GNFAC Avalanche Advisory for Wed Apr 7, 2010

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Not Current Advisory

Good Morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Wednesday, April 7, at 7:30 a.m. Jeff King at Edward Jones Investments, in cooperation with the Friends of the Avalanche Center, sponsors today's advisory. This advisory does not apply to operating ski areas. Bridger Bowl is now closed for the season and backcountry conditions exist.

Mountain Weather:

Yesterday an additional 4-6 inches of snow fell near Bridger Bowl and Big Sky. Most other areas received an additional 2-3 inches. Overnight skies cleared and temperatures dropped to 10 degrees F this morning with W winds blowing 10-30 mph at all elevations. An upper level ridge of high pressure will bring partly to mostly sunny skies today with high temperatures near 32 degrees F. Winds will blow from the W at 10-20 mph.

Wet Snow Avalanche Danger

This morning's cold temperatures and some clouds today should limit significant warming and wet snow avalanche activity. However, intense solar radiation this time of year can drastically change snow conditions in a matter of hours. With new snow and sunshine, the wet snow avalanche danger will be MODERATE this afternoon primarily on S and W facing slopes.

Snowpack and Avalanche Discussion:

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

Yesterday's storm dropped a total of 5-10 inches of snow and brought strong easterly winds which quickly shifted to the W and NW but remained strong blowing at all elevations. The Bridger Bowl Ski Patrol easily triggered many fresh wind slabs as did ski patrols on Lone Mountain where wind slabs formed well below ridgetops. Backcountry skiers in the Bridger Range also easily triggered avalanches in the new snow and wind-blown snow. A regular observer in Beehive Basin noted significant loading on popular west facing slopes from early E winds.

Winds remained strong overnight making fresh wind slabs the primary avalanche concern. However, recent avalanche activity throughout southwest Montana prior to yesterday's storm (summary in yesterday's advisory) indicates the existence of a sensitive weak layer buried 1-3 ft deep under the snow from previous storms. This weak layer has clearly demonstrated its potential to propagate fractures over long distances and produce large avalanches. In many cases this layer has been found on slopes with a northerly aspect and seems to be weaker in the southern half of the advisory area, but look for it all slopes. This season's snowpack continues to surprise many experienced backcountry skiers and riders and demands a pessimistic attitude about stability. Today the avalanche danger is rated CONSIDERABLE on all wind loaded slopes. Slopes without a wind load have a MODERATE avalanche danger.

I will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry let us know what you find. You can reach us at 587-6984 or email us at mtavalanche@gmail.com.

Last Advisory: This Sunday, April 11, we will issue the final advisory for the 2009/2010 season.

Audio:

Audio for Apr 7, 2010