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Avalanche Forecast

Archived

Dec 20th, 2015–Dec 21st, 2015

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

Regions

Little Yoho.

Windslabs continue to develop in the alpine. Concern remains for the Dec 3rd persistent weak layer, dig frequently to check for presence of this spotty surface hoar problem and keep a watchful eye on the character of the slab above it. TH

Weather Forecast

Westerly flow will bring light amounts of precip under mainly cloudy skies with light to moderate alpine winds over the forecast period. Expect 10cm total through Wenesday. Temps will drop a bit from highs near -10 to as low as -25 at treeline overnight Monday corresponding with some clearing and diminished winds that evening.

Snowpack Summary

10 cm of recent snow has added to the faceted slab over the Dec 3 Surface Hoar now 30 to 50cm deep. While significant shears persist on this layer in isolated, shaded and sheltered areas from 1500 to 1800m, the slab above it continues to lose strength. Meanwhile moderate SW winds are steady building slabs behind prominent features in the alpine

Avalanche Summary

Reports citing windslabs up to size 2 in the alpine sensitive to skier traffic have come in over the last 24 hrs as well as a few natural cornice events. Small loose dry activity has also been seen at treeline and above, while these are of minimal consequence at this time in all but extreme terrain, their size is likely to increase.

Confidence

Due to the number of field observations

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.