Expect avalanche danger to rise during the day, particularly on sun-exposed slopes. Plan to start your day early and move away from large sun-drenched slopes during the heat of the day.
Weather Forecast
WEATHER SUMMARY: It will be a sunny and warm week! Temperatures will steadily climb each day with the freezing level reaching at least 2400 m by Thursday (treeline temps near +4). Ridge winds should be generally light from the NW-NE.
Avalanche Summary
No new slab avalanches were reported on Saturday or Sunday. On Friday there were reports of skier-controlled avalanches up to size 1.5 from steep wind-loaded alpine terrain. There were also a few size 2-3 natural cornice releases. On Thursday, we had reports of storm slab avalanches up to size 2.5 in steep unskiable terrain.
Snowpack Summary
Up to 15 cm of new snow fell on Sunday, which was probably quickly affected by the sun on solar aspects (melt-freeze cycle), and northerly winds in exposed alpine terrain. There are several thin crusts in the upper snowpack on all but shaded north aspects. Approximately 30-50 cm of settled storm snow sits on a melt-freeze crust buried on Mar. 20. The late February persistent weak layer continues to be a concern for wide propagations in isolated terrain, however it may take a large trigger like a cornice fall to initiate an avalanche. Watch for recent storm snow releasing as loose wet avalanches on steep solar aspects with strong solar radiation and daytime warming this week.
Problems
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.