18-19

GNFAC Avalanche Forecast for Mon Feb 18, 2019

Snowpack and Avalanche Discussion

<p>Over the weekend, light snowfall and minimal wind gave buried weak layers time to recover from the stress of last week’s 3-4’ of heavy snow (<u><strong><a href="https://www.mtavalanche.com/weather/wx-avalanche-log">weather log</a></strong></u>). In the mountains near West Yellowstone and the southern Madison and Gallatin ranges it is possible to trigger avalanches that break on weak, sugary snow at the base of the snowpack (<u><strong><a href="https://www.mtavalanche.com/images/19/big-snowmobile-triggered-avalanch…;). These deep avalanches are becoming difficult to trigger, but the consequences are deadly. On Saturday, Eric rode in Taylor Fork and saw a cornice triggered avalanche that broke at the base of the snowpack and deposited debris 10’ deep (<u><strong><a href="https://www.mtavalanche.com/images/19/large-natural-avalanche-taylor-fo…;, <u><strong><a href="https://www.youtube.com/watch?v=kIPUqVPE0g8&amp;list=PLXu5151nmAvRNl9ku…;). Yesterday skiers near Bacon Rind saw recent large natural avalanches, similar to what is possible to trigger today (<strong><a href="https://www.mtavalanche.com/node/20120">details</a></strong&gt;). Wind loaded slopes are particularly dangerous. Cornices have grown large and could fall and trigger a big avalanche (<u><strong><a href="https://www.mtavalanche.com/images/19/large-cornices-sunlight-basin">ph…;). Today, avoid steep wind loaded slopes and be extra cautious of all steep slopes. Large avalanches are possible to trigger and avalanche danger is <strong>MODERATE</strong>.</p>

<p>In the mountains near Bozeman, Big Sky and Cooke City weak layers in the lower half of the snowpack are not as widespread, but exist on some slopes. Yesterday two avalanches were triggered by snowmobilers on Buck Ridge near Big Sky (<strong><a href="https://www.mtavalanche.com/node/20123">details</a></strong&gt;, <strong><a href="https://www.mtavalanche.com/node/20131">details</a></strong&gt;), and one was triggered on Crown Butte near Cooke City (<strong><a href="https://www.mtavalanche.com/node/20128">details</a></strong&gt;). All three were on wind loaded slopes and broke 3-4’ deep, likely on persistent weak layers. On Friday near Cooke City I saw an avalanche that was 4-8’ deep and triggered by a cornice fall on a heavily wind loaded slope (<u><strong><a href="https://www.youtube.com/watch?v=oOjaEWyCVdI&amp;index=2&amp;list=PLXu51…;, <u><strong><a href="https://www.mtavalanche.com/node/20085">details</a></strong></u&gt;). Some slopes are strong while others are weak. This is why we carefully assess each slope, carry rescue gear and only expose one person at a time. In case we get surprised.</p>

<p>Doug and Ian rode the entire area north of Cooke City yesterday and noted only one avalanche which broke in the new snow (<strong><a href="https://www.mtavalanche.com/node/20115">details</a></strong&gt;, <strong><a href="https://www.youtube.com/watch?index=2&amp;list=PLXu5151nmAvRNl9kuY3DxfW…;). Over the weekend similar slides were reported in Hyalite (<strong><a href="https://www.mtavalanche.com/node/20125">details</a></strong&gt;), Beehive (<strong><a href="https://www.mtavalanche.com/images/19/natural-avalanches-beehive">photo…;), the Bridger Range (<u><strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-avalanches-throne…;, <u><a href="https://www.mtavalanche.com/images/19/skier-triggered-avalanches-throne…;) and Cooke City (<u><strong><a href="https://www.mtavalanche.com/images/19/natural-avalanche-near-cooke-city…;). Today these soft slabs of recent snow are possible to trigger on previously wind loaded slopes. Avoid steeper terrain if you see cracking in the snow surface, and dig 3-4’ to check for unstable weak layers. Avalanches of recently drifted snow are possible and can break deeper on specific slopes where buried weak layers exist. Avalanche danger is <strong>MODERATE</strong> on wind loaded slopes and <strong>LOW</strong> on non-wind loaded slopes.</p>

<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <u><a href="https://www.mtavalanche.com/node/add/snow_observation">website</a></u&gt;, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u&gt;), phone (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: Events and Education Calendar.

