Confidence
Fair - Forecast snowfall amounts are uncertain on Sunday
Weather Forecast
Saturday: Flurries possible with light southerly winds. Freezing level around 1400 m. Sunday: Light precipitation starting late in the day, with amounts of around 5 mm expected. Freezing level around 1300m, winds light southerly. Monday: A ridge of high pressure builds brining a dry day with sunshine. Freezing level around 1200 m.
Avalanche Summary
The last avalanche reported from this region occurred on Wednesday, when a natural cornice fall occurred. This large trigger pulled out a size 3 slab avalanche from the slope below on a north aspect at 1800 m.
Snowpack Summary
Light amounts of new snow (5-10 cm) has buried an assortment of old snow surfaces comprising, depending on location, crusts, old wind slab, surface hoar and surface facets. The crusts formed on all aspects at lower elevations and on steep solar aspects higher up. Old wind slabs were on a variety of aspects behind exposed terrain features. The surface hoar (5-10mm) was most prominent at and above the recent cloud associated with inversion conditions. Surface facets have grown particularly on northern aspects where colder temperatures have persisted. In general the snowpack is now well bonded in most locations. A mid-pack layer of concern is a rain crust (buried on Feb 1st) now down 10-40 cm, which exists up to about 2000 m. This may have potential to become reactive with additional snow load in areas where additional crusts do not lie above it, such as north aspects at treeline. Lower layers include a mid-January crust (down 50-100 cm), and a mid-December crust (down up to 200 cm); these now only present concerns in shallow snowpack areas. The average snowpack depth at 1650m is around 240cm.
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.