Archived Advisory for Tue Dec 25 2007

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CHRISTMAS DAY 2007

Merry Christmas! This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Tuesday, December 25th, at 7:30 a.m. Ron, Scott, Mark and I wish all of you a Merry Christmas and Happy Holiday! Hopefully you’ve been good little boys and girls and are ripping open your new skis or revving up your Xmas sled! As always, this advisory does not apply to operating ski areas.

MOUNTAIN WEATHER

Old Man Winter certainly was generous with the Christmas gift of snow yesterday! The northern mountains got 8-10 inches of creamy snow while the southern areas got 4-6 inches. Temperatures have dropped from the high 20s into the single digits as ridge winds calmed to 10-20 mph out of the northwest. Today will only warm a few degrees, winds should remain light and skies will be partly cloudy. By early tomorrow morning we’ll have a trace to 1 inch of new snow in the south from an approaching weather system.

SNOWPACK AND AVALANCHE DISCUSSION

The Bridger Range:

I was in the Bridger Range yesterday during the morning storm. Graupel, small ball-bearing like snow, fell out of the sky at a furious clip. Four to five inches of it accumulated before turning to snowflakes which were compacted together from the wind. We usually don’t see thick layers of graupel like this, and it could be a problem with a wind-load. It fractured easily in our stability tests and my partners and I captured it on video and in a picture.

Video: http://www.youtube.com/watch?v=GYm0xFnsiAE

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

Winds were loading some of the steeper slopes near the ridgetops yesterday, although the avalanche activity was mostly sluffs of loose snow. Wind-loaded slopes will be our primary avalanche concern, while all other slopes will provide fantastic, Christmas Day skiing. For today, on wind-loaded terrain, the avalanche danger is CONSIDERABLE if it’s steeper than 35 degrees and MODERATE on less steep. Slopes without recent wind-loading will have a LOW avalanche danger.

The northern Gallatin and northern Madison Range:

Eight to 10 inches of snow fell around Lone Peak, although the Yellowstone Club was only showing 5 inches. The Big Sky Ski Patrol reported a pulse of rain ahead of the snow which misted to the summit elevation of 11,000 feet. Quite bizarre. Moonlight Basin Patrol found the new snow to easily avalanche. West to northwest winds during the day blew this snow around where it turned the creamy powder into soft slabs. In the backcountry these areas will be your problem spots. For today, on wind-loaded terrain, the avalanche danger is CONSIDERABLE if it’s steeper than 35 degrees and MODERATE on less steep. Slopes untouched by the wind will have a MODERATE danger if it’s steeper than 35 degrees and a LOW danger everywhere else.

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

The Lionhead and Taylor Fork area of the southern Madison Range got 4 inches of new snow while the mountains outside Cooke City got 6 inches. This new, dense snow fell with westerly winds and likely created soft slabs of wind deposits near the ridgelines. Instability in the southern mountains has been persistent with collapsing and/or natural avalanche activity reported on Skyline Ridge, as well as Lionhead Peak and around the Bacon Rind drainage. This activity is due to faceted, weaker snow found both near the ground and at mid-pack. Yesterday’s snowfall, along with the recent wind loading, is preventing the avalanche danger from dropping.

For today, wind-loaded terrain has a HIGH avalanche danger if it’s steeper than 35 degrees and a CONSIDERABLE danger on less steep slopes. For slopes that are protected from the wind the avalanche danger is still rated CONSIDERABLE if they are steeper than 35 degrees and MODERATE on less steep.

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 email with your observations. You can reach us at 587-6984 or through our website www.mtavalanche.com.