Good morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Sunday, December 28 at 7:30 a.m. The Montana Telemark Corporation, in cooperation with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.
Strong winds will be the main weather event today. At 4 a.m. ridgetop winds were blowing 20-40 mph from the west in the Bridger Range and southwest elsewhere. Temperatures were in the upper teens except near West Yellowstone where they were in the upper single digits. Since yesterday morning a trace to 1 inch of snow accumulated near Bozeman, Big Sky and Cooke City, and these areas should get an additional 1-2 inches by tomorrow morning. 4-5 inches of snow accumulated near West Yellowstone and the southern Madison Range since yesterday. These areas should receive 3-4 inches by tomorrow morning. Temperatures at 9000ft will be in the low 20’s F and winds will blow 30-40 mph from the west-southwest with gusts in the 50’s.
The southern Gallatin Range, the entire Madison Range, the mountains near West Yellowstone and the Lionhead Area, the mountains near Cooke City, and the Washburn Range:
Natural and human triggered avalanches have been reported throughout the advisory area. A group of snowmobilers in the southern Madison Range was riding in relatively flat terrain and triggered an avalanche which fractured on steep slopes above them. One of the riders was nearly caught, and they recorded an excellent video clip you can see at:
http://www.youtube.com/watch?v=70cXXQ_XtJs
One human triggered avalanche near West Yellowstone was notable because it occurred on a 33 degree slope. In addition to avalanche activity, we been seeing many obvious signs of instability in the snowpack such collapsing and cracking. You can see several photos of cracking and avalanche activity at:
http://www.mtavalanche.com/photos/photos.php
There have been too many avalanches to report the specifics of each, but this fact alone should be a clear warning sign. These avalanches have been sliding on faceted snow near the ground, and frequently have occurred in areas where these facets exist near an ice crust found about 1 foot above the ground. Near Cooke City, this facet/crust combo can be found on many popular slopes. Near West Yellowstone, one group of skiers found considerable variability and described the snowpack as “very spooky…in generally safe areas.” For today, a HIGH avalanche danger exists on all wind loaded slopes and a CONSIDERABLE avalanche danger exists on non-wind loaded slopes.
The Bridger and northern Gallatin Ranges,
The Bridger and northern Gallatin Ranges have similar instabilities but have received less snow. These areas have seen strong winds that formed wind slabs which slid yesterday. A group of skiers in the southern Bridgers found a thin and weak snowpack. They saw a recent avalanche and experienced collapsing and cracking. With warmer temperatures and little snow left to be blown by today’s winds, I do not expect widespread natural avalanche activity. For today, I definitely expect human triggered avalanches on recently wind loaded slopes which have CONSIDERABLE avalanche danger. Non wind-loaded slopes have a MODERATE danger.
SIDE NOTE
Thank you to everyone for sending us excellent observations. These have been very helpful. Everyone skiing and riding in the backcountry seems to be carefully assessing the snowpack and making conservative decisions. Keep up the good work.
I will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry give us a call or send us an email with your observations. You can reach us at 587-6984 or at mtavalanche@gmail.com.
