Watch for clues of changing conditions as there is potential for fresh wind slab formation on alpine features Friday.
Confidence
Fair - Forecast snowfall amounts are uncertain on Friday
Weather Forecast
FRIDAY: Freezing level holding at 1800m. Strong south winds at treeline, strong to extreme SW winds at ridge-top. Clear skies at dawn building to overcast by lunch. No significant precipitation expected during the day. 2 to 5mm of precipitation expected Friday night, less than 10cm total snowfall expected.SATURDAY: Freezing level hovering around 1500m. Scattered flurries, less than 5cm of snow expected. Moderate W/SW winds at treeline, strong W winds at ridge-top. Overcast.SUNDAY: Freezing level rising to 1500m. Moderate W winds at treeline, strong W/SW winds at ridge-top. Overcast skies, no significant precipitation expected.
Avalanche Summary
A few natural cornice failures were observed Wednesday, but slabs were only triggered in steep, unsupported rocky features and even then had minimal propagation. On Tuesday cornice failure triggered a size 3 avalanche on a North facing feature at 2700m.
Snowpack Summary
The current surface consists of surface facets and surface hoar. Below this is the 15-30cm of new snow that fell last weekend. This snow remains dry on high elevation polar aspects but has turned moist on east and west facing aspects. South facing features are moving into the spring corn cycle. Moist snow exists underneath this most recent storm snow in most of the region.Two significant persistent weak layers composed of crust and facets exist in the snowpack. Although they appear to have gone dormant for the time being, we will continue to monitor them closely. Mid-March is down 40 to 80cm below the surface and Mid-February is down 80 to 200cm. Down at the bottom of the snowpack a weak layer of basal facets exists. Large loads like cornice/ice fall or even sustained warming could initiate an avalanche on this very deeply buried weak layer.
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.