Snow totals are very uncertain in this weather pattern. Danger ratings are based on the higher forecast amounts of snow. New snow may add to wind slabs caused by extreme winds from Friday.
Confidence
Moderate - Forecast snowfall amounts are uncertain on Sunday
Weather Forecast
Saturday: Snow (5 - 20cm possible) / Light to moderate westerly winds / Freezing level 1800m dropping to 1000m in the afternoon. Sunday: 5-25cm of new snow / Moderate southwest winds / Freezing level at 1500mMonday: Isolated flurries / Light north westerly winds / Freezing level at 1400mNote: Confidence is low for forecast wind values and precipitation amounts on Saturday and Sunday.
Avalanche Summary
On Friday ski cutting produced several size 1 soft slabs on immediate down wind (lee) features. Explosives control on Thursday and Friday triggered cornices at ridge crests, mostly Size 1.5 - 2. Looking forward, light amounts snow and strong winds on Friday are expected to promote a new round of wind slab activity in higher elevation lee terrain.
Snowpack Summary
On Friday morning only 3-5cm of new snow had fallen overnight as temperatures warmed up to +1 at tree line. Winds, however, were strong to extreme from the south (gusting to 121 Km/hr at the peak of Whistler) and created fresh wind slabs in exposed downwind (lee) terrain. At lower treeline and below, generally light amounts of snow now overlie a melt-freeze crust which formed during last Monday's warm storm. The new snow adds to the 170cm of snow that fell during the last few weeks of January. These series of storms were accompanied by strong to extreme winds which resulted in extensive scouring and impressive cornice growth in upper elevation terrain. These accumulations sit on a crust from mid-January which generally shows signs of bonding to the overlying snow; however, it has the potential to "wake-up" with a large trigger such as a cornice fall.Below this, the snowpack is thought to be generally strong and well-settled.
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.