17-18

GNFAC Avalanche Advisory for Sun Mar 25, 2018

Snowpack and Avalanche Discussion

<p>The storm yesterday favored the mountains near Bozeman and Big sky with 8-11” of snow equal to 0.7 - 1.2” of snow water equivalent (SWE). Strong south-southwest wind drifted the new snow into wind slabs that are easy to trigger today. These wind slabs are located near ridgelines as well as across mid-slope rollovers and along the bottom of cliffs.</p>

<p>Yesterday, skiers triggered avalanches in Beehive Basin and reported snow easily sliding on buried crusts (<strong><a href="https://www.mtavalanche.com/images/18/skier-triggered-slides-beehive-ba…;, <strong><a href="https://www.mtavalanche.com/images/18/skier-triggered-slides-beehive-ba…;). I was skiing&nbsp;nearby and found the potential for similar, unstable conditions (<strong><a href="https://youtu.be/GgZtfI4E2DQ">video</a></strong&gt;). Eric was in Tepee Basin and found 8-10” of new snow and strong wind created unstable conditions on wind loaded slopes (<strong><a href="https://youtu.be/iaHHEql8ZwU">video</a></strong&gt;). Skiers in the northern Bridger Range saw a recent natural avalanche and fresh wind slabs forming in the afternoon. Today, wind loaded slopes deserve extra caution and should be avoided.</p>

<p>On non-wind loaded slopes, wet or dry loose avalanches are possible and can run long distances on firm crusts underneath. Below recent snow the snowpack is generally stable and deeper avalanches are not likely. Doug was in Bacon Rind yesterday and found a stable snowpack, but warned of quick changes that take place during long and sunny spring days (<strong><a href="https://youtu.be/akf_B1M9TQk">video</a></strong&gt;). Brief glimpses of sunshine today can make wet loose avalanches easy to trigger or release naturally (<a href="https://www.youtube.com/watch?v=W_mcy_fnF44"><strong>video</strong></a&…;). Thorough and continuous snowpack and terrain assessment is essential.</p>

<p>New snow and strong wind yesterday make avalanches easy to trigger on wind loaded slopes, and possible on all steep slopes. Avalanche danger is CONSIDERABLE on wind loaded slopes and MODERATE otherwise.</p>

<p>The mountains near West Yellowstone and Cooke City got 2-5” of new snow equal to .2-.4” of SWE. This new snow was drifted into fresh wind slabs by strong south-southwest wind yesterday. Today, wind slabs are possible to trigger and wind loaded slopes deserve caution. Skiers near Cooke City have noted recent natural wind slabs over the last week (<strong><a href="https://www.mtavalanche.com/images/18/natural-wind-slabs-0">photo</a></…;, <strong><a href="https://www.mtavalanche.com/images/18/natural-wind-slabs-cooke">photo</…;), and they have reported the new snow easily sliding on recently buried, firm crusts. Dry or wet loose avalanches of recent snow are possible to trigger on steep slopes and can run long distances with a lot of volume. Recent snow and wind make avalanches possible today, and avalanche danger is rated MODERATE.</p>

<p>If you get out and have any avalanche or snowpack observations to share, drop a line via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a&gt;, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a&gt;), phone (406-587-6984), or Instagram (#gnfacobs).</p>

Skiers in Beehive Basin noted touchy conditions and poor bonding between the new snowfall and old snow interface. Crusts formed last week during several days of high pressure, particularly on solar aspects. They also noted natural avalanche activity. Photo: R. Makohin

Northern Madison, 2018-03-24

There is 7' of snow on the ground in Bacon Rind (HS 240 cm) and it is stable today. The main concern is the new snow above the ice crust that formed 10 days ago (seen as the stripe behind the shovel) and in two snowpits our stability tests did not propagate. Melting, rain and/or more snow with wind would change the stability, but for now it's good. Photo: GNFAC

Southern Madison, 2018-03-24