19-20

An avalanche was triggered on 2/27/2020 at 8:30 p.m. by a groomer between Storm Castle and Swan Creeks in the northern Gallatin Range. The driver was ok, but the machine did a full barrel roll and was very badly damaged. Photo: GNFAC

Northern Gallatin, 2020-02-28

Skier triggered small slab and natural loose on Black Mtn. Absaroka

Black Mountain
Out of Advisory Area
Code
SS-AS-R1-D1-S
Elevation
9000
Aspect
S
Aspect Range
N, S
Latitude
45.16280
Longitude
-111.52900
Notes

While approaching Black Mountain from Pine Creek Lake. Noticed two dry loose snow problems on the way up near rock bands on North facing aspects at 9500'. R1.5 D1. Winds were powerful around 30mph at the summit and on the approach our major concern was wind slab problem reacting around 5 inches deep. We skied South aspect and as it warmed we triggered D1 R1 slabs that ran slow and short. Although we never skied on substantial slabs, we were eager to get moving and out of any run outs.

Number of slides
2
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
R size
1
D size
1
Bed Surface
S - Avalanche released within new snow
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

Natural small wind slab and dry loose near Cooke

COOKE CITY
Cooke City
Code
SS-N-R1-D1.5-S
Elevation
9300
Aspect
NE
Latitude
45.02020
Longitude
-109.93800
Notes

From email 2/28: "Photo attached of a natural avalanche from yesterday, just south of Cooke City.  It's on an E, NE aspect, with a crown around 9,300'.  Looks like it occurred yesterday am, as a result of a cornice fall.  

Additionally we observed quite a few natural, point release avalanches on mid elevation easterly aspects yesterday too.  Lots of sunshine, and temperatures in the valley bottom slightly above freezing yesterday.

Overall we didn't find the fresh wind drifts to be too widespread though."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
1
D size
1.5
Bed Surface
S - Avalanche released within new snow
Problem Type
Wind-Drifted Snow
Slab Thickness
8.0 inches
Vertical Fall
700ft
Slab Width
20.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

GNFAC Avalanche Forecast for Fri Feb 28, 2020

Snowpack and Avalanche Discussion

<p>Strong and gusty west winds continue to drift snow (<strong><a href="https://www.youtube.com/watch?v=WPLN1ArW5vo">video</a>)</strong&gt;. Avalanches can break in these drifts or if you get unlucky on weak snow near the ground. With a substantial load of new snow earlier this week, continued wind loading, and a history of big avalanches breaking at the ground we don’t have a lot of confidence in the snowpack (use the <strong><a href="https://www.mtavalanche.com/weather/wx-avalanche-log">Weather and Avalanche Log</a></strong> to refresh your memory). Be particularly wary of freshly wind drifted slopes. Watch for shooting cracks as a sign the newly drifted snow is unstable.</p>

<p>Yesterday, an avalanche broke 4 ft deep and 300 ft wide up Storm Castle creek and pushed the groomer off the trail (<strong><a href="https://www.mtavalanche.com/node/22269">details</a></strong&gt;). Luckily the operator was okay, but without the protection of his machine things could have turned out differently. On Wednesday, a cornice broke at the top of the Hourglass Chute north of Bridger Bowl and triggered a 3-4 foot deep x 100-foot wide slide on weak snow at the ground (<strong><a href="https://www.mtavalanche.com/node/22257">photos and details</a></strong>). These slides are a clear demonstration that triggering avalanches on these weak layers is still possible. With a deeply buried weak layer capped by a hard slab it will take finding just the wrong spot to trigger a slide. Don’t pay attention to other tracks on a slope, it could easily be the 10<sup>th</sup> rider that triggers the monster avalanche.</p>

<p>The avalanche danger is rated MODERATE today.</p>

<p>The snowpack near Cooke City and West Yellowstone is generally stable. You could trigger small wind drifts, but these will not be much of an issue unless you’re in high consequence terrain. It has been several weeks since the last reported avalanche on the weak layers at the ground (<strong><a href="https://youtu.be/9g-x7o56ek8">video</a></strong&gt;, <strong><a href="https://youtu.be/2IzNvRo0R3w">video</a></strong&gt;). However, yesterday skiers up Specimen Creek got a big collapse with the snowpack shifting an inch and a half downhill on a 30 degree slope (<strong><a href="https://www.mtavalanche.com/node/22267">details</a></strong&gt;). If the slope was just a few degrees steeper, it would have been an avalanche. Keep weak snow at the ground in the back of your mind and always be ready for the unlikely event that you do trigger a slide. The avalanche danger is rated LOW today.</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://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank">observation form</a></strong>, email us (<strong><a href="mailto:mtavalanche@gmail.com&quot; target="_blank">mtavalanche@gmail.com</a></strong>), 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.

BOZEMAN