images/20/hebgan-lake-road-cut-avalanche-ja…;). Triggering larger slides remains possible. For today, the avalanche danger is rated MODERATE.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<strong><a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a></strong>, email us (<strong><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></strong&gt;), leave a VM at 406-587-6984, or Instagram (#gnfacobs).</p>

Webpage dedicated to the Centennial Range in Idaho and Montana

After the two snowmobiler avalanche fatalities on Reas Peak in the Centennial Range in January 2018 we created a webpage so riders could get good, relevant information regarding snowpack and avalanches.

YC Patrol triggered avalanche to ground

Yellowstone Club
Northern Madison
Code
SS-AE-R3-D2
Elevation
8500
Aspect
NE
Latitude
45.23110
Longitude
-111.44100
Notes

Yellowstone Club Ski Patrol triggered a slide with explosives, breaking at the ground, during avalanche mitigation work on Friday, 1/10/2020.

From Yellowstone Club Patrol: "It’s a NE facing slope at 8500’ ... got an avalanche to release on an old layer of well defined surface hoar (perhaps from mid-December). In some areas it stepped to ground. The crown was 2-4’ deep and the avalanche was recorded as R3/D2. The avalanche slid to the bottom of the runout and placed 3-12’ of snow in the road and completely blocked the road. This was a relatively large slide for this particular path this early in the season."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
An explosive thrown or placed on or under the snow surface by hand
R size
3
D size
2
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Snowmobile Triggered Slide on Chimney Rock

Daisy Pass
Cooke City
Code
SS-AM-R2-D2
Aspect
SW
Latitude
45.04970
Longitude
-109.96400
Notes

Snowmobile triggered avalanche on the WSW face of Chimney Rock near Daisy Pass. Likely triggered morning of 1/10/2020.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
R size
2
D size
2
Vertical Fall
200ft
Slab Width
75.00ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Natural Avalanche on Miller Ridge

Miller Ridge
Cooke City
Code
SS-N-R2-D2
Latitude
45.04230
Longitude
-109.96500
Notes

Natural avalanche on a steep east facing windloaded slope of Miller Ridge. Photo taken 1/10/2020. Likely broke Tuesday or Wednesday during the storm.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
2
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Snowmobile triggered avalanche on the WSW face of Chimney Rock near Daisy Pass. Appeared fresh on 1/10/2020. Photo: B. Zavora.

Cooke City, 2020-01-10

Windslab in Middle Basin

Middle Basin
Northern Madison
Code
SS-R1-D1
Latitude
45.33740
Longitude
-111.38100
Notes

Small windslab on the apron of the Buttcrack Chute in Middle Basin. Likely broke 1/9 or morning of 1/10/2020.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
R size
1
D size
1
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year