Good morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Friday, December 7 at 7:30 a.m. Today’s advisory is sponsored by Bridger Bowl in partnership with the Friends of the Avalanche Center. Bridger Bowl opens today and uphill travel within its boundaries is no longer permitted.
Overnight the northern Madison and northern Gallatin Ranges and the mountains around Cooke City received 7-10 inches low density snow (5% density). The Bridger Range received 5 inches. The mountains near West Yellowstone including the southern Madison and southern Gallatin Ranges received 1-2 inches. This morning temperatures were mostly in the low to mid-teens F and westerly winds were averaging 15-20 mph with gusts of 30 mph. In Hyalite Canyon winds were averaging 28 mph and gusting to 50 mph.
A few more inches of snow should fall this morning. Today temperatures will struggle to reach the low 20s F and westerly winds will continue blowing 15-30 mph. Snowfall will return this evening with similar amounts as last night if not more. This weather pattern has a slight NW flow and more energy associated with it than last night. I don’t think this pattern will favor the Bridger Range more than other areas….but there’s a chance. By tomorrow morning most places should get 8-12 inches of new snow.
Bridger Range Northern Madison Range Northern Gallatin Range
Last night’s new snow was easily transported by westerly winds and formed fresh wind slabs. These fresh winds slabs will be the primary avalanche problem today. Avoid wind loaded areas and you can avoid most avalanches today.
There is one other potential problem. Yesterday, I dug snowpits with the Yellowstone Club Ski Patrol. We found a strong snowpack on a NNE aspect at 9300ft. There was some weak, faceted snow at the ground but it was unreactive in our stability tests. In isolated areas these facets are much weaker and can produce avalanches. A good example of this potential is an avalanche that was triggered last weekend on Buck Ridge just south of Big Sky on a slope with almost the same aspect and elevation. This avalanche was remotely triggered from a low angle slope and propagated 700ft across a heavily wind loaded area (video, pictures, snowpit).
The mountains near Cooke City also have fresh wind slabs that will easily produce avalanches. However, these mountains have received substantial snow for eight of the last nine days (5.1 inches of SWE since Nov 28). To put it in perspective, these mountains received more snow in the last nine days than Hyalite Canyon near Bozeman has received in the last 45 days. This snowfall has added a lot of weight to the snowpack. Even though the snowpack is generally strong, it needs time to adjust to this loading, and I would be very conservative in my terrain choices today.
For today, all wind loaded slopes have a CONSIDERABLE avalanche danger. All other slopes have a MODERATE avalanche danger.
Southern Madison Range Southern Gallatin Range
Lionhead area near West Yellowstone
The southern Madison and southern Gallatin Ranges and the mountains near West Yellowstone only received 1-2 inches of snow overnight. With less snow there will be fewer avalanches, but there are a few things to consider.
- Avalanches involving fresh wind slabs are possible near ridgelines and cross loaded gullies.
- The snowpack is mostly strong, but a few slopes contain buried surface hoar. On Wednesday I found this weak layer in the Taylor Fork area (photo, video). Either dig snowpits and look for this layer or assume it exists on every slope.
For today avalanches are possible and heightened avalanche conditions exist in some areas and the avalanche danger is rated MODERATE.
ICE CLIMBERS: Hyalite Canyon is part of the Northern Gallatin Range where 10 inches of low density snow fell overnight. Our Hyalite weather station (video about this station, and see data here) on top of Flanders Mountain was recording winds averaging 28 mph with 52 mph gusts at 6 a.m. These winds easily transported last night’s new snow and formed fresh wind slabs. Additionally the new snow fell on a smooth and icy snow surface which will allow sloughs and wind slabs to run far and fast..
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.
Snowmobiler Introduction to Avalanches at Greenup Performance in Black Eagle near Great Falls, MT, TOMORROW, December 8, 9 a.m. to 2 p.m. FREE. No sign up required!
Snowmobiler Introduction to Avalanches with Field Course in Billings at Hi-Tech Motor Sports on December 12 and 13, 6-9 p.m. and the field course on January 20 in Cooke City. Sign up for this class HERE
Snowmobiler Introduction to Avalanches with Field Course in West Yellowstone on December 20 and 21. Sign up for this class HERE.
FREE 1 hour lectures:
December 12, REI in Bozeman, 6:30 p.m.