Forecast warm temperatures, sunny skies, and high freezing temperatures are expected to weaken windslabs and cornices in the alpine.
Confidence
Fair - Timing or intensity of solar radiation is uncertain
Weather Forecast
Mix of high cloud and clear skies overnight with moderate southwest winds and freezing levels dropping down to about 1400 metres. Some warm air (slightly below freezing) may remain at higher elevations overnight. Tuesday mostly sunny with a chance of high cloud combined with light southwest winds and freezing levels rising up to about 2300 metres. Cloudy with light – moderate precipitation on Wednesday with moderate southwest winds and freezing levels around 1900 metres. Mix of sun and cloud on Thursday with light winds and 1800 metre freezing levels.
Avalanche Summary
Several reports of windslabs up to size 1.5 on various aspects in the alpine that were 20-30 cm deep.
Snowpack Summary
Variable recent storm snow totals across the region are generally in the 5-25 cm range. The snow surface varies with elevation and aspect with respect to sun and wind exposure, and includes dry new snow, loose facetted snow, wind slabs, and sun crusts. The mid-February crust is down around 10-30 cm where it is not wind loaded or scoured. The late-Jan crust/surface hoar layer (up to 100 cm deep) and the mid-January surface hoar (80-120 cm deep) are generally dormant, and chances of triggering these weaknesses have decreased. However, triggering may be possible with a large input such as cornice fall, or an avalanche stepping down, especially on slopes that see a lot of sun.
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.
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.