Monday, February 25th, 2008 Good morning. This is Scott Schmidt with the Gallatin National Forest Avalanche Advisory issued on Monday, February 25th, at 7:30 a.m. Sweet Peas Nursery, in cooperation with the Friends of the Avalanche Center, sponsor todays advisory. This advisory does not apply to operating ski areas. MOUNTAIN WEATHER Two to four inches of snow has fallen in most the mountains of southwest Montana during the past 24 hours. The exception is the mountains near Big Sky, which have received 4 7 inches. Winds have been 10 15 mph from the southwest, and morning temperatures are in the upper teens at 9000 feet. Snow will continue today, with accumulations of 2 inches in the mountains near West Yellowstone and Cooke City, and 2 4 inches in the mountains near Bozeman and Big Sky. Winds have shifted northwest and will blow 10 20 mph at the ridgetops, with mountain temperatures in the mid-20s at upper elevations. SNOWPACK AND AVALANCHE DISCUSSION The Bridger Range: I was in the northern Bridger Range yesterday. My partner and I dug on a wind-loaded slope at found the layer of weak snow that we have been discussing in the advisory for the past week. This layer is buried 12 18 inches beneath the surface and produces relatively clean shears with moderate force during stability tests. While it is possible this layer could produce an avalanche, we felt it was unlikely and it did not prevent us from traveling up, across, and down steep slopes. A more pressing concern is the lack of bonding between yesterdays new snow and the hard, icy surface it has been deposited on. This new snow sloughed easily when we skied steeper terrain and will likely produce slab avalanche on wind-loaded slopes if the winds start to blow. Winds have been uncharacteristically calm in the Bridger Range since this storm started so for today, the avalanche danger remains MODERATE on wind-loaded slopes steeper then 35 degrees. All other slopes in this mountain range have a LOW danger. The northern Gallatin and northern Madison Ranges: There is good news and bad news from the northern Gallatin Range. One of our regular observers was in the Hyalite area and found the snow to be supportable and well bonded through the depth of the snowpack. This is significant because these mountains have been plagued by a thin, weak snowpack for most of the winter. Doug went to Mt Blackmore yesterday and found similar bonding with no deeply buried weak layers of concern. That is the good news, now for the bad. A weak layer of surface snow formed as a result of the clear weather we have experienced and this layer is now buried 2 4 inches deep. Ill let Doug explain the consequence of this buried weakness in another of his Oscar winning YouTube performances. http://www.youtube.com/watch?v=u7z9iiFf2bY For those of you in our listening audience, Doug found this layer produced clean shears with only an inch of snow for a load. He and his partner saw two natural avalanches on slopes that had been loaded by recent winds, and experienced shooting cracks that propagated up to 40 feet as they traversed a low angle slope. This layer will become more active as snow is piled on it, and wind-loaded slopes will be extremely sensitive. Mark did not find this layer in the northern Madison Range last Wednesday but it may have formed in the days after his visit. Dig down and look for this layer before starting onto any steep terrain, especially if it is being wind-loaded. The avalanche danger in the northern Gallatin and northern Madison Ranges is CONSIDERABLE on recently wind-loaded slopes steeper then 35 degrees and MODERATE elsewhere. The southern Madison and southern Gallatin Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City, and the Washburn Range: The southern mountains near West Yellowstone and Cooke City received 2 4 inches of snow yesterday. Based on observations from last week, it is unlikely that this snow has been deposited on weak surface snow. As with the Bridger Range, the concern will be how well the new snow bonds to the old snow surface. Winds have been relatively calm in these mountains so new wind-deposits will be small but are likely to release with very little added force. The resulting avalanche may not be big, but the consequences could be significant if the slide carries you over a cliff or through trees. In addition, wind-loaded slopes at elevations above treeline have produced avalanche in the past week and should be avoided. The avalanche danger in the southern Madison and southern Gallatin Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City, and the Washburn Range remains MODERATE on slopes steeper then 35 degree. All other slopes have a LOW danger. HEADS UP If winds unexpectedly increase to the point that snow is being transported today, the avalanche danger will be on the rise. Steep slopes where wind is depositing snow will likely avalanche and should be approached with caution.