Good morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Saturday, March 21, at 7:30 a.m. Mystery Ranch in partnership with the Friends of the Avalanche Center sponsors today’s advisory. This advisory does not apply to operating ski areas.
This morning temperatures were in the mid to upper 30s F under clear but warm skies. Cooke City was the only place with mountain temperatures below freezing. Winds were blowing 10-25 mph from the SW. Today temperatures should again rise into the 40s F. Winds will increase some and blow 15-30 mph from the SW. Some clouds should arrive by afternoon and may deliver a trace of precipitation tonight.
Bridger Range Madison Range Gallatin Range
Lionhead Area near West Yellowstone Cooke City
The last two days helped the snowpack transition to spring by warming during the day and refreezing at night. Refreezing at night limits wet snow avalanche activity. What will happen today is hard to predict. Without freezing last night (except near Cooke City) and with relatively warm skies, the snowpack shouldn’t need much heat this morning to soften quickly. The worst time for wet avalanches is the first major warm up of the snowpack which happened last weekend. There should be some wet, loose avalanches today, but they shouldn’t be too big and mainly involve the few inches of snow that fell mid-week. Cornices, some large ones, may fall and are worth watching for as Eric found on Thursday (video, photo) in Hyalite Canyon.
An isolated but interesting problem is a faceted layer capped by a wind slab that caused an avalanche on Thursday in the northern Bridger Range on a NE aspect near 8500 feet. It was 6-10 inches deep, 50 feet wide, and over 200 feet downhill. These facets formed during a brief period of cold clear weather possibly Wednesday night. Then, strong winds Thursday morning capped this layer with a cohesive wind slab. Watch this video of the avalanche being triggered. Yesterday my partner and I looked at this slide and wondered if we could still trigger similar avalanches. When we triggered piece of hangfire (remaining slab that didn’t slide originally) 20 feet wide, our question was answered with a clear YES.
Today, watch for wet avalanches mostly on southerly aspects. On higher elevation northerly aspects with dry snow, watch for wind slabs that may be sitting on facets. While this problem may only exists in the northern Bridger Range, there’s a decent chance it could be in other areas. With a few avalanche problems today in specific terrain, the avalanche danger is rated MODERATE.
Eric 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.