Sunday, January 27th, 2008 Good morning. This is Scott Schmidt with the Gallatin National Forest Avalanche Advisory issued on Sunday, January 27, at 7:30 a.m. The Gallatin Valley Snowmobile Association, in cooperation with the Friends of the Avalanche Center, sponsor todays advisory. This advisory does not apply to operating ski areas. MOUNTAIN WEATHER Three to four inches of new snow has fallen in the mountains around West Yellowstone and Cooke City this morning. Winds have been 20 40 mph from the southwest at all elevations, and morning temperatures are in the mid-teens at 9000 feet. A strong system moving into the area from the southwest will produce mountain showers today, with heavy snowfall in the southern mountains starting tonight. By tomorrow morning, 6 8 inches of snow will accumulate in the mountains around West Yellowstone and Cooke City. Two to four inches will fall in the mountains around Big Sky, with a trace to 2 inches in the mountains near Bozeman. Winds will continue to blow 20 45 mph from the southwest, and mountain temperatures will be in the mid-20s at 9000 feet. SNOWPACK AND AVALANCHE DISCUSSION The northern Gallatin and northern Madison Ranges: The Moonlight Basin ski patrol released a large avalanche on a north facing, wind-loaded slope yesterday. This avalanche released on well developed facets near the ground. Natural activity was also reported on a recently wind-loaded, east facing slope on Fan Mountain, and on a southwest facing slope below Beehive Peak. I was on Buck Creek Ridge yesterday. Strong southerly winds were producing sensitive wind slabs on north-facing slopes that would fracture and propagate with the added weight of a snowmachine. These slabs were running on the old snow surface and did not break into older layers. I also investigated an avalanche that was triggered by a snowmobiler on Wednesday. This slide occurred on a southeast facing slope and ran on the layer of faceted crystals near the ground that has produced human-triggered avalanches on all aspects in the mountains near Big Sky for the past month. All steep slopes in the northern Gallatin and northern Madison Ranges should be approached with caution. A CONSIDERABLE avalanche danger exists on all wind-loaded slopes, and on non-wind-loaded slopes steeper than 35 degrees. Non-wind-loaded slopes that are less steep have a MODERATE danger. The southern Madison and southern Gallatin Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City, and the Washburn Range: A layer of faceted snow sitting on an icy crust is buried 2 3 feet deep in the mountains around Cooke City and West Yellowstone. A snowmobiler triggered an avalanche on this layer in the mountains near West Yellowstone Wednesday, and both human-triggered and natural avalanches were reported in the Cooke City area Thursday. Strong winds and new snow will continue to produce unstable conditions on all wind-loaded slopes which have a CONSIDERABLE avalanche danger. Non-wind-loaded slopes in these mountains have a MODERATE danger. The Bridger Range: A group skiing on Ross Peak in the Bridger Range dug several snowpits and reported good snowpack stability. They experienced no cracking or collapsing of the snowpack on their approach to the chute they intended to ski. Once they started their decent, they encountered small wind-slabs that released easily but present no hazard. The Bridger Bowl ski patrol used large explosives to released wind slabs 2 feet deep near the ridge crest. These avalanches involved wind deposited snow from the past several days and ran on the old snow surface. Wind-loaded slopes in the Bridger Range continue to be the avalanche concern and have a CONSIDERABLE danger if they are steeper than 35 degrees. Wind-loaded slopes that are less steep have a MODERATE danger. All non-wind-loaded slopes have a LOW danger. HEADS UP! A layer of surface hoar and near-surface facets has been buried by a few inches of snow on many slopes in southwest Montana. These layers may result in unstable conditions as more snow accumulates.