Thoughtful terrain selection and conservative group management are essential during this period of considerable avalanche danger.
Weather Forecast
Precipitation will ease late this afternoon but expect moist snow and rain below 2000m. Possible sunny breaks later in the day with alpine temperatures reaching zero and moderate to strong SW winds. Freezing levels drop overnight and climb again with the arrival of another frontal system on Sunday morning with an additional 10mm of snow and rain.
Snowpack Summary
5 cm of moist snow overnight. 65cm of storm snow overlies the Feb 27 layer, which is a crust on SE-W aspects, widespread surface hoar/stellars on shaded aspects. Large cornices and reactive wind slabs on lee features. Feb 10 surface hoar/ crust layer is down 100cm and is unreactive in tests. Snow is moist below 1900m. Rain this morning up to 1250m.
Avalanche Summary
A widespread natural avalanche cycle was observed in the highway corridor. Wind slab releases on polar aspects, loose solar triggered on solar aspects and one large cornice triggered avalanche that ran size 3. Several size 1.5 wind slab avalanches were observed in the backcountry. These avalanches were on a wind loaded east aspect.
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.
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.
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.