Regions
Northwest Coastal.
Watch for wind slabs in unusual places, including low elevation terrain.
Confidence
Moderate - Wind effect is extremely variable
Weather Forecast
Kasiks (1435m):HN24 9cm; TMin -5; TMax 0; winds 30-50 NWShames (740m):6cm/6mm; TMin -5; TMax -3Bear River Ridge (1995m):Windy Upper (1490m):winds 30-60 W then NWEndgoal (370m):HN24 4cmSnowbank Mid (1065m):HN24 3cmRevision (1500m):20-35 W then NW
Avalanche Summary
Explosive control work on Tuesday and Wednesday managed to produce some large avalanches that failed on the crust buried at the end of October on north through east aspect alpine slopes in the Stewart area and north of Stewart. A natural storm avalanche cycle was observed last weekend up to size 2.5.
Snowpack Summary
The region picked up 20 to 60cm of storm snow last weekend accompanied by winds out of the southwest, west, northwest, and most recently the east. Since then, little additional snow has fallen, but cooler temperatures have kept snow dry and susceptible to being blown around by the wind. Wind slabs may rest on a melt freeze crust (reported to be 3 to 15cm thick), and there are reports there also may be surface hoar resting above this crust in sheltered locations. Below this crust the mid-pack is reported to be generally strong. You can expect to find a second prominent crust, which was buried at the end of October, 100 to 200cm below the surface. This lower layer may have associated facets, particularly in more shallow locations.
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.
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.