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 -12 TUESDAY: Mix of sun, cloud and isolated flurries / Light west wind / Alpine temperature -13 WEDNESDAY: Mix of sun, cloud and isolated flurries / Light southwest wind / Alpine temperature -8
Avalanche Summary
Reports through the weekend highlighted numerous natural wind and storm slab avalanches size 1.5-2.5 at treeline and in the alpine on all aspects. Additionally there were also reports of skier triggered wind and storm slab avalanches to size 1.5 as well as a remotely triggered size 1.5 persistent slab avalanche on a northwest aspect at 1300m. On Saturday there was a report of skier triggered size 1.5 persistent slab avalanche on a northeast aspect at 1500m with a 100cm fracture in the southern portion of the region.
Snowpack Summary
An additional 20-40cm of new snow fell Thursday through Saturday, bringing the storm snow total this week to 50 to 90cm. This storm snow has been redistributed into localized wind slabs. It covers old surfaces including faceted powder, a sun crust on solar aspects, and surface hoar on shady slopes. Around 70 to 110cm 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 solar aspects where it's associated with with small facets or surface hoar. There are several deeper layers that have shown signs of improving but still remain suspect as low probability to trigger yet will result as a high consequence avalanche if triggered. 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 snow. These layers may "wake-up" with strong inputs such as sustained warming, sustained snowfall, large triggers (e.g. cornice fall, smaller avalanches coming down from above); human triggering is also possible in shallow, rocky 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.