21-22

GNFAC Avalanche Forecast for Wed Jan 26, 2022

Snowpack and Avalanche Discussion

<p>The arithmetic is basic: Wind + snow = wind slabs. 4-6” of snow that fell in Hyalite and Big Sky Monday night got blown into thicker drifts that can be triggered today. On slopes not affected by the wind it’s unlikely to trigger an avalanche. Ian and I were on <a href="https://www.mtavalanche.com/node/19525"><strong><u>Wheeler Mountain</u></strong></a> in the northern Gallatin Range yesterday and found sugary, faceted snow that would not support our weight when we stepped out of our skis (<a href="https://youtu.be/6ax6l1PhUb0"><strong><u>video</u></strong></a&gt;). We also found 6” of new snow that was likely blown into drifts last night. A skier on Divide Peak and the Big Sky Ski Patrol also reported fresh snow available for transport.&nbsp;</p>

<p>Wind drifts are most susceptible to triggering when they are new, like today. Shooting cracks are a sign that slabs of windblown snow can avalanche. Be wary near ridgetops. On slopes without wind loading it’s a good habit to dig and test before getting on steep terrain no matter the danger rating. For today the avalanche danger is rated MODERATE on wind loaded slopes and LOW on all others.</p>

<p>&nbsp;</p>

<p>The Bridger Range is windy, but lacks new snow to blow around. The southern mountains to West Yellowstone and Cooke City are calmer. Without new snow to load slopes or get blown into drifts the snowpack is generally stable and avalanches are unlikely. A buried weak layer of surface hoar is still lurking a foot or so under the surface in our southern mountains, but is not a serious concern…yet. It needs to get buried deeper, which may take a while given our paltry storms. Alex shows us this layer and reminds us to look&nbsp; for signs of instability like shooting cracks in his <a href="https://youtu.be/I6AleixLxTI"><strong><u>video from Taylor Fork</u></strong></a> this weekend. To avoid getting unlucky and finding a rogue instability, do a quick stability test before exposing yourself to serious terrain. For today the avalanche danger is rated LOW.&nbsp;</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><u>websi…;, email (<a href="mailto:mtavalanche@gmail.com"><strong><u>mtavalanche@gmail.com</u></str…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Upcoming Education Opportunities

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:

Skier Triggered Wind Slab, Mt Fox

Mt Fox
Cooke City
Code
SS-AS
Aspect
E
Latitude
45.12120
Longitude
-109.93000
Notes

Skier-triggered avalanche reported on Mt. Fox. Details unknown

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Natural Avalanche, Sheep Mountain

Sheep Mountain
Cooke City
Code
SS-N
Latitude
45.07220
Longitude
-109.92800
Notes

Natural avalanche reported on the east face of Sheep Mountain. Details unknown

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

GNFAC Avalanche Forecast for Tue Jan 25, 2022

Snowpack and Avalanche Discussion

<p>The Northern Gallatin Range was the snowfall winner yesterday with 6” of snow equal to 0.4” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… water equivalent</a> (SWE). The Southern Gallatin and Southern Madison Ranges and mountains around Cooke City got 2-3” equal to 0.1-0.2” SWE. The wind will pick up through the day and easily move this low-density snow into small drifts where human-triggered avalanches are possible. In the mountains around Cooke City and in the Southern Gallatin and Southern Madison Ranges there is a thin weak layer buried under one to two feet of snow on many slopes that may result in wider propagation of these wind slabs (<a href="https://www.youtube.com/watch?v=I6AleixLxTI&amp;list=PLXu5151nmAvT1nrM2…;, <a href="https://www.mtavalanche.com/images/22/surface-hoar-layer-s-madison-rang… </strong></a><a href="https://www.mtavalanche.com/images/22/surface-hoar-layer-s-madison-rang… surface hoar</strong></a>). A skier triggered avalanche late last week near Cooke City and one reportedly triggered on Sunday near Goose Lake illustrate the type and size of avalanche that are possible today (<a href="http://www.mtavalanche.com/node/25595"><strong>photo and details</strong></a>).</p>

<p>Avalanches breaking on deeper weak layers are unlikely so spend your time <a href="https://www.youtube.com/watch?v=sqn0KFZqXYs&amp;list=PLXu5151nmAvSpq8Ps… quick pits </strong></a>to test interfaces in the upper snowpack. If you observe propagating tests or see obvious signs of instability such as shooting cracks or recent avalanches, retreat to a different slope or move out of wind-loaded terrain. The danger is MODERATE on wind-loaded slopes and LOW on all others.</p>

<p>In the Lionhead area along with the Bridger and Northern Madison Ranges 2-3” of snow equal to 0.1-0.2” of SWE fell on a mostly stable snowpack. A weak layer of surface hoar is buried under 6” of light snow near West Yellowstone, but similar to areas without the weak layer, this is not enough to pose much of a hazard outside of technical or very steep terrain where a small avalanche could push you into or off obstacles. Over the weekend, the wind blew recent snow into relatively small, but unstable drifts in the northern ranges. On Saturday, a snowmobiler in the northern Bridger Range triggered a slide on a small slope (<a href="https://www.mtavalanche.com/images/22/snowmobile-triggered-wind-slab-sm…;) and on Sunday, a skier north of Bridger Bowl was caught and carried about 150’ in a small avalanche (<a href="https://mtavalanche.com/node/25615"><strong>details and photos</strong></a>). Thankfully, all parties involved were unharmed. Winds have been calm since then and these wind slabs have largely stabilized.</p>

<p>Today, avalanches are unlikely. Dig and test the upper snowpack and watch for signs of isolated instability such as cracking and expose only one person at a time to avalanche terrain. With mostly stable conditions, the danger is LOW.</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 Education Opportunities

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:

Human-triggered Avalanche, Playground

Playground
Bridger Range
Code
SS-ASu-R2-D1.5-I
Aspect
NE
Latitude
45.84260
Longitude
-110.92900
Notes

From Obs: "While skiing the playground, a northeast aspect in the Bridgers, my friends and I released a wind slab. The slab released on a rollover and was approximately 20 ft wide and 6-12" deep at the top. The slide carried my friend about 150 ft." 

Number of slides
1
Number caught
1
Number buried
0
Number killed
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
Trigger Modifier
u-An unintentional release
R size
2
D size
1.5
Bed Surface
I - Interface between new and old snow
Problem Type
Wind-Drifted Snow
Slab Thickness
12.0 inches
Vertical Fall
150ft
Slab Width
20.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year