It's uncertain how the snowpack will respond to a warm, wet, windy storm. It's time to be extra conservative with your terrain choices.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
TUESDAY: Wet flurries with 5-15 cm of snow, strong southwest winds, freezing level around 1900 m.WEDNESDAY: Periods of snow and rain with 10-20 cm of snow above 1900 m and strong southwest winds.THURSDAY: Morning flurries then clearing in the afternoon with freezing level dropping to 1000 m, strong southwest winds.
Avalanche Summary
Natural storm slabs in the size 1.5-2.5 range have been reported in steep alpine terrain on a daily basis with the ongoing snowfall. Explosive cornice control on Sunday triggered numerous storm slabs and two deeper slabs that potentially failed on the February interface about 1 metre deep. Ski cutting produced several size 1.5-2 avalanches on wind loaded terrain features. Last Wednesday, a size 3.5 avalanche on Mt. Hosmer was a sign the deep persistent slab problem still exists as well.Expect a wide range of avalanche problems during the next few days of warm weather. Expect fresh storm and wind slabs at higher elevations, touchy cornices at ridgetops, unstable wet snow at lower elevations, and the possibility of large persistent slab avalanches on the February interface and basal facets.
Snowpack Summary
A warm wet storm will form fresh slabs at higher elevations while rain with fall below treeline. Strong winds will load lee features and continue to grow large cornices on alpine ridges. March has delivered regular storms with roughly 80-120 cm of snow sitting above crust and facet interfaces from February. Little is known about the distribution and reactivity of these interfaces. Isolated basal facets still exist in shallow snowpack areas and can produce destructive full-depth avalanches. Possible triggers for these deeper weak layers include cornice falls, rapid warming, or strong solar radiation.
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.
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
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.