Problem #1: Storm Snow:
Location: All aspects above treeline, slopes 25 degrees and steeper.
There is about 7-10" of new snow in this zone (above 2500ft), and winds have been moderate and variable over the last 48 hours, blowing from the NW and the SE at times. Rain line reached up to about 3500ft Friday, before falling to the valley floors during a period of heavy snow Saturday morning. Fresh storm slabs in the alpine may be 15-30cm thick, and will be poorly bonded in any areas where a surface hoar layer lurks below the new snow. Even low-angle slopes around 25 degrees may be prone to slides due to the very slick nature of the surface hoar layer. While this weak layer's distribution is sporadic, it will be very hard to map out and you should treat all slopes as suspect until proven otherwise. Human-triggereed avalanches are likely Saturday-Sunday within the new snow.
Problem #2: Wind Slab:
Location: Specific slopes in the alpine above 2,000ft, where north/NW winds the last three weeks caused wind loading on lee aspects beneath ridgelines and terrain features. Reports this week found areas of wind slab (3-12" thick) that are poorly bonded and easy to trigger. These new wind slabs are sliding on a buried surface hoar layer and/ or buried facets 10-30cm deep. Be sure to dig around in high-alpine areas to assess for yourself how well-bonded the upper snowpack is. Variability will be high, so evaluate each slope carefully. Hand pits and slopes tests will be helpful in mapping out this potential danger. In large or steep terrain, slabs as thin as a few inches can sweep you into dangerous situations.
January 8th Snow pit from the Lutak zone, at 2700ft, N aspect. Notice fresh wind slabs in top 15cm (easy triggering), and hard triggering down 35cm.
Observations this week found areas of D1-D2 thin natural windslab avalanches on specific terrain that was wind loaded or cross-loaded, between 2500-5000ft. These wind slabs were sliding on low-angle slopes as low as 25 degrees, and appeared to be sliding on a buried surface hoar layer 10-30cm deep. Distribution of these avalanches was limited to wind loaded areas that had been protected from strong N/NW winds.
Saturday's storm should start clearing up in the afternoon, bringing in a beautiful day Sunday with clearing skies and light winds, and temperatures just below freezing. The next storm is on tap for Monday night-Tuesday, and it should be another warm/wet one with snow levels up to about 3000ft.
( *star means meteorological estimate )
If you get out riding, please send in an observation!
Do a rescue practice with your partners. Always carry a beacon, shovel, and probe, and KNOW HOW TO USE THEM.
Practice good risk management, which means only expose one person at a time to slopes 30 degrees and steeper, make group communication and unanimous decision making a priority, and choose your terrain wisely: eliminating unnecessary exposure and planning out your safe zones and escape routes.
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