Recent 5-15cm of snow and moderate winds from a variety of directions has created reactive windslabs on ridgecrests and at upper elevations. Caution with steep slopes where triggering a deeper layer could produce large avalanches. Happy holidays and enjoy the snow safely!
Wind slabs may be reactive to human triggering, especially in areas where the wind has stiffened the slab. Wind slabs may be found on all aspects at upper elevations because the wind direction has changed from southwest to southeast. Large and possibly fragile cornices may exist on alpine ridglines.
A 20-60 cm thick persistent slab sits above the early December crust. Around this crust are facets and potentially surface hoar in sheltered areas. Human-triggered avalanches have recently stepped-down to this layer producing size 2 avalanches in the last week.
Basal facets have the potential of forming large and destructive avalanches. The most likely place to trigger this layer would be on shallow and rocky slopes. Smaller avalanches may also have the potential of stepping down to this layer.
Mild weather for the forecast period with mainly cloudy skies, occasional sun breaks and continued cool temperatures as high pressure influences the region.
Friday night: Mainly clear. Alpine low temperatures near -8C and freezing levels valley bottom. Ridgetop wind light to moderate from the east.
Saturday: Mainly cloudy with sun breaks and isolated flurries. Alpine high temperatures near -8C and freezing levels valley bottom. Ridgetop wind light from the east.
Sunday: A mix of sun and clouds with isolated flurries. Alpine temperatures near -7C and freezing levels valley bottom. Ridgetop wind light to moderate from the south.
Monday: A mix of sun and clouds. Alpine temperatures near -6C and freezing levels valley bottom. Ridgetop wind light to moderate from the south.
No new reports on Thursday or Friday.
A MIN report submitted on Tuesday showed a deep release from a leeward high alpine feature. The deep persistent slab problem may be isolated, however; a high consequence exists if you find yourself involved in an avalanche of this size.
Last Sunday a human triggered slab avalanche size 2 was reported which started as a wind slab or storm slab and then stepped down to the early December persistent weak interface. The person was caught and partially buried. Reports from last Saturday continued to highlight the instability of slabs that have formed above the early December rain crust.
Please consider sharing your observations to the Mountain Information Network. Thank you to those that have already submitted this winter!
Recent winds and up to 10 cm of new snow have scoured some areas have built stiff wind slabs in others. Locations that have not been stripped by the wind likely have 30-50 cm of snow above an early-December melt-freeze crust with weak and sugary faceted grains around it. This layer has featured in several avalanche reports that can be found on the MIN. This interface is has been reactive to human triggering in the last week and produces size 2 avalanches.
A crust that was buried in early November sits near the base of the snowpack. This crust has weak facets associated with it. These facets have produced large avalanches in both the south and north of the region. This MIN report from December 22 highlights a deep release avalanche and the variable snowpack depths.
Snowpack depths vary substantially with aspect, elevation, and wind exposure.
