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Avalanche Forecast

Archived

Dec 9th, 2019–Dec 10th, 2019

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

Regions

South Columbia.

Avalanche activity related to last week's storm has slowed down but several buried weak layers remain active. Use caution when pushing out into more complex terrain.

Confidence

Moderate - Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

Monday Night: Scattered cloud, alpine low -10, moderate northwest wind.

Tuesday: Cloudy with sunny periods and isolated flurries, alpine high -4, moderate southwest wind.

Wednesday: Cloudy with flurries, alpine high -4, moderate southwest wind increasing to strong overnight.

Thursday: Periods of snow accumulating 5-10 cm, alpine high -4, strong southwest wind easing to moderate.

Avalanche Summary

Natural storm slab activity has slowed down since the end of the storm. Explosive control work producing avalanches up to size 3 have been reported along the Highway 1 corridor. Within the last week, there have been a few reports of persistent slab avalanches failing on a layer of surface hoar (down 60-100 cm) at treeline elevations.

Snowpack Summary

20-40 cm of new snow from the latter part of last week has covered a layer of feathery surface hoar that has been found at all elevations. A thick layer of faceted crystals, previously wind-affected surfaces, and/or surface hoar in sheltered areas (around treeline and below) is now 40-80 cm below the surface.

An additional layer of surface hoar may be found in sheltered areas around treeline down 60-100 cm. In some areas this may sitting on a thin crust. A variety of crusts from late October are buried deeper in the snowpack.

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.

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.