Confidence
Fair - Due to the number of field observations
Weather Forecast
Saturday: Chinook conditions expected on the east side of the divide with strong winds and temperatures up to 5 degrees between 1200m and 2500m elevation. Elsewhere, cloudy with scattered flurries are expected to bring no more than 5cm of new snow. Freezing levels expected to remain at or near valley bottoms with treeline temperatures around -2. Ridge top winds are expected to be moderate southwesterlies. Sunday and Monday: Chinook conditions are expected to persist east of the divide, while elsewhere a mix of sun and cloud with isolated light flurrries possible. Freezing levels rising as high as 1800m with strong westerly alpine winds.
Avalanche Summary
Reports from yesterday include a few thin fresh natural wind slab avalanches up to Size 1.5, and 2 Size 1.5 explosive triggered wind slabs running on older faceted snow with generally wide propagation, but slow moving.
Snowpack Summary
Light incremental snowfall is starting to bury surface hoar and a faceted upper snowpack. Snowpack depths at treeline seem to vary from 50 - 110 cm with high variability in wind-exposed areas. Buried surface hoar and facets, with an associated crust, are down approximately 30-40cm. Recent snowpack testing on this persistent weakness gave easy results and some whumpfing. The base of the snowpack is made up of weak facets and depth hoar. This deep persistent weakness may be stubborn to trigger, especially in deeper snowpack areas, but the sensitivity to triggers likely increases in shallower locations, especially on a steep, convex slopes. In some areas it is below threshold below treeline, and early season hazards like open creeks, and stumps exist.
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.