Regions
South Coast Inland.
New snow and extreme winds will keep the avalanche danger elevated on Friday. In the Coquihalla area, where forecast snowfall amounts are the greatest, the avalanche danger may be HIGH.
Confidence
Moderate - Intensity of incoming weather systems is uncertain on Friday
Weather Forecast
Friday: 10-20cm of new snow / Strong to extreme westerly winds / Freezing level at 1400mSaturday: Light flurries / Light and variable winds / Freezing level at 1200mSunday: 5-10cm of new snow / Light southwest winds / Freezing level at 2300mNote: Confidence is low for forecast wind values and precipitation amounts for Saturday and Sunday.
Avalanche Summary
On Monday 2 people were buried in a size 2 slab avalanche in Marriott Basin in the Duffey Lake area. The touring party was large and all victims were rescued successfully by their partners, but all gear was lost. Not much is known about the aspect, elevation or the weak layer associated with the avalanche.On Wednesday in the Duffey area, explosives control triggered a size 2.5 and 2 size 3 persistent slab avalanches in north-facing alpine terrain. The early January crust was the culprit in all 3 of these avalanches. More alarming was a skier-triggered size 3 slab avalanche in the Birkenhead Lake area on the same day. The avalanche was triggered on a northwest facing slope at 2200m, was about 120cm deep and ran a distance of approximately 400m. Nobody was injured in the event. These avalanches demonstrate that you may be dealing with more than just the most recent storm snow in this part of the region.Looking forward, new snow and wind on Thursday is expected to promote a new round of wind slab activity in higher elevation lee terrain.
Snowpack Summary
As of Thursday morning 5-10 cm of new snow had fallen and was redistributed by light to moderate southerly winds into soft wind slabs in exposed 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 80-150cm 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 been sensitive to skier triggering in at last one recent avalanche in the north of the region (see Avalanche Activity Discussion for details).Below this crust lies another widespread crust which was buried at the beginning of January. This crust is thought to be generally gaining strength but has continued to show reactivity in the Duffey area.
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.