18-19

Today the YC Ski Patrol conducted avalanche mitigation work above one of our roads. The area is outside of our ski area boundary and receives no skier traffic. A 2lb explosives charge was detonated from an aerial tram and triggered a R4/D3 avalanche that ran to the ground on depth hoar. The crown was 4', The max path width was around 250', and it ran 350 vertical feet to the bottom of the runout zone. The elevation was 8400' on a ENE aspect and max slope angle of 36 degrees.

Northern Madison, 2019-03-03

Large Natural Avalanche, Wilson Peak northern Madison Range

Wilson Peak
Northern Madison
Code
HS-N-R4-D3.5-O
Elevation
9700
Aspect
SW
Latitude
45.32490
Longitude
-111.33300
Notes

Big Sky ski patrol reported this slide on Friday (3/1). It broke sometime Thursday night or early Friday.

Number of slides
1
Number caught
0
Number buried
0
Avalanche Type
Hard slab avalanche
Trigger
Natural trigger
R size
4
D size
3.5
Bed Surface
O - Old snow
Problem Type
Persistent Weak Layer
Slab Thickness
48.0 inches
Vertical Fall
1200ft
Slab Width
1000.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Single Avalanche
Advisory Year

GNFAC Avalanche Forecast for Sat Mar 2, 2019

Snowpack and Avalanche Discussion

<p>A break in the weather yesterday allowed the avalanche warning to expire and gave the snowpack a well needed sigh of relief. After being inundated by multiple feet of snow over the past week, the snowpack is slowly adjusting and stability is gradually improving.</p>

<p>Yesterday, Alex and I rode into Taylor Fork in the southern Madison Range and we were pleasantly surprised by the lack of recent avalanche activity. However, the snowpack remains under a significant amount stress and human triggered avalanches remain likely.</p>

<p>Slides breaking 1-3’ deep in new and wind-blown snow is the main concern. Yesterday, a skier outside of Cooke City observed numerous natural avalanches that failed in the new snow. Today, similar slides are likely, mainly on slopes with wind drifted snow (<strong><a href="https://www.mtavalanche.com/images/19/natural-slab-avalanche-near-cooke…;, <strong><a href="https://www.mtavalanche.com/images/19/natural-avalanche-cooke-city-0">p…;). A less probable but more dangerous problem are slides breaking on weak layers buried deep in the pack (<u><strong><a href="https://www.youtube.com/watch?v=vXUCG2z6fYI&amp;list=PLXu5151nmAvRNl9ku…;). Slides failing in the new snow could step down and trigger on of these monsters, or a skier or rider could find a specific trigger point that could release the entire slope.</p>

<p>Today, careful snowpack evaluation and conservative decision making are essential. Dangerous avalanche conditions exist and the avalanche danger is rated <strong>CONSIDERABLE</strong>.</p>

<p>Wind loaded slopes are the main concern in the mountains around Bozeman and Big Sky. Wind drifts will be largest and most widespread on upper elevation slopes loaded by west-southwest winds. Be especially aware of this problem on steep slopes below ridgelines, on the sides of cross loaded gullies, and below exposed cliff bands (<u><strong><a href="https://www.mtavalanche.com/images/19/skier-triggered-slide-north-big-s…;). Consider the consequences of triggering a slide before committing to avalanche terrain. Even small slides can be deadly if they carry you over rocks or push you into trees. The avalanche fatality in the Bridger Range on Tuesday&nbsp;is a reminder of how specific terrain can increase the consequences of being caught in a slide. Read the full accident report <strong><a href="https://www.mtavalanche.com/sites/default/files/accident-reports/2019-0…;. &nbsp;</p>

<p>Although most slides will stay confined to the upper 1-2’ of the snowpack, deep slab avalanches remain a possibility. A large slide on Wilson Peak near Big Ski is a reminder that persistent weak layers near the ground still exist and can fail under the right conditions (<strong><a href="https://www.mtavalanche.com/images/19/large-natural-avalanche-wilson-pe…;). These types of slides are becoming less likely, but can’t be entirely ruled out.</p>

<p>Today, human triggered avalanches are likely on wind loaded slopes which have a <strong>CONSIDERABLE</strong> avalanche danger. Non-wind loaded slopes have a <strong>MODERATE</strong> avalanche danger.</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

Today and tomorrow, Bozeman Split Fest, More info at www.bozemansplitfest.com.

March 6, 1-hr Avalanche Awareness, 6-7 p.m. at REI Bozeman.

COOKE CITY

Multiple Naturals, Cooke City

COOKE CITY
Cooke City
Code
SS-N-I
Latitude
44.97440
Longitude
-110.08700
Notes

A skier in Cooke City noticed multiple avalanches around Mt. Horinday, Barronette Peak and Mt. Republic. Most avalanches appear to have failed within the new snow or at the interface between new and old snow. However, one of the slides on a steep, rocky convexity on Mt. Republic failed 3-4' deep on a persistent weak layer.

Multiple Avalanches
Number caught
0
Number buried
0
Number killed
0
Avalanche Type
Soft slab avalanche
Trigger
Natural trigger
Bed Surface
I - Interface between new and old snow
Slab Thickness
18.0 inches
Slab Width
50.00ft
Slab Thickness units
inches
Single / Multiple / Red Flag
Multiple Avalanches
Advisory Year

From the email: "Had a good look around from the Lamar Valley up to Cooke first thing this am, and the epicenter of the avalanche activity appeared to be around Mt. Horinday and Barronette Peak.  Lots of slab avalanches on the east face of Barronette.  Most looked to be about 1-2' deep.  Much quieter the further up valley toward Cooke City you went." Photo: B. Fredlund

Cooke City, 2019-03-01