Alpine winds are expected to be strong NW starting Sunday increasing the danger especially with 20cm or more surface snow available for transport. Watch for slab conditions building and reverse loading patterns possibly into treeline locations.
Weather Forecast
Needle like surface hoar development is occurring from last 48 hrs weather. Sunday will be cold -10 to -20, likely strong NW alpine winds developing mid-day but remaining light at treeline elevations until Sunday evening. Snow will be light flurries the next few days and slight warming trend Monday to Tuesday.
Snowpack Summary
Light and variable winds continue to have little influence on recent 10-20cm storm snow. Snowpit at Parkers Slabs was 190cm thick, a well settled midpack, and no basal facets. Surface snow remains available for wind transport. That wind may arrive starting Sunday during the day causing the danger rating to increase as a result on Sunday or Monday.
Avalanche Summary
Good visibility today. Three size 2-2.5 avalanches were noted 24-48 hrs old, 40 degree plus, NW aspect, cross loaded gullys. Explosive work on parkers slabs on Thursday with 22 avalauncher rounds produced one size 2 slab avalanche in a windloaded location on smooth steep rock slab. Settlement and localized winds are creating pockets of slabs. �
Confidence
Wind effect is extremely variable on Sunday
Problems
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.