Merry Christmas! We might be in for a series of big storms. If and when they hit, avalanche danger will rise rapidly.
Weather Forecast
A series of Pacific frontal systems will pass through the region over the next 3 days, with the heaviest snowfall amounts likely north of the highway. Strong westerly winds will intensify loading rates. Expect mild temps, with the possibility of an above freezing layer from 1500m to 2500m developing overnight.
Snowpack Summary
Up to 80cm of settled snow overlies the Dec 8 PWL, which is surface hoar at lower elevations and facets and variable wind slabs at higher elevations. This layer is becoming less reactive in tests. The lower snowpack is facetted, with 2 PWL's in the lower 50cm, that are slowly gaining strength. SW winds have formed windslabs above treeline.
Avalanche Summary
Natural slab avalanches continued occurring yesterday, even after it stopped snowing, triggered by ongoing wind-loading. They occurred from all aspects on both sides of Rogers Pass, from elevations from 2700m to 1800m, and were size 2-2.5. Several ran into the avalanche paths, moving fast and picking up mass at lower elevations.
Confidence
Intensity of incoming weather systems is uncertain
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.
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.