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GNFAC Avalanche Advisory for Mon Apr 5, 2010

Not Current Advisory

Good Morning. This is Eric Knoff with the Gallatin National Forest Avalanche Advisory issued on Monday, April 5, at 7:30 a.m.  Montana Ale Works, in cooperation with the Friends of the Avalanche Center, sponsors today's advisory.  This advisory does not apply to operating ski areas.

Mountain Weather: 

The existing ridge of high pressure that delivered sunny skies and nice weather will remain over southwest Montana through the early part of today.  Currently, skies are mostly clear, mountain temperatures are in the mid to upper teens and winds are light out of the W-SW at 5-15 mph. 

Today, mountain temperatures will rise into the low forties and winds will gradually increase out of the W-SW.   We will begin to see increasing clouds and stronger winds later in the day as an approaching storm system moves into the area.  This storm system will deliver scattered snow showers by late this afternoon, but will intensify this evening bringing 6-8 inches of new snow to the mountains by tomorrow morning. 

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:

Winter is trying to make a comback!  This past week has been a stormy one and our snowpack is trying hard to support the added stress from the latest round of storms.  Over the past few days, strong S-SW winds have been transporting snow near ridgelines and across exposed slopes at lower elevations, creating unstable conditions on steep slopes.  These areas of wind drifted snow are now sitting over a variety of weak layers 1-3 below the surface, all of which have the ability to fail and produce avalanches.    

Yesterday, natural avalanches were observed in the in the northern and southern Madison Ranges as well as the Bridger Range, indicating weak layers in the snowpack are struggling to support the new load (photo1, photo2).  Any avalanche involving fresh wind slabs will hold the chance of stepping down into deeper layers, making for more dangerous avalanche conditions.  A skier yesterday triggered an avalanche in the southern Madison Range that initiated as a small wind slab, but stepped down to include the snow deposited in Tuesday's storm.  This slide broke 150 feet across, ran 1,000 vertical and occurred on a north facing slope.  Another skier in the northern Madison Range observed a large natural avalanche on a north facing slope that was triggered by a cornice drop and propagated close to 500 feet across.  This slide initiated as a wind slab, but pulled out deeper layers as it traveled down slope.  

Today, natural avalanche activity will be unlikely, but the possibility of triggering an avalanche still exists.  For this reason, careful snowpack evaluation, cautious route finding, and conservative decision making will be essential for safe travel in avalanche terrain.  With wind slabs sitting over weak layers, the avalanche danger is rated CONSIDERABLE on all wind loaded slopes steeper than 35 degrees.  All other slopes have a MODERATE avalanche danger.

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.

Audio: 
Audio for Apr 5, 2010