Archived Advisory for Thu Jan 24 2008

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24 January 2008

Good morning. This is Ron Johnson with the Gallatin National Forest Avalanche Advisory issued on Thursday, January 24, at 7:30 a.m. Sweet Pea Landscaping, in cooperation with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.

MOUNTAIN WEATHER

No snow fell during the past 24 hours. This morning at 4:00 a.m., mountain temperatures were in the low teens F and southwesterly ridgetop winds were 10-20 mph near Big Sky. In the Bridger Range westerly ridgetop winds were 20-30 mph. Today a high pressure ridge will produce clear to partly cloudy skies, mountain temperatures will reach the 20’s and west-southwesterly ridgetop winds will blow 15-25 mph. Tonight a weather disturbance will bring moisture into southwest Montana. By tomorrow, 1-3 inches of new snow will accumulate in the mountains around West Yellowstone. Less than 2 inches will fall in other mountain areas of southwest Montana.

SNOWPACK AND AVALANCHE DISCUSSION

The Bridger Range:

Tuesday evening 8 inches of low density snow fell in the Bridger Range. Yesterday this snow was blown onto the lee side of ridges and gullies. The resulting wind slabs will fracture on underlying low density snow. This was the case in the northern Bridger Range on Tuesday when skiers saw an avalanche naturally release on a steep wind-loaded slope. Today a CONSIDERABLE avalanche danger exists on all wind-loaded slopes. Non wind-loaded slopes steeper than 35 degrees have a MODERATE danger. A LOW danger exists on low angles non wind-loaded slopes.

The Gallatin Range and Madison Ranges:

Recently wind-loaded slopes in the mountains around Big Sky continue to produce avalanches. Yesterday ski patrollers at Big Sky released several wind slabs with ski cuts and explosives. They also saw several naturally released avalanches in the surrounding backcountry. These avalanches released on southerly facing slopes that had been wind loaded from north-northwesterly winds, which blew earlier this week. Yesterday a skier triggered a non wind-loaded slope near Big Sky. They were not caught in the avalanche, which fractured on a south facing, 34 degree steep slope. The weak layer was faceted snow located 6 inches above the ground. A layer of faceted snow near the ground especially on south facing slopes and wind slabs deposited on low density snow continue to plague the snowpack in the Gallatin and Madison Ranges. Therefore, a thoughtful assessment of snow stability is warranted on all slopes. Today a CONSIDERABLE avalanche danger exists on all wind-loaded slopes and on non wind-loaded slopes steeper than 35 degrees. The avalanche danger on all other slopes is MODERATE.

The Lionhead area near West Yellowstone, the mountains around Cooke City, and the Washburn Range:

Yesterday, Doug Chabot and Mark Staples buzzed around Lionhead on snowmobiles. They saw several avalanches including one that was triggered by a snowmobiler on Tuesday. Photos of some of the avalanches are posted at: http://www.mtavalanche.com/photos/photos.php

These avalanches fractured on a layer of small grained faceted snow on a thin ice crust located 1-2 feet above the ground. A similar layer of faceted snow without an associated ice crust exists was exposed in snowpits dug by skiers earlier this week in the mountains around West Yellowstone. Doug recently found similar layers in the mountains around Cooke City. Many folks are finding stable slopes to play on, but the existence of a weak layer poised to fracture on recently wind-loaded slopes means a CONSIDERABLE danger exists on these slopes. A MODERATE danger exists on all non wind-loaded slopes.

Mark Staples will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry give us a call or email with your observations. You can reach us at 587-6984 or email us at mtavalanche@gmail.com .

AVALANCHE EDUCATION

Tuesday, January 29th, Angela Patnode will present a free 1-hour Avalanche Awareness Class for women at 7:00pm at the Bozeman Public Library in the small conference room. This class is sponsored by Bozeman-based Team WinS (Women in Sports). For more information visit www.teamwins.org