There is potential for deep persistent weak layers to become active as temperatures rise in the alpine this weekend. Avoid windslabs, rocky outcroppings and areas of thin snow cover where triggering these deep avalanches is most likely.
Recent snow has been blown into soft windslabs in lee features at alpine and treeline. Keep avoiding thin or variable snowpack areas where a smaller wind slab could trigger a release on our weak basal snowpack.
As temperatures trend warmer in the alpine over the next few days, the deep basal facets may reawaken. Deep persistent slab avalanches on these layers are most likely to be triggered from shallow snowpack areas near rocky outcroppings, and propagate to areas of deeper snow.
Friday night: Mostly clear. Moderate west winds. Alpine low around -16.
Saturday: Increasing cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds, becoming strong at ridgetop. Alpine high around -8.
Sunday: Mix of sun and cloud. Moderate southwest winds, strong at ridgetop. Alpine high around -3.
Monday: Mix of sun and cloud. Moderate southwest winds, strong at ridgetop. Alpine high around 0.
Avalanche reports from Thursday were predominantly skier triggered windslabs up to size 1.5. Our field team also reported a natural size 2 windslab avalanche 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 and may be a preview of what is to come over the weekend...
On Sunday, 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 windslab in alpine lees, and is settling in the mild alpine temperatures. At lower, colder, calmer elevations it may remain unconsolidated. It sits over widespread windslab 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 in the warm alpine temperatures later in the weekend.
