Watch for shallow snowpack areas where triggering persistent slab avalanches remains possible.
Confidence
High - Due to the number and quality of field observations
Weather Forecast
MONDAY: Continued light flurries with 2-4 cm of new snow, light southwest winds, alpine temperatures around -15 C.TUESDAY: Mix of sun and cloud with isolated flurries, light west winds with moderate gusts, alpine temperatures around -15 C.WEDNESDAY: Light flurries with 4-8 cm of new snow, moderate west winds, alpine temperatures around -12 C.
Avalanche Summary
No notable avalanches were reported on Saturday. On Friday, several skier triggered size 1-1.5 slabs were reported on steep convex alpine features. Several large natural persistent slab avalanches have been reported on the western slopes of the Purcells, including a cornice triggered size 3.5 avalanche on the November crust and two size 2.5 avalanches the February 3rd surface hoar. Last week, three larger skier triggered avalanches were reported including a remotely-triggered size 3 persistent slab near Golden.
Snowpack Summary
Flurries delivered another 2-5 cm of low density snow on Saturday night, bring recent totals from the last week up to 15-40 cm. A pulse of moderate winds from a variety of directions formed fresh thin wind slabs at higher elevations. The recent snow has buried the mid-February interface, which is composed of a thick rain crust up to about 2000 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. Several deeper weak layers remain a concern including the February 3rd interface (40-80 cm deep) in the southern Purcells and the mid-January interface in the northern Purcells (about 100 cm deep). Basal facets may still be a reactive in shallow rocky start zones.
Problems
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.
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.