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Avalanche Forecast

Archived

Feb 11th, 2017–Feb 12th, 2017

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

Regions

South Coast Inland.

Human triggered avalanches remain likely on Sunday at treeline and above, especially in the Coquihalla. Use small slopes with low consequence to test the bond of the storm snow.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Seasonal temperatures and isolated flurries through the weekend. Significant alpine warming Tuesday onwards. SUNDAY: Mix of sun and cloud / Light - moderate southwesterly winds / Freezing level around 900 m. MONDAY: Sunny with cloudy periods, warming significantly with highs to +5 Celsius / Moderate southeasterly winds / Freezing level around 1500 m. TUESDAY: Mostly cloudy / High temperatures to +4 Celsius / Light-moderate southwesterly winds/ Freezing level around 2500 m.

Avalanche Summary

A widespread natural avalanche cycle (to Size 2.5) occurred on all aspects and elevations at treeline and above from Thursday into Friday. Spooky conditions with shooting cracks and whoompfing were reported in a great MIN post (see here for details) on Saturday afternoon on Nak Peak (Coquihalla area). Conservative terrain use is essential under these conditions.

Snowpack Summary

An additional 20 + cm of snow fell Friday into Saturday on the Coquihalla with moderate to strong southwest winds; meanwhile, only 4cm fell in the Duffey Lake zone. This new snow added to the 65-80 cm (lower amounts in the north) of recent storm snow. Temperatures rose on Thursday afternoon, increasing the likelihood slab avalanches with the heavier snow on top of lighter, drier snow. All this storm snow is sitting on a wide variety of old snow surfaces including stiff wind slab or wind affected snow at upper elevations, sun crust on steep southerly slopes, surface hoar and surface facets in sheltered locations. The mid-December facets down 130-160 cm still remain a concern especially in shallower snowpack areas in the Duffey, Hurley and/ or South Chilcotins. These deeper weaknesses warrant monitoring, especially through periods of rapid loading. In southern areas (Coquihalla), the lower snowpack is reportedly well settled (stronger), than it is to the north.

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.