Persistent slabs have recently resulted in some very large avalanches and concerning burials. Conservative terrain selection remains critical.
Summary
Confidence
Moderate - Due to the number of field observations
Weather Forecast
FRIDAY: Mainly cloudy, Moderate southwesterly winds, and freezing levels in valley bottoms with alpine temperatures reaching -5 C.SATURDAY: Mainly cloudy with light rain/snow starting in the afternoon, strong to extreme southwesterly winds, and freezing levels rising as high as 2200 m.SUNDAY: Mainly Cloudy with light rain/snow, strong westerly winds and freezing levels dropping throughout the day to valley bottoms.
Avalanche Summary
Over the last 5 days there were several very concerning large persistent slab avalanches that were human triggered. At least 10 close calls were reported to us and several of these avalanches involved multiple people being buried. Four of these avalanches were in the Allen Creek riding area and one was in the Monashees near Blue River. These avalanches all released on or stepped down to the mid-December weak layer down 1-1.5 m in the snowpack. Check out the MIN posts and a great video on the Frozen Pirate Snow Services Facebook page for more details. Also reported on Tuesday were several natural slab avalanches up to Size 2 triggered by direct sun exposure on steep south facing slopesLooking forward, the recent storm snow may remain reactive to human triggering in wind loaded terrain and steep unsupported or convex features where buried surface hoar may remain reactive. Even if surface instabilities gain strength, deeper destructive persistent slab avalanches failing on the mid-December weak layer will remain a serious concern for the foreseeable future.
Snowpack Summary
50-70 cm of recent snow is settling over the previous mid-January snow surface which includes buried surface hoar in sheltered areas, and/or widespread facets. This slab is particularly touchy where where the buried surface hoar is preserved. Strong southwest winds during the storm have formed wind slabs in leeward terrain features. Isolated subsequent moderate outflow winds may have more recently resulted in reverse wind loading. Another surface hoar/facet persistent weakness that was buried mid-December, can now be found down 50 cm in shallow snowpack areas, or as much as 1.5 m in deeper snowpack areas. This layer woke up during the recent storm and has remained reactive to human triggers and smaller avalanches stepping down. This persistent weakness has recently been responsible for several large human-triggered avalanches including some with multiple burials, and this sensitivity is expected to continue for the foreseeable future.
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Avalanche Canada
