Small slab avalanche and wind-loading on the north face of Mt Blackmore. Photo: B. Richards
Winds actively drifting the new snow into unstable slabs. Photo: GNFAC
Up the Dribbles today and tried to traverse over to Responsible but turned around after finding a 20cm wind slab in the gully that sheared easily in hand pits. Manageable terrain with the rope but we were concerned there were people below us. Winds increasing throughout the day, impressive plumes of snow coming off Hyalite, Divide, etc.
Group of 7 riding sheep creek basin.
We triggered 1 avalanche and seen 2 more in same area. All were on previous shoot areas. All broke about 1+ down.
No one buried or injured.
On a W facing slope in dense to gladed trees just east of the Republic Creek skin track, 8200" - 9200". Snow was not wind loaded at all. There was a buried weak layer about a foot below the new snow, but the new snow had not formed a slab so stability seemed good. There was one incident of a collapse crossing a small gully at about 40deg, a crack formed but did not slide probably due to no wind loading.
We skied Ghost Trees a handful of times on the 17th. I dug a pit and just updated it on SnowPilot this morning. The only instability we found was a small (2 meters wide) pocket that broke about 15 cm down as a result of a ski cut. It was on the far skiers right shoulder of the run at a convexity.
The following day on 18th we toured out into Hayden creek basin and skied some NE facing slopes across from Ollies woods. A lot of wind loading, the depth in my test pit was over 3 meters. I had a ECTX and we skied the slope. We did not observe any avalanche activity out there.
We triggered shooting cracks on a small, south-facing slope near Astral Lake, north of Cooke City. The cracks went down to a layer of surface hoar and facets on a crust. Photo: GNFAC
<p>The mountains around Cooke City received 7" of new snow with 0.6" of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a> (SWE) in the last 48 hours. Winds died down this morning but not before creating unstable drifts sitting on a layer of weak surface hoar buried a foot underneath the snow on many slopes. We found this layer reactive in our snowpits during the last two days of riding north of Cooke City, saw shooting cracks, and triggered a small avalanche on a test slope (<a href="https://www.youtube.com/watch?v=-AhOAQTfkHE&list=PLXu5151nmAvQDzKmH…;). A layer of sugary facets buried 2-3' deep on some slopes has also caused avalanches this season (<a href="https://mtavalanche.com/avalanche-activity"><strong>avalanche activity list</strong></a>). The challenge in Cooke City this year relates to spatial variability, meaning that the snowpack structure changes from relatively stable on one slope to relatively unstable on another (<a href="https://www.youtube.com/watch?v=J9oQHYge_gM"><strong>video</strong></a&…;). This was most clearly demonstrated in the case of the nearly fatal avalanche on the Fin ten days ago (<a href="https://mtavalanche.com/node/23644"><strong>avalanche details</strong></a>). The safest strategy is to maintain a healthy level of skepticism regarding slope stability and diligently manage your terrain.</p>
<p>Human-triggered avalanches are likely on wind-loaded slopes where the danger is rated CONSIDERABLE and possible on all other slopes where the danger is rated MODERATE.</p>
<p>The Bridger, Northern Gallatin, and Northern Madison Ranges received 4-7" of new snow in the last 48 hours equal to 0.3-0.7" SWE. The Southern Madison, Southern Gallatin, and Lionhead Ranges received less snow (2-3") but the story is the same. New snow fell onto a snowpack with two distinct weak layers. The first consists of a nearly universal layer of weak, sugary facets near the ground. Avalanches failing on this layer are becoming harder to trigger as the snowpack gets deeper while simultaneously becoming larger and more dangerous. The second is a layer of feathery surface hoar now buried under a foot of snow. This layer is not on all slopes but as Doug explained on Mount Blackmore yesterday, it is best to make terrain decisions assuming that it is present (<a href="https://www.youtube.com/watch?v=YzVvIsb7on4"><strong>video</strong></a>…;
<p>The wind will ramp up this afternoon into tomorrow, transporting the fresh snow into drifts that will crack and avalanche under a skier or rider's weight. Watch for signs that wind-loading is increasing, such as plumes of snow blowing off ridgelines or across slopes.</p>
<p>Large, human-triggered avalanches are possible today and the danger is rated MODERATE. With multiple persistent weak layers in the mix, ski and ride conservatively by staying off and out from under steep slopes.</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>website<…;, email (<a href="mailto:mtavalanche@gmail.com"><strong>mtavalanche@gmail.com</strong></a…;), phone (406-587-6984), or Instagram (#gnfacobs).</p>
See our education calendar for an up-to-date list of all local classes. Here are a few select upcoming events and opportunities to check out:
