5 January 2007

 Good morning. This is Ron Johnson with the Gallatin National Forest
 Avalanche Advisory issued on Saturday, January 5, at 7:30 a.m. Yamaha
 and Team Bozeman, in cooperation with the Friends of the Avalanche
 Center, sponsor todays advisory. This advisory does not apply to
 operating ski areas.


 MOUNTAIN WEATHER

 Overnight the mountains around West Yellowstone got pummeled with 6-10
 inches of new snow. The mountains around Cooke City got 2-4 inches. No
 snow accumulated in the mountains around Big Sky or Bozeman.

 Southwesterly ridgetop winds have ripped along at 30-60 mph. Today
 ridgetop winds will switch to the west and blow 20-40 mph. Moist,
 unstable air combined with the passage of a cold front through
 southwest Montana will produce 4-6 inches of new snow in the mountains
 around West Yellowstone and Cooke City. The mountains around Big Sky
 and Bozeman could get 1-3 inches. This morning, mountain temperatures
 were in the low 20s to low 30s F. By this evening, they will cool to
 the teens to 20s F.


 SNOWPACK AND AVALANCHE DISCUSSION

 The southern Gallatin and southern Madison Ranges, including the
 Lionhead area near West Yellowstone:

 Yesterday Karl Birkeland and fellow snow scientists were on Lionhead
 near West Yellowstone. They found the weakest snow in the snowpack was
 a layer of faceted snow near the snow surface. They concluded
 their snow studies prior to the onslaught of new snow and strong
 winds. The weak layer of faceted snow is now buried at least
 6-10 inches deep on non wind-loaded slopes and perhaps 1-2 feet deep
 on wind-loaded slopes. This load of new snow was added to the snowpack
 in only a few hours. The faceted snow will probably succumb to the
 added stress and avalanches are likely. Today a HIGH avalanche danger
 exists on wind-loaded slopes steeper than 35 degrees. Less steep
 wind-loaded slopes have a CONSIDERABLE avalanche danger. A
 CONSIDERABLE avalanche danger also exists on non wind-loaded slopes
 steeper than 35 degrees, while less steep non wind-loaded slopes have
 a MODERATE danger.


 The mountains around Cooke City, and the Washburn Range:

 The 2-4 inches of snow that fell overnight in the mountains around
 Cooke City were deposited on a snowpack that produced human triggered
 avalanches on Wednesday. These avalanches likely occurred on steep
 wind-loaded slopes. Today with a forecast for more snow and wind,
 these slopes remain avalanche prone and a CONSIDERABLE avalanche
 danger exists on all wind-loaded slopes. A MODERATE danger exists
 on non wind-loaded slopes steeper than 35 degrees. Less steep non
 wind-loaded slopes have LOW danger.


 The northern Gallatin Range and northern Madison Range:

 The most recent avalanche activity in the mountains around Big Sky
 occurred on Wednesday. The avalanches were human triggered and
 fractured on faceted crystals near the ground. Uncertainly about the
 strength of this layer continues to provoke concern about avalanches
 especially on steep wind-loaded slopes. Today the avalanche danger on
 wind-loaded slopes steeper than 35 degrees remains CONSIDERABLE. A
 MODERATE avalanche danger exists on all other slopes.


 The Bridger Range:

 Yesterday ski patrollers at Bridger Bowl reported wind slabs formed on
 the lee side of ridges and gullies. Most slabs were less than a foot
 thick and didnt readily fracture with explosives or under skis.

 While avalanches in the Bridger Range arent likely, human triggered
 avalanches are possible thus a MODERATE avalanche danger exists on
 wind-loaded slopes steeper than 35 degrees. A LOW danger exists on all
 other slopes.