GNFAC Avalanche Advisory for Wed Feb 24, 2010

The Bridger Range, northern Madison and northern Gallatin Ranges, the mountains around Cooke City and the Washburn Range:

The last significant snowfall was nine days ago when it dumped over 2.5 feet of dense snow in the Bridger Range.  Avalanche activity spiked with the snowfall and last week skiers and snowmobilers triggered many slides throughout the northern mountains, some of them quite large (photos).  The stability has gotten better as the snowpack adjusted to this load.  It's becoming more difficult to trigger avalanches.  However, we know that weak layers persist and might slide with the additional weight of a person.  A thin layer of faceted snow 1.5 feet under the surface is fracturing in our stability tests. Facets at the ground are getting denser, but still break far and wide.  Eric and I saw this on Sunday near Flathead Pass when we investigated an avalanche from last week (video + photo).  Skiers in the northern Gallatin Range on Mt. Blackmore found these layers too, but noted they were not getting clean shears-a sign of improved stability.

Improved stability, which is what we're experiencing, is not the same as stable.  Weak layers in the snowpack, especially long term players like facets at the ground, have been avalanching as recently as last week.  I don't trust it.  There are still slopes you will be able to trigger.  The west side of the Bridger Range comes to mind.  We know that the snowpack structure is weak.  A skier could certainly punch a few steep lines without consequence, but it would be wrong to assume that all slopes are this way.  Dig, do stability tests and assess every slope; there's no shortcut.  As our zen observer in Cooke City wrote, "Dragons lurk; committing to lines involving the starting zones of big slide paths is a heavy decision, best meditated on a while longer."

For today, the avalanche danger is rated MODERATE on all slopes.  A moderate danger means that avalanches are still possible.

The southern Madison, southern Gallatin Ranges and the Lionhead area near West Yellowstone:

Yesterday, Mark and Karl went into the Lionhead area outside West Yellowstone.  Karl was in "research mode" and pock-marked another slope with snowpits.  They found increasing stability with the buried surface hoar layer 1.5 feet deep-it was breaking clean with 20 taps instead of in the low teens from a few weeks ago.  But these facets take a long time to heal.  Avalanche activity has been limited in the southern mountains not because the snowpack is strong, but simply because they haven't had much snow.  When it finally hammers down there, slopes will rip.  Mark and Eric rode into Teepee Basin on Thursday and found great riding on mostly stable snow.  On that same day skiers in Bacon Rind found better conditions than I did a few weeks ago when the area was collapsing and cracking with body weight.  Although these mountains haven't had much snow recently, the weak snowpack structure is still a concern.  Avalanches are still possible and today the avalanche danger is rated MODERATE on all slopes.

Mark 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.

Avalanche Education & Events

1.    Bridger Bowl

29^th Annual Pinhead Classic on Saturday, March, 6^th.  "Carnival" is this year's costume theme, so come dressed up to race, socialize and win great prizes. Registration fee is $30 but gets you all sorts of cool stuff. Check out the website http://pinheadclassic.com for details.

2. Moonlight Basin

Comprehensive avalanche awareness class - Thursday, March 4^th to Saturday, March 6^th

events@moonlight.com or 406-993-6026