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Avalanche Forecast

Archived

Feb 11th, 2018–Feb 12th, 2018

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

Regions

South Coast Inland.

Winds have formed pockets of reactive wind slab on leeward and cross-loaded slopes at upper elevations. Also keep an eye on what's above or below you. Cornices are large and may become fragile with warm temperatures or sun-exposure.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Mostly sunny. Ridge wind moderate, northwest. Temperature -5. Freezing level 500 m. Alpine inversion.TUESDAY: Mostly cloudy, light flurries. Accumulation up to 5 cm. Ridge wind moderate gusting strong from the west. Temperature -5. Freezing level 500 m. WEDNESDAY: Cloudy with some lingering flurries. Ridge wind moderate, northwest. Temperature -5. Freezing level 700m.

Avalanche Summary

On Saturday, skiers triggered a size 2 wind slab on a north east aspect near 2000m in the Duffey zone. See the MIN report for more details. Friday there were isolated reports of natural cornice triggered and wind slab activity up to size 2.5, as well as evidence of an older large, natural size 3.5, in high alpine terrain in the Duffey Lake area.On Thursday, the southern part of the region reported a natural slab avalanche size 3.5 from a NE-SE aspect near 1800 m and numerous wet slabs up to size 2.5. An avalanche control mission using explosives in the northern part of the region saw wind slab results up to size 1.5, only running in the surface snow and not stepping down deeper.

Snowpack Summary

Last week's snowfall totals are highly variable. In the south, up to 40 cm of new snow fell bringing the alpine totals up to 60 cm for the storm ending last week. In the north, new snow totals are half that and rapidly decrease below 1800m. This new snow remains unconsolidated in wind-sheltered, shaded areas at upper elevations but has formed wind slabs in open areas at treeline and above, and scoured areas at ridge crests. At lower elevations travel is rugged and some are recommending ski crampons below tree line (!) Below the snow surface, 80-150 cm down in the mid pack sits the mid- January crust. It generally shows signs of bonding to the overlying snow; however, I would remain suspect of this deeper layer while the snowpack adjusts to the new load. Thinner snowpack areas may have a higher likelihood of an avalanche failing on this layer. Large, looming cornices exist, they are fragile and demand respect.

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.