BOZEMAN

February 22 and 23, Women’s Companion Rescue Clinic, 6-8 p.m. Friday at REI, 10-4 Saturday in the field. More Info and Register.

Natural activity in Beehive

Beehive Basin
Northern Madison
Code
SS-N-R2-D1.5
Notes

On Saturday (2/16) skiers in Beehive observed "Lots of natural avalanches from Friday nights snow. Notice the large cornice sections at the base of the slope. We were impressed with the size of the cornices on the ridge. We noted no collapsing or cracking on the skin up or ski down."

Multiple Avalanches
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
R size
2
D size
1.5
Problem Type
Wind-Drifted Snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

On Saturday (2/16) skiers in Beehive observed "Lots of natural avalanches from Friday nights snow. Notice the large cornice sections at the base of the slope. We were impressed with the size of the cornices on the ridge. We noted no collapsing or cracking on the skin up or ski down." Photo: A. Crawford

Avalanche Details: Natural activity in Beehive
Northern Madison, 2019-02-18

Snowmobile-triggered avalanche on First Yellowmule

Buck Ridge
Southern Madison
Code
HS-AMu-R3-D2-O
Elevation
9300
Aspect
SE
Latitude
45.15950
Longitude
-111.33500
Notes

This avalanche failed on the ground up on Buck Ridge near the First Yellowmule. It was human-triggered, but nobody was caught or buried. Photo: N. James

Number of slides
1
Number caught
0
Number buried
0
Number killed
0
Avalanche Type
Hard slab avalanche
Trigger
Snowmobile
Trigger Modifier
u-An unintentional release
R size
3
D size
2
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
42.0 inches
Vertical Fall
50ft
Slab Width
100.00ft
Weak Layer Grain type
Faceted Crystals
Weak Layer grain size
2.50mm
Weak Layer Hardness
4F-
Slab Layer Grain Type
Wind packed
Slab Layer Hardness
1F+
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

Avalanche on Crown Butte

Crown Butte
Cooke City
Code
HS-R1-D2-G
Latitude
45.05200
Longitude
-109.95900
Notes

This avalanche on Crown Butte failed after multiple sleds had crossed the slope. From the email: "This one broke about 10 minutes after we’d been sledding below and across it. You can see our tracks going into it. Spooked us. The crown up top looked pretty deep, maybe 3 or 4 ft". Photo: S. Strenge

Number of slides
1
Number caught
0
Number buried
0
Number killed
0
Avalanche Type
Hard slab avalanche
R size
1
D size
2
Bed Surface
G - Ground
Problem Type
Wind-Drifted Snow
Slab Thickness
48.0 inches
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

This avalanche on Crown Butte failed after multiple sleds had crossed the slope. From the email: "This one broke about 10 minutes after we’d been sledding below and across it. You can see our tracks going into it. Spooked us. The crown up top looked pretty deep, maybe 3 or 4 ft". Photo: S. Strenge

Cooke City, 2019-02-18

This avalanche on Crown Butte failed after multiple sleds had crossed the slope. From the email: "This one broke about 10 minutes after we’d been sledding below and across it. You can see our tracks going into it. Spooked us. The crown up top looked pretty deep, maybe 3 or 4 ft". Photo: S. Strenge

Cooke City, 2019-02-18

Skier-triggered soft slabs in Hyalite

Hyalite - main fork
Northern Gallatin
Code
SS-AS-R1-D1-I
Elevation
9000
Aspect
NE
Latitude
45.48790
Longitude
-110.98100
Notes

Skiers reported triggering soft wind slabs in Hyalite on NE aspect at 9000'. Photo: T. Chingas

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Soft slab avalanche
Trigger
Skier
R size
1
D size
1
Bed Surface
I - Interface between new and old snow
Slab Thickness units
centimeters
Single / Multiple / Red Flag
Single Avalanche
Advisory Year