Archived Advisory for Fri Dec 7 2007

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Friday, December 7

Good Morning. This is Mark Staples with the Gallatin National Forest Avalanche Advisory issued on Friday, December 7 at 7:30 a.m. The Community Food Co-Op, in cooperation with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory doesn’t apply to operating ski areas. Bridger Bowl Ski Area is not yet open for the season and backcountry conditions exist within their boundaries.

MOUNTAIN WEATHER

Snowfall looked promising in Bozeman yesterday morning, but only 2-3 inches have accumulated in our advisory area since then. Winds have been light, and today ridgetop winds will start to blow from the east at 10 mph and increase to 30 mph by this evening. An area of low pressure will deepen over our area today with more cold air keeping temperatures in the upper teens, and snowfall will be 1-2 inches.

SNOWPACK AND AVALANCHE DISCUSSION

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

The combination of significant snowfall and a very weak snowpack produced many natural and human triggered avalanches. Doug and Scott saw evidence of widespread natural avalanche activity in the Lionhead area on Tuesday and witnessed significant collapsing and cracking. View a video clip of their stability test at http://www.youtube.com/watch?v=5AILMR8KxyU

Evidence of natural avalanches has been seen on many of the peaks near Cooke City. On Scotch Bonnet Mountain north of Cooke City, a snowmobiler was partially buried and injured in a massive avalanche. He was riding near the bottom of the slope when he initiated the fracture which propagated over a mile. I am most concerned with the potential for fractures to propagate such long distances and trigger avalanches on slope angles as low as 30 degrees. We have found facets both near the ground and just under this week’s new snow capable of propagating these fractures. You can see a video clip of Doug on Scotch Bonnet at http://www.youtube.com/watch?v=zuc45gxLBc4

Faceted crystals have also contributed to many natural and human triggered avalanches in the mountains around Big Sky. The ski patrols in this area have successfully triggered large avalanches with explosives, and they have seen evidence of many natural avalanches on surrounding peaks especially near treeline. On Tuesday I witnessed an entire slope fracture and avalanche under the weight of one person standing on flat terrain near the top of the slope.

Mother Nature is loudly expressing warning signs in the form of this widespread avalanche activity and collapsing and cracking of the snowpack. Though you may not seen evidence of as many recent natural avalanches, the chances of triggering an avalanche are still highly probable on steep slopes and flat terrain connected to steep slopes. Remember, most avalanche victims trigger the avalanche in which they are caught. For today, the avalanche danger remains CONSIDERABLE on all slopes.

The Bridger Range and northern Gallatin Range:

The ski patrol at Bridger Bowl reported minor avalanche activity which occurred within the new snow during their recent explosives testing. Though the Bridger and Northern Gallatin Ranges have seen less avalanche activity, be cautious of steep wind loaded slopes which could avalanche. Also, watch for newly formed wind slabs in areas you wouldnn’t expect as the winds will blow from the east today. Today a MODERATE avalanche danger exists on all slopes.

AVALANCHE EDUCATION AND EVENTS

An Avalanche Awareness for Snowmobilers class is being held in West Yellowstone, Thursday and Friday, December 13th and 14th. Lectures on Thursday are being held at the West Yellowstone Conference Hotel from 12-5 pm with an all day field session on Friday. Call 597-6984 for more information.

Scott 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.