Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Wednesday, December 19 at 7:30 a.m. Today’s advisory is sponsored by Lone Peak Brewery and Bountiful Table. This advisory does not apply to operating ski areas.
Under clear skies mountain temperatures are zero to minus five with light westerly winds. There’s no new snow to report, the first time in 14 days. Today will be sunny with temperatures rising into the low teens. Winds will blow 10-20 mph out of the west, but become stronger from the southwest tonight. A high pressure system will keep skies clear and dry for the next two days.
Bridger Range Madison Range Gallatin Range
Lionhead area near West Yellowstone Cooke City
Finally, the snowpack gets a breather. A day without snowfall and strong winds has been rare; not that I’m complaining! Our snowpack is looking manageable so far. Weak layers of facets can be found near the ground on many slopes, but they are a problem on only a few. Our stability tests are showing increased strength and even more telling, with 14 days of snow load there have been hardly any avalanches. Even though steady and moderate snowfall has promoted stability, I still have two avalanche concerns today:
- Wind-loaded slopes. Wind drifted, soft slab avalanches were triggered near ridgelines in the Bridger Range (photo). Wind drifts also naturally released in gullies near Cooke City (photo). Backcountry slopes with a wind-load were sensitive yesterday, but I expect them to be stubborn on lower-angled terrain today (less than 35 degrees).
- Persistent weak layer. On a handful of slopes we are still getting unstable results in our snowpit tests due to poor snow structure (snowpit profile). There does not seem to be a common aspect associated with this, but a weak layer of angular facets is in the bottom one and a half feet of the snowpack. We have not seen, nor heard reports of recent signs of instability on this deep layer (i.e. collapsing, cracking or avalanches) outside of ski area explosives. However, crack propagation in our tests is a condition of instability and we do not throw these results out, we pay attention to them. The Extended Column Test (video tutorial) is a reliable way to test the snow.
Given the avalanche concerns associated with recent wind-loading along with a smattering of slopes that have poor snow structure, it’s still possible to trigger avalanches today. For this reason I’m rating the avalanche danger MODERATE on all slopes.
Mark will issue the next advisory tomorrow morning at 7:30 a.m. If you have any snowpack or avalanche observations drop us a line at mtavalanche@gmail.com or call us at 587-6984.
TOMORROW: Snowmobiler Introduction to Avalanches with Field Course in West Yellowstone on December 20 and 21. Sign up for this class HERE.
Free 1-hour Avalanche Awareness lecture at Bridger Bowl at 1 p.m. on the 4th floor of the Saddle Peak Lodge on December 23. No registration necessary.