Watch for continued wind slab development in exposed terrain Sunday and avoid areas of thin snow cover where triggering deep persistent slab avalanches is more likely.
Recent snow has been blown into soft wind slabs in lee features at and above treeline. Fresh wind slabs are likely to develop Sunday at upper elevations as strong west/southwest wind picks up.
As temperatures trend warmer in the alpine next week we have some concern about the deep basal facets reawakening. Deep persistent slab avalanches on these layers are most likely to be triggered from shallow snowpack areas near rocky outcroppings which could propagate to areas of deeper snow creating very large avalanches.
After a relatively stormy period the outlook is rather dry as temperatures begin to warm though the weekend.
SATURDAY NIGHT: Freezing level at valley bottom, moderate to strong west/southwest wind, trace of snow possible.
SUNDAY: Scattered cloud cover, freezing level at valley bottom, light southwest wind at lower elevations, strong west/southwest wind at ridgetop, trace of snow possible.
MONDAY: A few clouds, freezing level rising dramatically, perhaps as high as 2500 m, light southwest wind at lower elevations, strong southwest wind at ridgetop, no significant precipitation
TUESDAY: Overcast, freezing level lowering to about 1000 m, light southwest wind, 1 to 5 cm of snow possible.
On Friday wind slab avalanches to size 1 were sensitive to control work on a southeast facing ridge crest around 2000 m. Small natural avalanches were also observed on steep rolls.
Avalanche reports from Thursday were predominantly skier triggered wind slabs up to size 1.5. Our field team also reported a natural size 2 wind slab avalanche (details here) that stepped down to the deep persistent basal facets below a rock band. This is exactly the type of terrain where deep persistent slab avalanches are typically triggered.
On Monday, the combination of the warming alpine temperatures and the sun coming out will likely result in increased sensitivity to triggering in recent snow, especially in steep south facing terrain. This could be just the trigger for a resurgence in deep persistent slab avalanche activity.
Recent snow has been loaded into pockets of soft wind slab in alpine lees, and is settling in the mild alpine temperatures. At lower elevations it may remain unconsolidated. It sits over widespread wind slab in exposed areas at all elevations.
A well consolidated mid-snowpack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. There is potential for this deep persistent layer to reawaken as temperatures warm on Monday.
