Confidence
Fair - Due to limited field observations
Weather Forecast
A strong ridge of high pressure persists through Monday bringing a mix of sun and cloud, light-moderate N-NW winds, and daytime freezing levels as high as 2500m.
Avalanche Summary
Several thin wind slabs avalanches were reported in the Coquihalla Pass area on Thursday. Although it may be harder to trigger some of the deeper weaknesses in the snowpack, if you do, the resulting avalanche could be very large and destructive.
Snowpack Summary
Strong upper level winds have created wind slabs and scoured areas in exposed terrain, primary on NE-SE aspects. There is a solid rain crust, down 15-30cm below 1800m, which has greatly reduced the likelihood of avalanches at lower elevations. A surface hoar layer has been observed down approximately 45cm in the Duffey Lake area. A facet layer near the base of the snowpack continues to give sudden collapse ("drops") results in snowpack tests. Continued caution is recommended in shallow snowpack areas (lots of rocks or small trees poking through), especially on sun exposed slopes if the sun has any kick, and on any slope that has not recently released.
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.