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Avalanche Forecast

Archived

Jan 6th, 2018–Jan 7th, 2018

Alpine
Natural avalanches unlikely, human triggered possible.
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 possible, human triggered probable.

Regions

North Columbia.

New snow is falling on numerous weak layers. As the snow gains slab properties, natural and human-triggered avalanches will become more likely. Assess the upper snowpack to observe for these slab properties. Cautious route finding is advised.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

SUNDAY: Cloudy with light snowfall, accumulation 5-15 cm, moderate southwesterly winds increasing over the day, alpine temperature near -7 C, freezing level near 800 m.MONDAY: Cloudy with light snowfall, accumulation 5-10 cm, light to moderate southwesterly winds, alpine temperature near -5 C, freezing level near valley bottom.TUESDAY: Cloudy with light snowfall, accumulation 10-20 cm, light to moderate southwesterly winds, alpine temperature near -6 C, freezing level near valley bottom.

Avalanche Summary

Recent natural, skier-triggered, snowmobile-triggered, and skier-remoted avalanches have been reported on the December 15 layer at and below treeline on all aspects.  The avalanches were generally small, being reported between size 1 and 2.  Numerous reports of whumphing were also noted in low elevation cutblocks and flat terrain.Sluffing was also noted within the new snow in steep terrain.  Reactivity of the storm and persistent slabs are likely to increase as the upper snowpack forms slab properties.

Snowpack Summary

10-15 cm of new snow fell on surface hoar in sheltered slopes and a sun crust on steep solar aspects and may not bond well to them.  The snow also may have fallen with moderate southwesterly winds in the alpine, which could have produced small wind slabs in lee features.The additional snow could create a dangerous slab above buried weak layers.  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.  As the overlying dry snow becomes more cohesive and forms a slab, this layer has the potential to create easily-triggerable destructive slab avalanches.  Snowpack tests are showing that this layer could form avalanches (i.e. sudden fracture characters, high propagation potential, whumpfing, rutschblock 1 to 3).  Deeper in the snowpack (90 to 150 cm), a November crust is producing variable test results, from sudden to no result.  This layer is considered dormant but could be triggered where the snowpack is thin.Please share your recent observations through the Mountain Information Network.

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.