Good Morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Friday, December 10, at 7:30 a.m. Bridger Bowl, in cooperation with the Friends of the Avalanche Center, sponsors today’s advisory. This advisory does not apply to operating ski areas.
This morning temperatures were near 20 degrees F, and winds were ripping 20-40 mph from the SW except on Flanders Mountain in Hyalite where they were blowing 40-60 mph. Yesterday the mountains near Cooke City and West Yellowstone received 1-2 inches of snow and all other areas remained dry or received a trace snow. A strong pulse of snowfall will come this morning followed by decreasing temperatures although the coldest air will descend into eastern Montana. Strong winds will continue blowing 20-40 mph from the W, and temperatures will drop into the low teens F by late this afternoon. By tomorrow morning 4-6 inches of snow will accumulate in most areas.
The Bridger, Gallatin and Madison Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range:
Last weekend widespread surface hoar was observed in all areas from valley bottoms to ridgetops, but it was destroyed this week on some slopes by wind and/or sun. While surface hoar was stuggling to survive this week, the snow surface was getting worked and becoming faceted by the combination of warm sunny days and cold nights. The crux is that some slopes, especially ones below treeline, warmed enough to destroy any facets or surface hoar as on observer found south of Cooke City. At the same time, the surface snow on other slopes became weaker and faceted as the Big Sky Ski Patrol observed yesterday on Lone Mountain where even wind slabs started faceting. Fortunately, these weak layers are not buried deeply and hunting for them can be done quickly with shallow hasty pits. The main concern today is any area with wind-blown snow which may rest on surface hoar and/or near-surface facets.
Weak faceted snow exists near the ground on the west side of the Bridger Range, where a group of skiers found a supportable slab resting on top of 4-8” of facets at the ground. They said this layer will not support a load of new snow or wind deposited snow and would produce avalanches. The Moonlight Basin Ski Patrol tested their Headwaters terrain for the first time yesterday and was able to trigger one avalanche (photo) that broke near the ground. Although many areas do not have these facets, we are continually reminded of the need look for them before committing to a slope.
Strong winds (photo) forming fresh wind slabs continue to be the primary avalanche problem today. Wind slabs have formed mostly near ridge lines but will be found at lower elevations today and may surprise you. With buried surface hoar or other faceted crystals, even slightly wind affected snow can be slabby enough to produce an avalanche. For today, the avalanche danger is rated CONSIDERABLE on all wind loaded slopes and MODERATE everywhere else.
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.
Upcoming Avalanche Education
“How Much Did It Snow?” Join Lucas Zukiewicz from the Montana Snow Survey for a FREE presentation/discussion on the SNOTEL system in SW Montana. The discussion will cover how to access SNOTEL information and interpret the data for snow and weather conditions. Tomorrow - Saturday, December 11, 7:30pm – 8:30pm at World Boards.
Avalanche Awareness for Snowmobilers in West Yellowstone Thursday, December 16th from 12 p.m. to 5 p.m (lectures), with an all day field day Friday, December 17th. For more information check out http://www.mtavalanche.com/education/classes/snowmobilers or call us at 587-6984.
Other News
This year REI has chosen Friends of GNFAC as their charity of choice. By making a donation through REI you can help The Friends continue to support the Avalanche Center and promote avalanche education throughout southwest MT.