Warming and sunshine will drive avalanche danger this week. Plan to start your day early and to avoid large sun-drenched slopes during the heat of the day.
Weather Forecast
MONDAY: Cloudy with a chance of flurries early, then sunny breaks. The freezing level climbs to 1600-1800 m and winds are moderate from the N-NE. TUESDAY: Becoming sunny. The freezing level is around 1800-2000 m and winds are light to moderate from the North. WEDNESDAY: Mainly sunny. The freezing level spikes above 2200 m. Ridge winds are generally light to moderate from the North.
Avalanche Summary
No new slab avalanches were reported on Saturday. On Friday there were numerous 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 isolated steep unskiable terrain.
Snowpack Summary
Light new snow covers a melt-freeze crust on solar aspects and all aspects below treeline, dry snow on sheltered shady slopes, and wind affected snow in higher exposed 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 during periods of strong solar radiation and/or daytime warming.
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.