A series of pacific frontal systems impacting the coast in the coming days will elevate the avalanche danger.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Friday
Weather Forecast
THURSDAY: Flurries, accumulation 5-10cm / Moderate south wind / Alpine temperature -2 / Freezing level 1500mFRIDAY: Snow, accumulation 20-25cm / Moderate to strong south wind / Alpine temperature -1 / Freezing level 1500mSATURDAY: Flurries, accumulation 5-10cm / Moderate to strong southwest wind / Alpine temperature -4 / Freezing level 1200m
Avalanche Summary
Reports from Wednesday include explosives triggered storm slabs running to size 2, 30cm deep. On Monday a few natural cornice releases to size 2.5 were observed running to the bottom of their run outs entraining loose snow only. On Sunday, a natural cornice release triggered a size 3 slab avalanche which release down 60 cm and ran to valley bottom. On Thursday, expect newly formed wind and storm slabs to be reactive to human triggering. These slabs are expected to be particularly touchy where they overlie a melt-freeze crust.
Snowpack Summary
20-30cm of new snow at upper elevations sits on widespread melt-freeze crusts on all aspects and elevations except for high elevation north facing terrain. On all aspects below 2000 m and higher on sun exposed slopes, there may be multiple crust layers in the upper snowpack. Moderate to strong alpine wind from the south will have redistributed this new snow and formed additional wind slabs in the alpine and at tree line which may overlie a crust. Large overhanging cornices exist primarily on north aspects in the alpine.
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.
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.