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Avalanche Forecast

Archived

Mar 6th, 2018–Mar 7th, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

A buried weak layer is capable of producing large human-triggered avalanches. Stick to small supported terrain features and be cautious when slopes are getting hit by direct sunlight.

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

WEDNESDAY: Sunny in the morning with increasing clouds in the afternoon, light southwest wind, freezing level rising to around 1400 m.THURSDAY: Flurries increasing throughout the day with 5-10 cm of snow by the afternoon, moderate southwest wind, freezing level rising to around 1200 m.FRIDAY: Another 5-10 cm of snow with freezing level rising to around 1200 m.

Avalanche Summary

No notable avalanches were reported on Monday, but reports from the weekend highlight a touchy persistent slab problem in this region.Numerous reports of whumpfing around upper treeline elevations were reported, as well as a few large avalanches. An MCR report from the Blackcomb backcountry on Sunday describes a size 3 avalanche that was remotely triggered on a west aspect around 1900 m and presumably failed on the buried surface hoar layer (see photo and details here). A size 2 slab avalanche failed in a north-facing chute at a similar elevation and triggered additional smaller avalanches on nearby slopes. Closer to Squamish, a natural size 2 avalanche failed on a south aspect at 1750 m (see photo and details here). These avalanches highlight a persistent slab problem that exists on all aspects around treeline elevations. This type of problem tends to take a while to heal, and avalanches could remain reactive to human triggers throughout the week.

Snowpack Summary

A thin sun crust has formed on solar aspects and the surface is wind affected in most exposed terrain. Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust that is roughly 50-100 cm below the surface. This layer has produced whumpfing, sudden results in snowpack tests, and some remotely triggered avalanches. Lots of the activity has been on buried surface hoar on north aspects at upper treeline elevations. The snowpack is well settled and strong beneath this interface. Variable winds in the past month have produced cornices on many ridgelines. They will become touchier as they grow in size, as temperatures rise, and when they are subject to the strong late-winter sun on clear days.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.