20-21

From email: "I toured into Blackmore [2/19/21] and observed an old snow avalanche at 9600' on the east face of Mt Blackmore. I was there the day before and didn't see any evidence of avalanche activity; strong overnight winds with ample snow available for transport appeared to be enough to tip the scales." Photo: T. Guarino

Northern Gallatin, 2021-02-19

From email: "I toured into Blackmore [2/19/21] and observed an old snow avalanche at 9600' on the east face of Mt Blackmore. I was there the day before and didn't see any evidence of avalanche activity; strong overnight winds with ample snow available for transport appeared to be enough to tip the scales." Photo: T. Guarino

Northern Gallatin, 2021-02-19

Natural avalanche below Maid of the Mist

Maid of the Mist
Northern Gallatin
Code
SS-N-R4-D2
Elevation
8400
Aspect
E
Latitude
45.41640
Longitude
-110.97000
Notes

An ice climber in Hyalite reported a natural D2 underneath the Maid today. Looked like it ran yesterday (2/18/21).

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
4
D size
2
Vertical Fall
500ft
Slab Width
200.00ft
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

From email: "While on tour today above the canyon, we observed various snow surfaces. We found heavily windloaded slopes on E/NE aspects. Solar aspects began to develop rollers as rocks began to heat up around noon. We observed a small avalanche on E slope a drainage away, roughly 20 feet wide. While ascending a ridgeline at 7500 elevation, we had a massive woomph and crack that spread 100 feet from the ridge to a roller in the fall line." Photo: Tommy S.

Northern Madison, 2021-02-19

GNFAC Avalanche Forecast for Fri Feb 19, 2021

Snowpack and Avalanche Discussion

<p>Strong winds yesterday drifted the abundant fresh snow and continued to load many slopes. Around noon yesterday, an avalanche broke naturally, several feet deep, on a heavily wind-loaded slope in the Bridger Range, south of Saddle Peak (<a href="https://www.mtavalanche.com/images/21/natural-avalanche-south-saddle-pe…;). With a bit more new snow and continued winds, similar slides will be easily triggered today, especially on wind-loaded slopes. Avalanches that initially break beneath the new and wind-drifted snow will likely step down to the lower weak layers, mid-pack or near the ground.&nbsp;</p>

<p>Continued snowfall may obscure subtler signs of wind-loading, but be especially skeptical of slopes beneath cornices and those with large drifted pillows directly below ridgelines. Avoid travelling on, or beneath, slopes steeper than 30 degrees. Conservative decision making is essential today. With natural avalanches possible and human triggered slides likely, the avalanche danger is rated CONSIDERABLE.</p>

<p>&nbsp;</p>

<p>With a similar weak snowpack structure in the southern ranges, the consequences of triggering a slide are the same as up north, but without as much new snow the likelihood is a bit less. A large snowmobile triggered slide in Cabin Creek is a good reminder of the sort of slide we’re worried about (<a href="https://www.mtavalanche.com/node/24253"><u>details</u></a&gt;). With large, deadly avalanches a real possibility, avoiding all avalanche terrain is a very reasonable strategy. If you are going to poke on to steeper slopes, dig a snowpit and do some snowpack tests before committing and then only expose one person at a time. The avalanche danger is MODERATE today.</p>

<p>Around Cooke City, the primary concern is avalanches breaking on wind-loaded slopes. A snowmobile triggered slide yesterday on Crown Butte highlights this concern (<a href="https://www.mtavalanche.com/images/21/snowmobile-triggered-slide-crown-…;, <a href="https://www.mtavalanche.com/images/21/snowmobile-triggered-slide-crown-…;). More snowfall and wind today will create fresh drifts on top of the older drifts and you could trigger either. Dave was in Cooke City the last few days and is cautiously optimistic about the strength of the lower snowpack, but didn’t rule out the possibility of triggering a deeper slide if you hit an atypically thin spot (<a href="https://www.youtube.com/watch?v=tzo-kbMbDUc"><strong><u>Wednesday video</u></strong></a>, <a href="https://www.youtube.com/watch?v=w4BEGFLhQWY"><strong><u>Thursday video</u></strong></a>). For today the avalanche danger is rated MODERATE.</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>

BEEHIVE BASIN AVALANCHE ACCIDENT REPORT

We posted a detailed report from Sunday's fatal avalanche in Beehive Basin here

The video of our accident investigation from the field is here.

 

Snowmobile Triggered Slide on Crown Butte

Crown Butte
Cooke City
Code
SS-AMu-R2-D2
Latitude
45.05250
Longitude
-109.96200
Notes

Snowmobile triggered slide on Crown Butte, 2/18/2021. 

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
2
D size
2
Slab Thickness
24.0 inches
Vertical Fall
500ft
Slab Width
300.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year