Archived Advisory for Fri Jan 2 2009

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FRIDAY, JANUARY 2

Good Morning, this is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Friday, January 2 at 7:30 a.m. Yellowstone Rental in West Yellowstone, 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. Nearly continuous snowfall has kept the snowpack at its breaking point. Natural and human triggered avalanches have occurred on many slopes which have been reloaded by new snow and wind drifted snow. These slopes will produce more avalanches. With heavy snowfall predicted to occur today, the avalanche danger remains HIGH on all slopes. The snowpack is very unstable. Natural and human triggered avalanches are likely. Avalanche terrain and avalanche runout zones should be avoided.

MOUNTAIN WEATHER

During the past 24 hours, 10-12 inches of snow accumulated in the mountains around Cooke City, 5-7 inches fell near West Yellowstone, and 3-5 inches fell in the mountains around Big Sky and Bozeman. This morning at 4 a.m. temperatures were in the mid 20’s F and winds were blowing 20-40 mph from the west in the Bridger Range and south-southwest elsewhere. Today temperatures will slowly drop to near 10 degrees F by this evening. Winds will also decrease, but they will continue to blow 30 mph from the west until this afternoon when they should be 10-15 mph. Today Pacific moisture from the southwest will produce snowfall while a cold front slowly descends from the north. Snowfall will taper off this evening, but an additional 8-10 inches should accumulate near Cooke City, 5-7 inches near West Yellowstone, and 3-5 inches in the mountains around Bozeman and Big Sky.

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:

During past 2 weeks, there have been only two or three days without snowfall. In the past 48 hours, the mountains near Cooke City received over 2ft of new snow. This snowfall means the snowpack has been continually stressed and has not been given time to adjust to the loading. Additionally, much of this snowfall has been accompanied by high winds which have scoured some slopes and further loaded others. Skiers and riders have reported significant avalanche activity as well as widespread collapsing and cracking of the snowpack. You can see pictures of some of these avalanches and this cracking at:

http://www.mtavalanche.com/photos/photos.php

Many slopes, which already slid, have been reloaded by new snow and wind drifted snow. Avalanches are again likely on these slopes. Other slopes only need the added weight of a skier or rider to produce an avalanche. In most cases avalanches have occurred on faceted snow surrounding an ice layer buried 2-4 feet deep. This ice layer has decomposed in some areas and is harder to find, but the weak faceted snow remains obvious in snow pits. Snowfall will continue today, and the avalanche danger is HIGH on all slopes.

The Bridger, northern Madison and northern Gallatin Ranges:

In the mountains around Bozeman and Big Sky, strong winds have stripped snow off many slopes and formed large wind slabs on others. Avalanche activity has decreased in these mountains, yet stability tests continue to produce clean shears in both faceted snow 1-2 ft above the ground and less dense snow under recently formed wind slabs. In the backcountry and ski areas, most avalanche activity has been confined to steep wind loaded slopes where human triggered avalanches remain probable. Few slopes have been unaffected by wind as my partner and I found on Mt Blackmore on Wednesday. We felt avalanches were less likely on either scoured or non wind loaded slopes, but avalanche remain possible on these slopes. For today, a CONSIDERABLE avalanche danger exists on all wind-loaded slopes. Non wind-loaded slopes have a MODERATE danger.

PLEASE NOTE

There have been 11 avalanche fatalities in the U.S. this winter but none in Montana. Several close calls have occurred near Cooke City, and fortunately no one has been injured in an avalanche. Please continue to have fun and play it safe.

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 on Saturday in the Yellowstone Holiday Inn and a field session on Sunday. A $30 donation to the Friends of the Avalanche Center is suggested. Check the calendar on the education page of our website for more information.

I 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.