Friday, February 22, 2008

 Good morning. This is Mark Staples with the Gallatin National Forest
 Avalanche Advisory issued on Friday, February 22, at 7:30 a.m. The Big
 Sky Snowriders of Livingston, in cooperation with the Friends of the
 Avalanche Center, sponsor todays advisory. This advisory does not apply
 to operating ski areas.


 MOUNTAIN WEATHER

 Warm, dry and sunny weather will continue today, but the ridge of high
 pressure which has dominated this week will slowly depart late this
 afternoon. Temperatures today will rise to the mid 20s F and winds will
 be 10 mph from the south and southwest. Some clouds will build late
 today, especially to the south, and a trace to an inch of snow will be
 possible by tomorrow morning.


 SNOWPACK AND AVALANCHE DISCUSSION

 The Bridger Range:

 Despite warm temperatures and brilliant sunshine, the snow did not warm
 enough to cause significant wet snow avalanche concerns. The
 snowpack in the Bridger Range is generally stable, and the primary
 avalanche concern is wind slabs near ridge crests. These wind slabs
 have had plenty of time to bond with the underlying snow; however,
 reports from the northern Bridger Range indicate that it is still
 possible to fracture these wind slabs. For this reason, slopes
 steeper than 35 degrees with a wind load have a MODERATE danger and
 all other slopes have a LOW danger.


 The northern Gallatin and northern Madison Ranges:

 Yesterday, I skied in Beehive Basin just north of Big Sky. My partner
 and I were searching for areas of weak snow; consequently, we were
 looking for snow only 3-4 ft deep. Near the ground we found weak
 faceted snow which broke cleanly and propagated a fracture, but
 this layer of snow required significant force to fail. We also found a
 layer about a foot down which broke cleanly but did not cause much
 concern. On Wednesday, other skiers in Beehive Basin and Dudley Creek
 found similar results. The northern Gallatin and northern Madison
 Ranges have some of the weakest snow in the advisory area, and human
 triggered avalanches are still very possible. For today in these areas,
 a MODERATE danger exists on all slopes.


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

 The mountains around Cooke City and West Yellowstone have a deep
 snowpack in which stable conditions have been found. On Wednesday, I
 rode on Lionhead where my partner and I felt confident on most slopes,
 but we avoided high elevation, wind loaded slopes where dense wind
 slabs may have been sitting on a previously thin and weak snowpack.

 This combination produced a few avalanches early this week. Otherwise,
 we found layers of weak snow buried 1-2 feet deep that fractured
 cleanly. These layers required a great deal of force to fail and
 appeared to be gaining strength. For today, slopes steeper than 35
 degrees have a MODERATE danger, and less steep slopes have a LOW
 danger.