19-20

From one of the riders that was caught, "The 3 persons involved were traveling across the slope about 20-30 yards up from the tree line parallel to the ridge line in the slide area when it broke, not high marking and not traveling uphill. One rider did increase his elevation while traveling across the slope but was never more than 1/4 of the way up when the slide was triggered."

Northern Madison, 2020-01-04

Bridger patrol triggered deep slab

Bridger Bowl
Bridger Range
Code
HS-ABc-R4-D3-O
Elevation
8500
Aspect
NE
Latitude
45.81560
Longitude
-110.92300
Notes

This slide was triggered by Bridger Bowl ski patrol during control work on Saturday (1/4/2020) on "The Drain". This is a heavily wind loaded slope on the south end of the ski area adjacent to the backcountry (Saddle Peak). It shows deeply buried persistent weak layers from early October and November were pushed to a breaking point by the recent snow and wind.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
An explosive detonated above the snow surface (air blast)
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
4
D size
3
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
48.0 inches
Vertical Fall
1000ft
Slab Width
100.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

This slide was triggered by Bridger Bowl ski patrol during control work on Saturday (1/4/2020). It shows deeply buried persistent weak layers from early October and November were pushed to a breaking point by the recent snow and wind. A person can trigger avalanches like this on heavily wind loaded slopes in the backcountry. Additionally, shallower large avalanches can be triggered on any steep slope. Photo: J. Olson

Bridger Range, 2020-01-04

This slide was triggered by Bridger Bowl ski patrol during control work on Saturday (1/4/2020). It shows deeply buried persistent weak layers from early October and November were pushed to a breaking point by the recent snow and wind. A person can trigger avalanches like this on heavily wind loaded slopes in the backcountry. Additionally, shallower large avalanches can be triggered on any steep slope. Photo: BBSP

Bridger Range, 2020-01-04

This slide was triggered by Bridger Bowl ski patrol during control work on Saturday (1/4/2020). It shows deeply buried persistent weak layers from early October and November were pushed to a breaking point by the recent snow and wind. A person can trigger avalanches like this on heavily wind loaded slopes in the backcountry. Additionally, shallower large avalanches can be triggered on any steep slope. Photo: BBSP

Bridger Range, 2020-01-04

Natural Avalanche on Yellow Mountain

Yellow Mountain
Northern Madison
Code
N-R2-D2
Elevation
9000
Aspect
SE
Latitude
45.29950
Longitude
-111.32000
Notes

A large avalanche crown was seen on Yellow Mountain from the Big Sky meadow village on the morning of 1/4/2020. It reportedly spanned across the entire avalanche path

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

GNFAC Avalanche Forecast for Sat Jan 4, 2020

Snowpack and Avalanche Discussion

<p>The combination of heavy snowfall earlier this week (1-2 ft with 1-1.7” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>), strong winds, and weak layers in the snowpack have created dangerous avalanche conditions. Avalanches can break beneath the new snow (1-2 ft deep), in a wind drift (3-4 ft deep), or on weak layers near the ground. Numerous natural and human triggered avalanches have been reported in the Bridger Range, near Big Sky, and near Cooke City (<a href="https://www.mtavalanche.com/weather/wx-avalanche-log">avalanche log</a>). Snowfall totals, the amount of wind drifting, and the distribution of weak layers varies a bit between the different mountain ranges, but from a practical perspective it makes no difference. Triggering a large avalanche is likely on any steep slope.</p>

<p>Yesterday, Alex went to the Throne in the northern Bridger Range and found just about every <a href="https://avalanche.org/avalanche-tutorial/red-flags/#avalanches">red flag</a> of avalanche danger. He saw a large natural avalanche on Saddle Peak while driving up the highway, had the snowpack collapse under him, got unstable test results, and had strong winds quickly drifting snow over his tracks (<strong><a href="https://www.youtube.com/watch?v=17YyGFhlMpU&amp;list=PLXu5151nmAvSbcbVf…;). He heeded these signs and stuck to slopes less than 30 degrees.</p>

<p>Last weekend, skiers in the Tobacco Root Mountains (outside our advisory area) <a href="https://avalanche.org/avalanche-encyclopedia/remote-trigger/">remotely triggered</a> an avalanche that broke 6 ft deep on the adjacent face while they were on a lower angled ridgeline (<a href="https://www.mtavalanche.com/images/20/remote-triggered-tobacco-root-mtn…;). They had dug three snowpits during their ascent of the ridgeline with no signs of instability. Their first indication of unstable snow was triggering this huge slide. There is no need for complicated snowpack assessments today. There has been lots of new snow (<strong><a href="https://www.youtube.com/watch?v=pStZS8rCbJ0&amp;list=PLXu5151nmAvSbcbVf…;). There are thick fresh wind drifts (<strong><a href="https://www.youtube.com/watch?v=17YyGFhlMpU&amp;list=PLXu5151nmAvSbcbVf…;). And on some slopes this is all stacked onto unstable weak layers (<strong><a href="https://www.youtube.com/watch?v=Ww-vCQEg-wA&amp;list=PLXu5151nmAvSbcbVf…;). Avoid steep slopes to avoid triggering a large avalanche. Human triggered avalanches are likely and the avalanche danger is CONSIDERABLE.</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>

Upcoming Avalanche Education and Events

Our education calendar is full of awareness lectures and field courses. Check it out and plan to attend one or two: Events and Education Calendar.

COOKE CITY

Every Friday and Saturday, Snowpack Update and Rescue Training. Friday, 6:30-7:30 p.m. at the Soda Butte Lodge. Saturday anytime between 10-2 @ Round Lake.

WEST YELLOWSTONE