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Avalanche Forecast

Archived

Mar 7th, 2013–Mar 8th, 2013

Alpine
Natural avalanches possible, human triggered probable.
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

Kootenay Boundary.

Confidence

Good

Weather Forecast

Thursday night and Friday: Precipitation associated with the upper low will ease off and give place to a light, cool and dry northerly flow. Light amounts are expected on Friday with light North winds and temperatures around -6 C in the alpine. Overcast skies starting to clear in the afternoon. Freezing levels will rise to 1400 m. tomorrow.Saturday: High pressure brings dry conditions, mainly clear skies, light NW winds and freezing level rising up to 1200 m. in the afternoon. Sunday: A frontal system approaches from the North coast Saturday night weakening as it hits the interior but could leave some light precipitation amounts, slightly cooler temperatures and winds switching from the SW.

Avalanche Summary

Some sluffing in steep terrain was reported. No other recent avalanches was reported.

Snowpack Summary

Around 18 cm (30 cm in the Western part of the region) of new snow fell on top of the recent storm snow above 2000 m., on a 1-3 cm thick melt freeze crust below 2000 m. and on a sun crust on S facing slopes.  This new snow is sluffing easily in steep terrain. Soft slabs were also formed on lee terrain from Easterly winds.  In much of the region, up to 80 cm snow overlies fairly well preserved surface hoar and sun crust. This interface is still producing sudden collapse results during snow tests.  A cornice fall or an avalanche in the storm snow could definitely trigger this deeper instability. The sun and warming temperatures tomorrow afternoon and Saturday will most likely weaken the snowpack and cornices especially on S facing slopes.A strong melt-freeze crust exists at 1700 m and below and is bridging deeper instabilities. 

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.