Although the temperature is forecast to remain cool at upper elevations, when the sun does come out it can have an immediate impact on those slopes directly facing it.
Confidence
Moderate - Timing or intensity of solar radiation is uncertain
Weather Forecast
MONDAY: Mix of sun, cloud and isolated flurries / Light to moderate west wind / Alpine temperature -10 TUESDAY: Mix of sun and cloud / Light west wind / Alpine temperature -12WEDNESDAY: Mix of sun, cloud and isolated flurries / Light southwest wind / Alpine temperature -7
Avalanche Summary
Reports from the weekend consist primarily of natural and explosive triggered wind and storm slab avalanches size 1.5 to 2.5 in the alpine and at treeline on northerly, easterly and westerly aspects. There are also reports of two size 1 remotely triggered avalanches (from a distance) on a west aspect in the alpine. On Thursday there was a report of naturally occurring size 2.5 persistent slab avalanche on northeast facing slope at 2400m. This was reported to be triggered from a falling piece of glacier ice.
Snowpack Summary
Storm snow amounts from the last week total 50-80cm (higher amounts in the south and west parts of the region). This new snow has been redistributed into wind slabs in wind-exposed terrain by primarily south, southwest and southeast wind. 70-100cm below the surface there's a layer buried mid-February that's a sun crust on solar aspects, and spotty surface hoar on sheltered slopes. This layer looks most concerning on on solar aspects where it's associated with with small facets or surface hoar above.There are several deeper layers that have shown signs of improving but still remain suspect as low probability - high consequence avalanche problems. We are talking about surface hoar layer buried back in December and January. Near the base of the snowpack is a November crust combined with loose sugary faceted snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall or smaller avalanches coming down from above); human triggering is also possible in shallow snowpack areas with convoluted terrain.
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.