GNFAC Avalanche Forecast for Thu Jan 10, 2019
<p>The mountains south of Big Sky to West Yellowstone have a weak and unstable snowpack. It is weak because sugary facets making up the lower half of the snowpack are unsupportable (<u><strong><a href="https://www.mtavalanche.com/images/19/poor-structure-s-madison-range">p…; <u><strong><a href="https://www.youtube.com/watch?v=l0aklSLqYaM&list=PLXu5151nmAvRNl9ku…;). A person will sink to the ground when they step off their snowmobile or skis. The snowpack is unstable because there is enough weight from new and windblown snow to create natural avalanches, cracking and collapsing. Yesterday morning a large natural avalanche released on the heavily wind-drifted Lionhead Ridge (<strong><a href="https://www.mtavalanche.com/node/19639">details</a></strong>), and skiers in Taylor Fork got a large collapse with shooting cracks on a wind-loaded slope (<strong><a href="https://www.mtavalanche.com/images/19/cracking-and-collapsing-taylor-fo…;, <strong><a href="https://www.mtavalanche.com/node/19638">details</a></strong>). This is the fourth day in a row of <strong><a href="https://www.mtavalanche.com/avalanche-activity">avalanche activity</a></strong>. Today, wind-loaded slopes have a CONSIDERABLE avalanche danger and should be avoided. All other slopes have a MODERATE danger.</p>
<p>Whenever we go in the field we always have a question that needs to be answered. Yesterday I wanted to know if the shallowest and weakest snow in the northern areas is getting stronger, so my partners and I toured on Mt. Ellis. The snowpack was only 2-3 feet deep with the bottom two-third consisting of unsupportable facets. We did not get any collapsing or cracking on open slopes and our 2 snowpits showed improving stability (<strong><a href="https://www.youtube.com/watch?v=cljvf0-9vyU&list=PLXu5151nmAvRNl9ku…;). In the absence of new snow or wind-loading the snowpack is getting stronger.</p>
<p>The avalanche near Ross Peak in the Bridger Range on Saturday is still relevant as an example of our current avalanche concern (<u><strong><a href="https://www.mtavalanche.com/node/19583">details</a></strong></u><u>)</u>. A hard slab of windblown snow sitting on a foot or more of weak facets could be triggered. The northern ranges and also the mountains around Cooke City have this recipe on some slopes. Eric was in Cooke City the last 2 days and found most slopes wind-scoured and only a few wind-loaded (<strong><a href="https://www.mtavalanche.com/images/19/wind-scoured-crown-butte">photo</…;). If wind drifts are not sitting on facets, they won’t avalanche. He found a mixed bag of conditions which he outlines in his <strong><a href="https://www.youtube.com/watch?v=d2uyqO9S4Qw&t=0s&list=PLXu5151n…;. In essence, snowpacks less than 3 feet deep are weak and could avalanche with a wind-load, while snowpacks that are deeper lack well-developed facets and are stronger (<strong><a href="https://www.mtavalanche.com/images/19/poor-structure-scotch-bonnet">pho…;). Dig, probe and be wary of slopes that are shallow and faceted. Today the avalanche danger is rated MODERATE.</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>, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u>), 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
January 16, 17 and 19 or 20, Intro to Avalanches w/ Field Day, Info and Register Here.
Avalanche on Lionhead Ridge
From a FB message:
"... on the way out if town in the truck we saw that Lionhead had a big slide before airplane hill. Must have been this morning because we didn't notice it yesterday."
Cracking and collapsing in Taylor Fork
From an email: "Lower elevation snowpack was a wallow through deep and unsupportable facets. We were sinking 12" - 18" on skis... straight to the ground off skis. Off the road, our sled tracks were dropping down almost to the ground.
At 8200'+ the snow was a bit more supportable. No collapsing, cracking, woomphing until...
We got to 8800' and were running out of time so decided to ski out. I was going to dig a pit on a 15 degree adjacent to a steeper pitch and as soon as I stepped out on to a more cohesive slab from the shallow snowpack I was on, the whole slope collapsed and shifted downhill a few inches (See photo). Didn't dig the pit... turned around, traversed to the trees, and slid home. Based pole and hand pit, the slab seemed to be about 1F - 4F over 18" - 24" Fist hardness facets.
The difference between the slope that collapsed and the rest of the tour was the slab. There had been recent windloading and the slab was more cohesive."
