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Avalanche Forecast

Archived

Jan 7th, 2018–Jan 8th, 2018

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

Regions

Purcells.

A weak layer is buried at a depth prime to human triggering. As the overlying snow gains slab properties from new snow and warming, destructive avalanches may result. Cautious route finding is advised.

Confidence

High -

Weather Forecast

MONDAY: Cloudy with light snowfall, accumulation 2-5 cm, moderate to strong southwesterly winds, alpine temperature near -5 C, freezing level near 800 m.TUESDAY: Cloudy with light snowfall, accumulation 5-10 cm, light to moderate southwesterly winds, alpine temperature near -7 C, freezing level near valley bottom.WEDNESDAY: Partly cloudy with intermittent flurries, light to moderate southwesterly winds, alpine temperature near -14 C, freezing level below valley bottom.

Avalanche Summary

Numerous signs of instability have been noted in the snowpack over the past week, including whumpfing and cracking between 1700 and 2100 m, and two skier-triggered avalanches suspected to have released on the December 15 weak layer. Expect the potential to trigger persistent slabs to increase as the snow continues to settle into a cohesive slab.Please share your recent observations through the Mountain Information Network.

Snowpack Summary

New snow (2-15 cm across the region) has accumulated on surface hoar in sheltered slopes and a sun crust on steep solar aspects. This new snow may be deeper in northwesterly lee features due to moderate southwesterly winds at treeline and alpine elevations.A warming trend and new snow could create a dangerous slab above buried weak layers in some areas. Numerous persistent weak layers exist in the snowpack. Dry snow overlies two layers composed of weak and feathery surface hoar, with the deeper layer (December 15) buried 40 to 80 cm. This layer is found most often around and below treeline but has been reported as high as 2400 m. As the overlying dry snow becomes more cohesive and forms a slab, this layer has the potential to create easily-triggerable destructive slab avalanches. Where and when this will occur is tricky to predict and even professionals are scratching their heads about it. It is a good time for conservative decision-making.Deeper in the snowpack (70 to 110 cm), a November crust is producing variable snowpack test results, from sudden fracture characters to no result. This layer is considered dormant but could be triggered where the snowpack is thin.

Problems

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.

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.