21-22

5 ft deep explosive triggered slide at Big Sky Resort

Big Sky Resort
Northern Madison
Code
HS-AE-R4-D3.5-O
Latitude
45.27600
Longitude
-111.43600
Notes

Big Sky Ski Patrol used explosives to trigger an avalanche that broke 5 ft deep on weak layers near the ground.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
An explosive thrown or placed on or under the snow surface by hand
R size
4
D size
3.5
Bed Surface
O - Old snow
Slab Thickness
60.0 inches
Slab Width
260.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

GNFAC Avalanche Forecast for Fri Dec 24, 2021

Snowpack and Avalanche Discussion

<p>A big dump of new snow with strong winds means that human triggered avalanches are likely today. The Fisher Creek SNOTEL site is showing 18” (1.8” <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/null/?cid=nrcseprd1314… Water Equivalent</u></a>) of snow over the last 48 hours and we’ve received reports of substantially more snow at higher elevations. You could trigger an avalanche within the new snow (especially in wind drifts), on a layer of weak snow in the middle of the snowpack, or on weak snow at the ground. Don’t get caught up in the details - with so much new snow, wherever a slide breaks it will be large and dangerous. Keep it simple. Stay off of and out from under any slope steeper than 30 degrees. Human triggered avalanches are likely and the avalanche danger is rated CONSIDERABLE.&nbsp;</p>

<p>With a foot of fresh snow (1.1” SWE) and strong southwest winds avalanches will break easily today on wind loaded slopes. Expect to trigger avalanches within the new snow and they could also break on the weak layers near the ground (<a href="https://youtu.be/7EEn6f8-4fA"><strong><u>video</u></strong></a&gt;). Look out for and avoid steep wind-loaded slopes. If you aren’t confident in identifying wind-loaded slopes, just avoid all steep slopes. The avalanche danger is CONSIDERABLE on wind-loaded slopes. On slopes without wind-drifted snow avalanches are possible and the avalanche danger is MODERATE.</p>

<p>Seven inches of new snow (0.7” SWE) isn’t enough to spike the danger, but does mean it’s possible to trigger dangerous avalanches on steep slopes that are either wind drifted or have weak snow at the base of the snowpack (<a href="https://youtu.be/2rjpm0iLm_I"><strong><u>Tepee Basin video</u></strong></a>). Look out for particularly deep wind-drifts or slopes where a small slide could pile up deeper in a gully or push you into obstacles. Human triggered avalanches are possible and the avalanche danger is MODERATE.</p>

<p>Fresh wind drifts are the primary concern near Bozeman and Big Sky. Yesterday, Alex and Doug triggered a small wind slab while looking at the snowpack on Saddle Peak (<a href="https://www.youtube.com/watch?v=_MhpDHnH8So"><strong><u>video</u></stro…;). With new snow and strong to extreme winds overnight, expect to find fresh reactive wind drifts on many slopes. While the lower snowpack is generally stable (<a href="https://youtu.be/cf-qqv2Ssjw"><strong><u>Buck Ridge video</u></strong></a>, <a href="https://youtu.be/ePMCJs3qAs0"><strong><u>Beehive video</u></strong></a>), yesterday, Big Sky Ski Patrol used explosives to trigger a 5 ft deep avalanche that broke on weak snow near the ground. Let this be a wake up call and reminder to not discount the basal weak layers that exist across our advisory area. The avalanche danger is rated MODERATE on wind-loaded slopes and LOW on all others.</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>

<p>&nbsp;</p>

Upcoming Education Opportunities:

Get your avalanche brain ready for the season at one of the many classes listed on our education calendar, and list of upcoming events below. 

Every Saturday near Cooke City, 10 a.m.-3 p.m. FREE snowpack update and transceiver/rescue training. Stop by for 20 minutes or more at the Round Lake Warming Hut.

Skier triggered small wind slab on Saddle Peak

Saddle Peak
Bridger Range
Code
HS-ASc-R1-D1-I
Elevation
9000
Aspect
E
Latitude
45.79430
Longitude
-110.93600
Notes

We were able to intentionally trigger this 6-8" deep wind slab on Saddle Peak on December 23, 2021, E aspect at 9,000'. It showed us that recently formed wind slabs were still reactive. This hard slab formed over low density new snow which made it unstable. While not large, these slides will easily push you down and can be harmful if they push you into hazardous obstacles or terrain traps. - GNFAC

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Skier
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Problem Type
Wind-Drifted Snow
Slab Thickness
7.0 inches
Vertical Fall
70ft
Slab Width
10.00ft
Weak Layer Grain type
Precipitation Particles
Weak Layer Hardness
F
Slab Layer Grain Type
Wind packed
Slab Layer Hardness
P-
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

We intentionally triggered this 6-8" deep wind slab on Saddle Peak on December 23, 2021, E aspect at 9,000'. It showed us that recently formed wind slabs were still reactive. This hard slab formed over low density new snow which made it unstable. While not large, these slides will easily push you down and can be harmful if they push you into hazardous obstacles or terrain traps. Photo: GNFAC

Bridger Range, 2021-12-23

Powell Mine North Flint Range

Date
Activity
Skiing

This is second hand from a reliable source in the Philipsburg ski/snowmobile community. Backcountry skiers on a north aspect near the Powell mine, North Flint Range, were digging a snow pit when the slope avalanched with the crown through their snow pit. Slab avalanche was estimated at 16 inches and slope was wind loaded. Avalanche ran 6-800 feet. Skiers stayed in the snow pit and no one was caught.

Region
Butte Area
Observer Name
Will Shoutis

Bacon Rind meadows

Date
Activity
Skiing

Obs are from Wednesday 12-22: Toured in afternoon from normal parking to ridge above low angle runs. OVC sky, Prec. S-1, cool temps -6 at TH, -10 at ridge. HS 35-40 at bottom, 70-80cm @8,260 ft, 110-120cm at ridge where wind protected on shady asps. HS is quite variable this season between the meltdown in early Dec. and abundant wind redistribution. Found as little as 40cm in wind affected areas even at 8800'. Test profile below ridge top in a protected zone, asp 70 deg, 25 deg slope, HS 115. Poor snowpack structure, 1F slab over a decomposed crust at 40cm, with layer of concern of 20cm of 4F- 2mm FC below. CTH21(Q1)x2 at 38cm. Layer will propagate a fracture, ECTP22@38 ish. No real news there, this is much the same as the obs from Buck and Tepee. No Whumpfing observed, and I did break substantial different trail in the meadows. Isolated Cracking around skiis in shallow areas. Travel conditions are good up high, marginal at low elevs.

Region
Southern Madison
Location (from list)
Bacon Rind
Observer Name
Mike Best