Avalanche danger may spike on slopes receiving direct sun. Avoid travelling on or underneath sun-baked terrain.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Saturday-Monday: Mainly sunny with a few clouds and light winds. Alpine temperatures near -5, dropping overnight.
Avalanche Summary
On Thursday, wind slabs were triggered naturally and by skiers in the size 1.5-2 range, mainly on NE aspects at treeline and above. Skiers also triggered small storm slabs which failed on a buried crust. On Wednesday, a widespread natural cycle was observed, with avalanches to size 2.5 failing with solar warming. Cornice fall was also occurring.
Snowpack Summary
The snowpack is variable across the region. Recent storm snow has been redistributed by mainly SW winds into wind slabs over various crust layers in the upper snowpack. In some areas, a melt-freeze crust down about 35 cm has a questionable bond with the snow above. Surface hoar, buried down about 50-70 cm, gave hard, sudden (pops) results in recent snowpack tests. Triggering this layer has become less likely, but still remains possible with a heavy load or from a thin-spot trigger point. Cornices are large and unstable in some areas. Warm temperatures may weaken them further.
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.