Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Tuesday, December 18 at 7:30 a.m. Today’s advisory is sponsored by Gallatin County Search and Rescue in partnership with the Friends of the Avalanche Center. This advisory does not apply to ski areas.
Since 5 a.m. yesterday morning the mountains picked up 3-4 inches of snow, with Cooke City getting eight inches. Winds are blowing 20-30 mph out of the west, a decrease from yesterday’s gusts that hit 50-60 mph. Mountain temperatures are in the chilly single digits. Today will be partly cloudy with only slight warming. Winds will continue out of the west, but become light. Scattered snow flurries will drop a trace to one inch of new snow by morning. Overall it’s a cold, calm, winter day.
Bridger Range Madison Range Gallatin Range
Lionhead area near West Yellowstone Cooke City
I found all the snow that was supposed to fall in Colorado. It’s in Cooke City! Mark and I dug three pits to the ground, one as deep as seven feet (video). Our most shallow pit came in at four feet deep, which was also our weakest, but more about that in a second.
Daily snowfall has blanketed southwest Montana over the last 20 days. Winds have been strong, gusty and created wind drifts, most notably at the higher elevation ridge lines where avalanches are likely to be triggered. Ski patrols on Lone Peak were able to trigger these wind-loaded slopes, and a sledder on Sunday noted natural avalanche activity from wind-loading on Buck Ridge south of Big Sky as well.
Talking to snowmobilers yesterday I condensed the entire advisory into one sentence: Besides wind-loaded slopes, the stability is pretty good. This assessment seems accurate for our entire area. I do not expect folks to trigger avalanches from a distance, nor do I expect a widespread avalanche cycle in the coming days. You can ride and ski most slopes without consequence. But nothing’s perfect, and that goes for our snowpack too. The shallow pit Mark and I dug on the south side of Henderson Mountain illustrates this well. A layer of weak snow (facets) near the ground was breaking clean in our tests (ECTP21, Q1; snowpit). We’ve gotten similar results in the Madison, Gallatin and Bridger Ranges, but only on a handful of slopes. With the latest round of storms we have not seen natural or human triggered avalanches on this layer, but we will continue to monitor it. On Sunday, Moonlight Basin was able to trigger a wind-loaded slope with big explosives that stepped down to this weaker snow. The avalanche was large and reminds me that even relatively strong facets can still avalanche.
Mark and I stayed clear of wind-loaded slopes and skied lines that were not very exposed. Triggering wind drifts could step down to deeper layers on select, but not easily identifiable slopes. Dig and test. For today, the avalanche danger continues to be rated CONSIDERABLE on all wind-loaded terrain. All other slopes have a MODERATE danger.
I 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.
Interested in more snowpack data? Check out the snowpit page for recent profiles from around the area. Snowpit Profiles
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.