19-20

Natural Avalanches, Wilson Peak

Wilson Peak
Northern Madison
Code
HS-N-R2-D2.5-U
Elevation
10200
Aspect
S
Latitude
45.32700
Longitude
-111.32500
Notes

By far the most interesting thing today is an avalanche cycle on the south face of Wilson Peak. Multiple avalanches, some breaking on planar faces, scattered all across the thing. Not sure on depth either- some look quite deep, but I’m wondering if it is the storm snow from the mega-storm 2 weeks ago running on the rock hard surface leftover from the 100+ mph wind event 2.5 weeks ago. We will look more closely with binoculars tomorrow for a better estimate of scale. The slopes were obviously cross-loaded, but we were interested in what exactly made them cycle today (or last night).

Number of slides
3
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Natural trigger
R size
2
D size
2.5
Bed Surface
U - Unknown
Problem Type
Persistent Weak Layer
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

GNFAC Avalanche Forecast for Wed Feb 19, 2020

Snowpack and Avalanche Discussion

<p>New snow and strong winds last week increased the avalanche hazard. This weekend numerous natural and human triggered slides occurred across the Bridger, Madison, and Gallatin Ranges and in the mountains around Cooke City. Reports are still coming in. Yesterday, a human triggered avalanche north of Cooke City broke 3-4' deep and 100' across a small slope (<strong><a href="https://www.mtavalanche.com/node/22142">photo and details</a></strong>). Several natural avalanches on heavily wind loaded slopes on Wilson Peak likely failed Monday night. On Monday at Buck Ridge, a snowmobiler triggered a large avalanche more than four feet deep that failed on weak snow near the ground (<a href="https://www.mtavalanche.com/node/22129"><strong>details</strong></a&gt;). These recent events are clear evidence that human triggered avalanches are still possible. Go to our <a href="https://www.mtavalanche.com/avalanche-activity"><strong>avalanche activity page</strong></a> to learn more about this avalanche cycle.</p>

<p>As high pressure settles into the advisory area, it will be harder to trigger avalanches on deeply buried weak layers. Persistent weak layers, such as the widely distributed weak, sugary snow near the ground, are tricky. Signs of instability like natural avalanches and collapsing will not be forthcoming today and you may get stable test results but keep the big picture in mind. This weekend the mountains reached a tipping point and large, destructive avalanches occurred on this layer and within the new snow. Doug wouldn’t trust the snowpack at Mount Ellis on Monday (<a href="https://www.youtube.com/watch?v=3zzAAW7wFzk"><strong>video</strong></a&…;) and, in Cooke City, this deeply buried weak layer kept us making relatively conservative decisions even though the mountains and stability tests presented us with no signs of volatility (<a href="https://youtu.be/kzAyDyTQsgs"><strong>video</strong></a&gt;).</p>

<p>Today, make conservative terrain choices to avoid the hazard or carefully assess stability and manage your exposure if you are going into avalanche terrain. The avalanche danger is rated MODERATE.</p>

<p>In the mountains around West Yellowstone, stability has improved. There has been no avalanche activity reported in the area in the last ten days. Riders are out and climbing hills and not triggering slides. We rode up Denny Creek and Lionhead Ridge two times in the last week and a half and were pleasantly surprised both times by the lack of avalanche activity, the absence of signs of instability following a significant loading event and that weak snow near the ground is gaining strength (<a href="https://www.youtube.com/watch?v=S_gUqe5axGQ&amp;feature=youtu.be"><stro… Hill video</strong></a><strong>, </strong><a href="https://www.youtube.com/watch?v=vOKh3V6ZDJ0&amp;list=PLXu5151nmAvSbcbVf… Creek video</strong></a>). The avalanche danger is LOW and human triggered avalanches are unlikely. Continue to follow standard avalanche safety protocols by carrying all avalanche rescue gear, assessing steep slopes for isolated instabilities, and exposing only one person at a time to potential hazards.</p>

<p>If you get out, please send us your observations no matter how brief. You can fill out an&nbsp;<a href="https://mtavalanche.us17.list-manage.com/track/click?u=6653a830e4819c9e…; target="_blank"><strong>observation form</strong></a>, email us (<a href="mailto:mtavalanche@gmail.com&quot; target="_blank"><strong>mtavalanche@gmail.com</strong></a>), 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

Snowmobiler triggered small avalanche near Goose Lake

COOKE CITY
Cooke City
Code
SS-AMu-R1-D1.5
Aspect
S
Latitude
45.02020
Longitude
-109.93800
Notes

"A small slide approx 100 ft wide ran about 40 vertical feet. Crown was 3-4 feet deep. Aspect, SE. Trigger unknown however tracks indicate it was likely a snowmobile trigger."

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
1
D size
1.5
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

"A small slide approx 100 ft wide ran about 40 vertical feet. Crown was 3-4 feet deep. Aspect, SE. Trigger unknown however tracks indicate it was likely a snowmobile trigger." Photo: Reed Youngbar

Cooke City, 2020-02-19

Collapsing/Whumphing at Bear Canyon

Mt Ellis
Northern Gallatin
Code
Elevation
6800
Latitude
45.57770
Longitude
-110.95500
Notes

A group reported: "On Sunday afternoon my partner and I skinned up Bear Canyon and proceeded a half mile south along the ridge from the top of the ski hill. We were considering skiing a treed gully off the ridge down into Shoefelt gulch or skiing the East side of the ridge back into New World Gulch. As we skinned out of the trees (@ 6,800 ft) and out into the meadow above our prospective runs I caused a very audile collapse and it was obvious the wind had done a lot of work moving snow on to the east facing slope. We dug a snow pit, on a west facing slope, about 30 feet down from the ridge. The snowpack in our pit was 95CM deep, we did an extended column test and got an ECTP 13 which failed on the facets near the ground. The slab was ~70 CM. We decided to dig another pit on the east facing slope just across the ridge, making sure not to get too close to gully which looks like a slide path. My partner dug out the majority of the pit and then I joined him to perform another ECT. Just before we isolated our column my partner stepped out of the pit for a second and on he triggered another extremely audible collapse that seemed to have traveled a decent ways across the slope to the north of us, towards the gully. We got an ECTP 12 from this pit, it broke on the facets near the ground and the slab was about 80CM, the snow depth was 100CM. I thought it was interesting that we did not see much cracking while we were skinning or digging our pits, that being said the new snow from this last storm cycle was very dense and it was easy to get it to sheer when we were digging pits but we did not see it collapse. We knew going up that we probably couldn't ski any of what we checked out but had good time looking at the snowpack and skiing with the dogs back down the ridge to Bear Canyon."

Number of slides
0
Number caught
0
Number buried
0
Problem Type
Persistent Weak Layer
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Red Flag
Advisory Year

Natural Avalanche up Moose Jaw, Storm Castle Ridge

Moose Jaw
Northern Gallatin
Code
HS-N-R3-D3-O
Elevation
9200
Aspect
N
Latitude
45.44940
Longitude
-111.07600
Notes

Very large avalanche photographed from Gallatin Gateway at the head of Little Bear Canyon. This avalanche likely occurred Saturday or Sunday during the loading event as there is snow on the debris pile. 

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Natural trigger
R size
3
D size
3
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
60.0 inches
Vertical Fall
500ft
Slab Width
1100.00ft
Weak Layer Grain type
Faceted Crystals
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year