Archived Advisory for Sat Jan 3 2009

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SATURDAY, JANUARY 3

Good Morning, this is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Saturday, January 3 at 7:30 a.m. Bridger Bowl, in cooperation with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.

AVALANCHE WARNING

A Backcountry Avalanche Warning continues for the southern Gallatin and southern Madison Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City and the Washburn Range in northern Yellowstone National Park. In the past 24 hours another 9 inches of snow accumulated near West Yellowstone and 15 inches accumulated near Cooke City. This snow has created dangerous avalanche conditions in which natural and human triggered avalanches are very likely. The avalanche danger is HIGH on all slopes. All avalanche terrain and avalanche runout zones should be avoided.

MOUNTAIN WEATHER

Since yesterday morning, another 13-15 inches of snow fell in the mountains near Cooke City, 9 inches fell near West Yellowstone, 3-5 inches fell near Big Sky, and 2-3 inches fell in the Bridger Range. Temperatures at 4 a.m. were near 0 degrees F and westerly ridgetop winds were blowing 15-30 mph. Today will provide a break in snowfall for southwest Montana. Skies will be mostly cloudy this morning and the sun should show itself some this afternoon. Temperatures at 9000 ft will warm into the single digits F, and winds will blow 10-15 mph from the west northwest.

SNOWPACK AND AVALANCHE DISCUSSION

The southern Gallatin Range, the southern Madison Range, the mountains near West Yellowstone and the Lionhead Area, the mountains near Cooke City, and the Washburn Range:

Once again significant snow has accumulated further stressing a snowpack near its breaking point. The mountains near Cooke City have been hit especially hard with over 3 feet of new snow since mid-week. Many slopes which previously slid have been reloaded and will produce more avalanches. This situation has occurred in Yellowstone National Park near Sylvan Pass. Strong winds have produced thick wind slabs which will create deadly and destructive avalanches. These avalanches can be triggered from long distances and will slide far into their runout zones. On Tuesday, a snowmobiler parked in relatively flat terrain was buried when another rider on an adjacent slope triggered the slope above him. He was quickly rescued uninjured by his partners. In many cases, avalanches have slid on a layer of weak faceted snow sometimes near an ice layer about 1-1.5 ft above the ground. With significant amounts of new snow, avalanches will also occur on lower density snow capped by newly formed wind slabs. For today, avalanches are very likely and a HIGH avalanche danger exists on all slopes.

The northern Madison Range:

The mountains around Big Sky have not received as much snow, but snow has fallen continuously for the past 5 days. The stress from this cumulative loading and strong winds this week causes concern. Avalanches have occurred on Buck Ridge just south of Big Sky and on a small cut bank on Lone Peak. This cut bank produced an avalanche with a 1-2 ft crown, and the rider was fortunately not caught. Small slopes may not seem dangerous, but they can produce deadly avalanches. A skier was killed in Colorado in mid December on a slope less than 200 ft vertical. Natural avalanches and collapsing or cracking will not be widespread, but I expect human triggered avalanches for today on any wind loaded slope or any slope steeper than 35 degrees where the avalanche danger is CONSIDERABLE. Other slopes have a MODERATE danger.

The Bridger and northern Gallatin Ranges:

Less avalanche activity has occurred in the Bridger and northern Gallatin Ranges where less snow has fallen this week. Skiers on Mt Ellis experienced some collapsing and found a somewhat supportable snowpack. A layer of weak faceted snow about 2 ft above the ground propagated fractures in stability tests and required moderate force to fail. The Bridger Bowl Ski Patrol noted a natural avalanche on the west side of the Bridger Range on a wind loaded slope. For today, a CONSIDERABLE avalanche danger exists on all wind-loaded slopes. Non wind-loaded slopes have a MODERATE danger.

AVALANCHE EDUCATION

An Avalanche Awareness Class for Snowmobilers will offered in West Yellowstone this weekend, January 3 and 4 with a classroom session from 12-4:30 today in the Yellowstone Holiday Inn and an all-day field session tomorrow. A $30 donation to the Friends of the Avalanche Center is suggested.

A FREE 1 hour Avalanche Awareness lecture will be given at the Basecamp in Billings on Thursday, January 8 at 7:30 p.m.

Doug 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.