A good day to stay away from avalanche terrain. Some natural avalanches are reaching the end of their run-outs, and activity is expected to increase tomorrow with the incoming storm.
Confidence
Moderate - Intensity of incoming weather systems is uncertain
Weather Forecast
A burst of wind and snow is expected overnight Monday, bringing 15 to 20cm of new snow by Tuesday morning. Winds will be strong to extreme out of the west, creating perfect conditions for further wind slab development. Tuesday is looking like a cloudy with sunny periods and isolated flurries. Strong winds will continue with alpine temperatures near -10 °C.
Avalanche Summary
A size 2.5 or 3 (extent of debris unconfirmed) occurred sometime today on Tent Ridge, on an East aspect at 2450m. This initiated down about 100cm and then stepped even deeper part way down the avalanche path. In addition a size 2.0 occurred on Little Tent Ridge on a SE aspect at 2350m. This one wasn't quite as deep but it did propagate across the entire feature. A couple of size 2.0 to 2.5 slab avalanches occurred on the Goat Range in the past 24hrs, initiating in the upper Alpine and running to 1/2 or 3/4 path.
Snowpack Summary
Strong to extreme West winds have created fresh wind slabs in all Alpine and Treeline terrain in lee and cross-loaded terrain. At Treeline and below several buried weak layers exist. These are surface hoar layers buried 30, 50 and 80cm on average. All these weak layers are producing sudden planar shears with the Dec 15th layer down 80cm being perhaps the most concerning. Recent avalanche activity has been observed to step down to this Dec 15th layer creating large avalanches.
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.