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 east and then back to west. Large and possibly fragile cornices may exist on alpine ridglines.
A 30-70 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. This bond is gaining strength, but may still be reactive in steep, convex or unsupported terrain or in a step-down avalanche.
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 cool weather for the forecast period with mainly cloudy skies & isolated flurries for Sunday then a mix of sun and clouds as high pressure builds across the region for Monday / Tuesday.
Saturday night: Mainly cloudy with isolated flurries. Alpine low temperatures near -8C and freezing levels valley bottom. Ridgetop wind light to moderate from the southeast switching to southwest.
Sunday: Mainly cloudy with isolated flurries. Alpine high temperatures near -6C and freezing levels valley bottom. Ridgetop wind increasing moderate to strong from the southwest.
Monday: A mix of sun and clouds. Alpine temperatures near -6C and freezing levels valley bottom. Ridgetop wind decreasing to light to moderate from the west. A mild temperature inversion will lead to valley fog with clear warmer temperatures above.
Tuesday: Mainly cloudy with scattered flurries. Alpine low temperatures near -10C and freezing levels valley bottom. Ridgetop wind light to moderate from the southeast. A mild temperature inversion will lead to valley fog with clear warmer temperatures above.
No new reports from recent days.
A MIN report submitted on Tuesday showed a deep release from a leeward high alpine feature off the north side of Hudson Mountain. The deep persistent slab problem may be isolated, however it is very high consequence if you find yourself involved in an avalanche of this size.
Last Sunday a human triggered slab avalanche size 2 was reported near Little Simpson. It appears to have started as a wind slab or storm slab and then stepped down to the early December persistent weak interface. Reports from Dec 19th and Dec 17th continue to highlight the instability of slabs that have formed above the early December rain crust.
Recent moderate to strong winds and recent snow earlier this week have scoured some areas and have built stiff wind slabs in others. Wind directions have been predominately from the south and east souring south and east aspects and loading lee north and wast aspects. As winds shift back to the west be on the look out for buried windslabs, cross loading or reverse loading patterns.
While much of the region received 5-15cm in the recent storms, some of the higher more mountains areas may have received up to 30cm. In wind sheltered locations, there is now about 30-70 cm of snow above an early-December melt-freeze crust with weak and sugary faceted grains around it. This layer bay be deeper in deeper snowpack or wind-loaded areas - as reported from Hankin. This early December crust layer has featured in several avalanche reports from Dec 19th and Dec 17th in Hankin. This interface was reactive to human triggering in the last week and produced 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.