Skiers got this wind loaded slope to collapse and crack from an adjacent slope. A poor snow structure of facets underlying a harder wind slab was the culprit. Photo: D. Zinn
Forecast link: GNFAC Avalanche Forecast for Thu Jan 10, 2019GNFAC Avalanche Forecast for Fri Jan 11, 2019
GNFAC Avalanche Forecast for Wed Jan 9, 2019
<p>The southern mountains, including the Lionhead area has a weak snowpack. This weekend’s storm was large enough to create widespread instability and avalanches. A 1.5 foot thick layer of sugary facets on the ground is breaking in our stability tests (<strong><a href="https://www.mtavalanche.com/images/19/poor-structure-s-madison-range">p…;), and more importantly, with human triggers. Snowmobilers triggered multiple avalanches on Sunday (<u><strong><a href="https://www.mtavalanche.com/node/19607">details</a></strong></u>, <u><strong><a href="https://www.mtavalanche.com/images/19/lionhead-avalanche">photo</a></st…;) and again yesterday (<strong><a href="https://www.mtavalanche.com/images/19/snowmobiler-triggered-slide-lionh…;, <strong><a href="https://www.mtavalanche.com/node/19625">details</a></strong>), some from far away. Triggering slides is still likely given the overall weakness of the snowpack. Our field trips to Taylor Fork on Friday (<strong><a href="https://www.youtube.com/watch?v=l0aklSLqYaM&list=PLXu5151nmAvRNl9ku…;), Teepee Basin on Saturday (<strong><a href="https://www.youtube.com/watch?v=fXzzClQFS5s&list=PLXu5151nmAvRNl9ku…;), and Lionhead on Sunday (<strong><a href="https://www.youtube.com/watch?v=hugZzlbqGqg&index=4&list=PLXu51…;), were all unanimous in finding poor stability. Avoid riding or skiing in steep terrain and beware of triggering slides from below. For today the avalanche danger is rated CONSIDERABLE on all slopes.</p>
<p>Eric and his partner are in Cooke City and found strong winds had scoured most terrain (<strong><a href="https://www.mtavalanche.com/images/19/wind-scoured-crown-butte">photo</…;). They found a mixed bag of conditions with the deeper, 4+ foot snowpack being strong compared with slopes that have 3 feet or less, which are weak. These shallower areas have sugary facets at the ground which will likely avalanche when heavy snowfall returns someday (it is Cooke City after all). The danger is dropping yet triggering avalanches is still possible because of this variability in the snowpack. The only way to know what is under your sled or skis is to dig. For today the avalanche danger is rated MODERATE on all slopes.</p>
<p>The mountains around Bozeman and Big Sky have not gotten significant snowfall in 10 days, yet people are still getting collapsing, cracking and triggering avalanches as recently as Sunday. An <strong><a href="https://www.mtavalanche.com/node/19596">avalanche on Ross Peak</a></strong>, a small avalanche <strong><a href="https://www.mtavalanche.com/node/19598">triggered in Beehive</a></strong>, and <strong><a href="https://www.mtavalanche.com/node/19599">collapsing and cracking on Mt. Ellis</a></strong> are 3 of the most recent red flags. On Saturday, a snowmobiler triggered a 2 foot deep hard slab avalanche near Ross Peak that Alex investigated (<strong><a href="https://www.mtavalanche.com/node/19583">details</a></strong>). The wind-loading was fierce, even as Alex was being filmed (<strong><a href="https://www.youtube.com/watch?v=EVCMgc_z3wA&t=0s&list=PLXu5151n…;), and his video shows us the persistent weak layer we are faced with, a 1.5 foot thick layer of facets at the ground.</p>
<p>All the reported activity is on these facets which is not getting stronger anytime soon. Collapsing and cracking are evidence that our weight is initiating and propagating fractures on this layer and is bulls-eye information that the slope is unstable. There is no need to dig; cracking and collapsing are free stability tests. For today, avalanches are still possible and the danger is rated MODERATE.</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>, email (<u><a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a></u>), 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
TONIGHT! January 9, 1-hr Avalanche Awareness, 7-8 p.m. Spire Climbing Center, Bozeman.
Snowmobiler triggered slide in Lionhead
A snowmobiler triggered this small, but deep avalanche as he rode under the slope.
From his email, "We were riding as a group of 5. All with beacons ,shovels, probes and 4 with inflate packs. The hill broke as I was side hilling. I was just ahead of it and not knocked off the sled."