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GNFAC Avalanche Advisory for Sat Apr 10, 2010

Not Current Advisory

Good Morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Saturday, April 10, at 7:30 a.m.  Team Bozeman and Yamaha, 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 was dry, with temperatures dropping last night into the mid to low teens.  Winds have calmed to 15-25 mph out of the southwest and will drop even further this morning.  Today will be sunny with light winds and mountain temperatures reaching the high 40s.  Later this afternoon clouds will increase as Pacific moisture streams in from the southwest, but not drop any measurable precipitation.

Snowpack and Avalanche Discussion: 

Wet Snow Avalanche Danger

Today begins quite chilly, but will warm rapidly. Unimpeded sunshine and light winds will allow solar radiation to quickly warm the snow surface.  I expect the wet snow avalanche danger to climb throughout the day.  Loose, wet, point release slides are the main concern.  These could easily knock you down and surf you off a cliff.  Avalanches that start out as small wet dribbles could trigger bigger slides breaking into deeper layers.  The wet snow avalanche danger on sun exposed slopes will rise to CONSIDERABLE by early afternoon. 

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

Thursday's 2-4 inch snowfall was blown to Kingdom come.  Wind speeds were clocked at 96 mph at the Yellowstone Club.  A rooster tail on Lone Peak (picture) and Mark and Eric's backcountry ski into Beehive Basin with freight train winds (video) provided clear evidence that snow was moving faster than the legal speed limit. It's easy to think that we would not see wind drifts forming since every flake of snow is on the fast track to the next county, but you'd be wrong.  Yesterday the Moonlight Basin Ski Patrol saw widespread natural avalanche activity on Cedar and Fan Mountains from this wind event.  Many of the slides broke deep with several releasing at the ground. 

Throughout our advisory area we have a weak layer buried 1-3 feet under the surface. Last week this was breaking naturally, and with human triggers, on many aspects.  Thursday's snowfall and winds have not helped the situation.  As the avalanches on Cedar and Fan Mountain demonstrated, weak snow at the ground can still fracture bringing down the entire winter's snowpack.  If you've made it this far in the season without an avalanche incident, don't start tempting the avalanche dragon now.  I haven't trusted the snowpack all season, and I'm not about to start.  Be skeptical, do stability tests and heed warnings like recent avalanche activity.

For today, all wind-loaded slopes steeper than 35 degrees have a CONSIDERABLE avalanche danger.  All other slopes have a MODERATE danger.            

Eric will issue the season's last 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.

Video: 
Strong Winds in Beehive Basin - Northern Madison Range
Audio: 
Audio for Apr 10, 2010