GNFAC Avalanche Forecast for Tue Feb 5, 2019
<p>Snowfall has slowed down and yesterday’s avalanche warning has expired. However, conditions remain very unstable, especially on wind loaded slopes. Over the last 48 hours, more than a foot of heavy snow (1.3-1.9” of <a href="https://www.nrcs.usda.gov/wps/portal/nrcs/detail/or/snow/?cid=nrcs142p2… water equivalent</a>) fell in the southern ranges. South and southwest winds have created even thicker slabs (2-3’ deep) on windloaded slopes.</p>
<p>On Sunday, I found a layer of surface hoar underneath the new snow in the southern Madison Range (<strong><a href="https://www.youtube.com/watch?v=8U0I_ZNd8pU&t=0s&index=2&li…;). Yesterday, Snow Rangers found it in the Lionhead area, now buried by 1.5’ of new snow (<a href="https://www.mtavalanche.com/images/19/unstable-tests-lionhead">photo</a…;). New snow falling on surface hoar makes for touchy conditions, you can trigger avalanches from below or on lower angled slopes. In addition, you can’t forget about the weak snow lower in the snowpack. Deep and wide avalanches could break on these weak layers (<strong><a href="https://www.mtavalanche.com/images/19/large-avalanche-near-lionhead">ph…;, <strong><a href="https://www.mtavalanche.com/images/19/avalanches-breaking-weak-snowpack…;). Give the snowpack time to adjust to the weight of new snow by avoiding avalanche terrain today. On wind-loaded slopes, large natural avalanches are likely and the avalanche danger is HIGH. On other slopes, human triggered avalanches are likely and the avalanche danger is CONSIDERABLE.</p>
<p>Near Cooke City and Big Sky, storm snowfall totals are 10-13” (1.0-1.2” of SWE). The combination of new snow and moderate south-southwest winds formed 1-2’ thick drifts and make avalanches easy to trigger. On some slopes, the new snow fell onto a strong snowpack and avalanches within the new snow are the primary concern. On other slopes, the new snow fell onto a weak, shallow, snowpack, and avalanches could break 2-3’ deep, propagating across the whole slope. Careful snowpack assessment is required to determine which situation you are dealing with. Eric’s video from yesterday in the northern Madison Range highlights the big variations that exist over small distances (<a href="https://www.youtube.com/watch?v=kbvE5YGGJOQ&index=2&list=PLXu51…;). While the snowpack is working to accommodate the new load, steer clear of new wind drifts and any slope with weak snow near the ground. If in doubt, keep it simple by sticking to low angled slopes. The avalanche danger is CONSIDERABLE.</p>
<p>The mountains near Bozeman have only received 4-6” out of this storm so far. On Sunday, Alex found small fresh drifts of snow were easy to trigger in the northern Bridger Range (<strong><a href="https://www.youtube.com/watch?v=xO15cidZK20&t=0s&index=4&li…;). You could trigger similar avalanches today. A less likely, but higher consequence possibility is triggering an avalanche on weak layers buried deeper in the pack. These weak layers are most prevalent in shallower areas, such as Mt. Ellis (<strong><a href="https://www.youtube.com/watch?v=Z0dOv0z4GDI&t=0s&list=PLXu5151n…;, <a href="https://www.mtavalanche.com/node/19903">avalanche incident</a></strong>) and the <a href="https://www.mtavalanche.com/node/19808">West side of the Bridgers</a>, but it’s worth your time to dig down to look for and assess these layers before committing to any steep slope. The avalanche danger is MODERATE.</p>
<p>If you get out and have any avalanche or snowpack observations to share, contact us via our <a href="https://www.mtavalanche.com/node/add/snow_observation">website</a>, email (<a href="mailto:mtavalanche@gmail.com">mtavalanche@gmail.com</a>), phone (406-587-6984), or Instagram (#gnfacobs).</p>
<p>The Backcountry Avalanche Warning continues today for the Centennial Range of Idaho. Heavy snow and wind are loading a weak snowpack. Natural and human triggered avalanches are likely. Avalanche terrain and avalanche runout zones should be avoided. Very dangerous avalanche conditions exist and avalanche danger is HIGH on all slopes. </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!, Sidecountry Specific Avalanche Awareness for Friends and Family, 6-7p.m. at Story Mill Community Park.
February 6, 1-hr Women’s Avalanche Awareness, 6-7p.m. at REI Bozeman.
Weather and Avalanche Log for Tue Feb 5, 2019
Avalanche Warning Centennials
Snowmobilers in the Lionhead area got unstable test results, easily propagating fractures in ECT tests on a weak layer buried about 50 cm deep. Photo: J. Norlander
Multiple large avalanches in Centennials and Lionhead
From e-mail on 2/1/19: "The Reas Peak area had 7 slides that I could see from the bottom of the drainage, most of them looked to have occurred with the last storm and had a northerly influence to their aspect. The largest and most recent slide I included in the [above photo], Reas Peak is the highest peak on the left in the photo and the slide path is on a NE aspect. If you look close at the photo you can see a 2-3’ crown on the far left side of the frame on the north aspect of Reas from another slide."
Another observer saw a large slide near Lionhead (photo) and one on Reas Peak from the same cycle.
This photo was taken by a FS snow ranger on Feb 1st. These avalanches likely occurred towards the end of a period of steady snowfall from Jan 16th to 28th. From e-mail: "The Reas Peak area had 7 slides that I could see from the bottom of the drainage, most of them looked to have occurred with the last storm and had a northerly influence to their aspect. The largest and most recent slide I included in the [above photo], Reas Peak is the highest peak on the left in the photo and the slide path is on a NE aspect.
This photo of an avalanche on the north side of Reas Peak was taken by a FS snow ranger on Friday, Feb 1. It likely occurred towards the end of a period of steady snowfall from January 16th to 28th. Photo: C. Hericks