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Avalanche Forecast

Archived

Feb 18th, 2018–Feb 19th, 2018

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

Regions

Northwest Coastal.

Strong outflow winds have created very touchy wind slabs. Be cautious in terrain features where snow has accumulated, as the slabs will likely be easy to trigger.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Partly cloudy with increasing cloudiness, moderate northwesterly winds, alpine temperature -9 C, freezing level below valley bottom.TUESDAY: Mostly sunny, light to moderate northerly winds, alpine temperature near -8 C, freezing level below valley bottom.WEDNESDAY: Mostly sunny, moderate to strong northerly winds, alpine temperature near -5 C, freezing level below valley bottom.

Avalanche Summary

Many small to large (size 1 to 2) wind slabs were reported on Saturday in steep alpine and cross loaded terrain. They were reported to have released naturally and by skiers due to rapid wind loading from strong northeasterly winds. A small cornice failure was also noted.

Snowpack Summary

Strong northeast outflow winds have redistributed the 40-60 cm of snow that fell since Tuesday. The winds have produced touchy wind slabs in lee and cross-loaded features at all elevations (as observed in this post and this one). This snow sits on a wide variety of surfaces, including wind-scoured and old wind slabs at higher elevations, a sun crust on steep solar aspects, and facets and surface hoar in sheltered locations at treeline and below treeline elevations. The surface hoar and facets are found around 60 to 110 cm below the surface on all aspects up to elevations of 1400 m.A deeply buried crust/surface hoar layer from mid-January exists in sheltered areas at treeline and below treeline elevations. Thin spot triggering is the primary concern for this layer.

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.