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Avalanche Forecast

Archived

Apr 6th, 2017–Apr 7th, 2017

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

Regions

Northwest Coastal.

Exposed terrain has been walloped by strong winds. Watch for cornices and wind slabs at higher elevations.

Confidence

High -

Weather Forecast

FRIDAY: Cloudy with sunny periods and isolated flurries, moderate southeast wind, freezing level up to 1300 m after an overnight freeze.SATURDAY: 5-10 cm of new snow, light southeast wind, freezing level around 1300 m.SUNDAY: Cloudy with light flurries, moderate south wind, freezing level around 1200 m.

Avalanche Summary

Several natural and explosive triggered wind slabs were reported on Wednesday in north and west alpine features (up to size 2.5). Several avalanches were triggered by cornice falls earlier in the week, including one size 2.5 persistent slab avalanche on the February weak layer. A snowmobiler had a close call with a cornice fall on the weekend at South Douglas (click here for MIN report).

Snowpack Summary

Touchy wind slabs may still exist at higher elevations, as Wednesday's storm delivered 15-20 cm of snow above 1000 m with strong to extreme winds. Extensive wind affect is expected in exposed terrain. An overnight freeze will likely form a crust at lower elevations that will deteriorate with the heat of the day. A weak layer of facets and crusts is buried 100-150 cm deep. The layer has been unreactive recently, but a heavy trigger such as a cornice fall or intense warming may still be able to trigger it.

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.