We're dealing with an unusual snowpack right now on the Sea to Sky. Check out the recent Forecasters Blog post for a more detailed discussion
Weather Forecast
Tonight and Wednesday: An inversion will bring fog patches over the low lands and clear conditions up high. Later, a trace to light precipitation is expected with the passage of an unstable airmass with moderate to strong winds from the W shifting from the NW. Freezing levels should lower back to 1300 m. overnight and rise back up again tomorrow to 2000 m. Expect a bit of sun over the region during the day. Thursday: A ridge of high pressure is well in place. Sunny skies and continuing rising freezing levels starting at 2000 m until 3000 m on Friday. Light winds from the W. Friday overlook: Ridge is still dominating the pattern with clear skies and warm temperatures.
Avalanche Summary
Explosive control resulted in avalanche up to size 2.5 some of which ran in the upper storm snow and another in the deep persistent slab on a NE aspect slope. NorthEast of the Sea to Sky region, a significant natural avalanche cycle happened yesterday with the morning heating . Avalanches up to size 3.5 released in the depth hoar basal layer many of which were remotely triggered or naturally triggered. These mostly occurred on N and E facing slopes. Numerous natural avalanche up to size 2.5 are suspected to have released in the late November persistent weak layer.
Snowpack Summary
Past and forecasted moderate to strong winds from the SW-W and NW have formed large windslabs in the alpine and at treeline and scoured windward slopes. I suspect these are bonding rapidly with the present mild temperatures. These windslabs and the old storm snow in sheltered terrain could possibly become more reactive and create moist avalanches as freezing levels rise up tomorrow. This is especially the case for steep slopes getting hit by solar radiation. What is not healing so rapidly is the underlying deep persistent weak layers of facets around crusts and basal facets. At higher elevations, where the snowpack was deeper, the facets likely co-exist with a crust. At lower elevations, or in thin rocky alpine features, more widespread facets exist down near the ground. This makes for a low probability high consequence avalanche scenario that is more commonly associated in the interior of the province. In glaciated terrain open and poorly bridged crevasses are everywhere although now they are hiding under a meter of unsupportive storm snow.
Problems
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.
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.