19-20

Yesterday, the Big Sky Ski Patrol used explosives to trigger a very large deep slab avalanche on the North Summit Snowfield (<a href="https://www.mtavalanche.com/node/21746">details and photos</a>). It broke up to 10 feet deep, on weak snow near the ground. While it has been close to a week since a similar slide was triggered in the backcountry, this demonstrates that it remains possible if you find just the wrong spot. There are widespread weak layers near the ground capped by hard slabs of wind drifted snow. Warm temperatures will help heal the weak snow at the ground, but this is a painfully slow process. While we’re waiting, we need to keep traveling very conservatively (<a href="https://www.youtube.com/watch?v=4rzvTkbQDt4&list=PLXu5151nmAvSbcbVf…;). These large slides will be triggered from thinner areas, whether that’s near rocks or low on the slope where the wind slab thins (<a href="https://www.youtube.com/watch?v=MsjmwmAH7Ww&list=PLXu5151nmAvSbcbVf…;

Travelling in avalanche terrain today is like a game of Russian roulette. A couple chambers of the gun have been emptied since last weekend (reflecting the lowering likelihood of triggering a slide), but the potential consequences of pulling the trigger remain huge (<a href="https://www.youtube.com/watch?v=VXVEIqSWvdY&list=PLXu5151nmAvSbcbVf…;, <a href="https://www.youtube.com/watch?v=XQQ8I9DJd98&list=PLXu5151nmAvSbcbVf…;, <a href="https://www.youtube.com/watch?v=7vDe6LE-nhU&list=PLXu5151nmAvSbcbVf…;). Avoiding steep slopes is the safest plan today.

Alex was at Mt. Ellis yesterday in a snowpack at the opposite end of the spectrum. Instead of a deep hard slab problem he found a very weak, shallow snowpack (<a href="https://www.youtube.com/watch?v=-iokOWUdQ3s&list=PLXu5151nmAvSbcbVf…;). In these areas, we’re worried about places where wind loading or heavier snowfall has built a more cohesive slab on top of the facets.

Today, large avalanches are possible and the avalanche danger is rated MODERATE.

If you get out, please send us your observations no matter how brief. You can fill out an <a href="https://www.mtavalanche.com/node/add/snow_observation">observation form</a>, email us (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a>), leave a VM at 406-587-6984, or Instagram (#gnfacobs).

Read more about GNFAC Avalanche Forecast for Sat Jan 25, 2020

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

Explosive triggered Deep Slab Avalanche at Big Sky

Big Sky Resort

Northern Madison

1/24/2020

Code

HS-ABc-R4-D4

Latitude

45.27600

Longitude

-111.43600

Notes

A deep slab avalanche was triggered using explosives on 1/24/2020 in the North Summit Snowfield at Big Sky Resort.

From email: "The Whale came out close to 10’ deep that tapered to 3’ on the skiers right edge... It broke on basal facets, thin layer, 1F hard at crown (!) with very hard snow above and below the layer that failed .... It is likely that the layer that failed had some different characteristics lower in the path that avalanched away- possibly less hard."

Number of slides

Number caught

Number buried

Avalanche Type

Hard slab avalanche

Trigger

An explosive detonated above the snow surface (air blast)

Trigger Modifier

c-A controlled or intentional release by the indicated trigger

R size

D size