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Avalanche Forecast

Archived

Feb 27th, 2018–Feb 28th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
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

Lizard-Flathead.

Light amounts of new snow and strong winds on Tuesday night and Wednesday will continue to build slabs particularly at upper elevations. Also be wary of what's above you, cornices are touchy.

Confidence

Moderate - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

TONIGHT: Flurries. Accumulation 5-10 cm. Ridge wind moderate to strong, southwest. Temperature near -10. Freezing level lowering to valley bottom.WEDNESDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind moderate, southwest. Temperature near -4. Freezing level rising to 1000 m.THURSDAY & FRIDAY: Mostly cloudy, flurries heaviest overnight Thursday. Accumulation up to 5 cm. Ridge wind moderate, southwest easing on Friday. Temperature high near 0, low near -4. Freezing level rising to 1500 m on Thursday.

Avalanche Summary

Tuesday morning a size 2.5 natural storm slab, likely triggered by a cornice collapse, was reported on a northerly aspect in the alpine. Numerous wind slabs up to size 2 and loose dry avalanches up to size 1.5 were reported from the Lizard Range on Monday running either naturally or triggered by skiers testing small slopes. Explosives triggered widespread storm slabs up to size 1.5 and size 2 results on northerly aspects. Crown depths typically ranged from 40-80 cm.

Snowpack Summary

New wind slabs are building as approximately 40 cm of light dry snow has fallen in recent days and is being moved around by moderate to strong westerly winds. This storm snow overlies various old surfaces including old hard wind slabs, crusts, facets and spotty surface hoar (for example February 14 surface hoar is now 50 to 80 cm below the surface).Deeper in the snowpack, the widespread mid-December weak layer sits about 200 cm deep. This consists of a crust, facets or surface hoar.Near the base of the snowpack, a crust/facet layer could be awoken from a thin-spot trigger point, or with a very large load like a cornice fall.

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.