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Avalanche Forecast

Archived

Mar 11th, 2017–Mar 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 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.

Regions

Purcells.

Snow, wind and warming will keep storm slabs touchy. Add the prospect of cornice triggers and the likelihood of large persistent slabs is expected to increase.

Confidence

Moderate - Freezing levels are uncertain

Weather Forecast

We'll have light snowfall amounts through to Monday morning, and then it starts to warm up Monday afternoon.SUNDAY: Cloudy with another 5-10cm of fresh snow by morning and continued light flurries throughout the day accompanied by light to moderate SW winds. Alpine temperatures hovering around -5 C.MONDAY: Cloudy with another 5-10cm by morning accompanied by moderate SW winds and freezing levels rising as high as 1800m.TUESDAY: Scattered flurries (3-5cm) with moderate southerly winds. Freezing levels remain near 1900m.

Avalanche Summary

Reports from Thursday include two 50-150cm thick Size 2-2.5 skier remote triggered deep persistent slab avalanches, failing on facets and depth hoar above the November crust with impressive propagation across an alpine wind loaded feature. See here for this informative MIN post.Subsequent explosives control produced another 40-200cm thick Size 2.5 deep persistent slab avalanche with 5m deep deposit. Elsewhere, skiers remotely triggered a 50cm thick Size 3 wind slab avalanche and extensive explosives control produced slab avalanches up to Size 3 with large full depth full path avalanches in thin snowpack areas.

Snowpack Summary

Around 20-30cm of fresh snow in the past two days has added to the 40-80cm of settled recent storm snow. Southerly winds have formed touchy slabs at upper elevations with multiple weaknesses within and under this recent storm snow.All this snow is bonding poorly to weak faceted snow and small surface hoar on sheltered shady slopes, and/or a thin crust on southerly aspects. The persistent weakness buried mid-February is lurking down 70-120 cm and composed of a thick rain crust as high as about 2000 m, sun crusts on steep southerly aspects, and spotty surface hoar on shaded aspects. This layer has produced easy results in recent snowpack tests and has proven especially reactive on steep southerly aspects. Several deeper persistent weaknesses also remain a concern, including surface hoar buried early-February (around a metre deep), and mid-January (well over a metre deep primarily in the northern Purcells). The november crust and basal facets are still sensitive in shallow, rocky start zones.

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.