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Avalanche Forecast

Archived

Feb 8th, 2017–Feb 9th, 2017

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

Regions

Lizard-Flathead.

A Special Public Avalanche Warning Applies for this Region.There is uncertainty with forecast snow amounts and the freezing level Wednesday night into Thursday. Danger ratings are based off the higher end of snow estimates and a higher freezing level

Confidence

Moderate - Freezing levels are uncertain on Thursday

Weather Forecast

THURSDAY: Snow, accumulation 20-40cm / Moderate to strong southwest winds / Alpine temperature -2 with a freezing level of 1600mFRIDAY: Flurries, accumulation 5-10cm / Moderate to strong southwest wind / Alpine temperature -5 with a freezing level of 1400mSATURDAY: Cloudy with isolated flurries / Moderate west wind / Alpine temperature -9More details can be found on the Mountain Weather Forecast.

Avalanche Summary

Additional new snow, warmer temperatures and wind on Thursday are expected to give a spike in avalanche activity. Previously buried surface hoar, facets, and/or a sun crust may increase the reactivity and propagation propensity of new storm slabs.On Monday, several natural storm slab avalanches up to size 2.5 were observed. Explosives and skiers also triggered storm slab avalanches up to size 2 on Monday and Tuesday. These recent avalanches have had a typical slab thickness of 30-60 cm. On Sunday, natural and human triggered avalanches up to size 3 were observed on all aspects and elevations above around 1500m.

Snowpack Summary

Another 20-30cm of snow on Wednesday night through Thursday will add an additional load to the 60-80cm of storm snow accumulated last weekend. Strong shifting winds redistributed the previous storm's snow in exposed terrain forming touchy wind slabs. These wind slabs are now obscured by the latest round of snowfall. The combined accumulation of multiple storms' snow overlies a highly variable old surface which included wind affected surfaces, a layer of surface hoar in sheltered areas, facets, and/or a thin sun crust. Recent reports suggest a poor bond between the new snow and the old surface. The mid and lower snowpack are generally well settled and stable but isolated basal weaknesses may exist in shallow snowpack areas.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.