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Avalanche Forecast

Archived

Dec 15th, 2019–Dec 16th, 2019

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

Regions

South Columbia.

At and below treeline, 20 to 30 cm of storm snow rests on surface hoar which teeters on the brink of becoming a touchy storm slab problem.

Confidence

Moderate -

Weather Forecast

SUNDAY NIGHT: Cloudy with clear periods, light to moderate northwest wind, alpine high temperature -10 C.

MONDAY: Flurries, accumulation 5 cm, moderate west wind, alpine high temperature -9 C.

TUESDAY: Flurries, accumulation 5-10 cm, moderate west wind, alpine high temperature -6 C.

WEDNESDAY: Scattered flurries, moderate southwest wind, alpine high temperature -6 C.

Avalanche Summary

On Saturday there were two reports of skier triggered persistent slab avalanches size 1-1.5. One was on a south aspect at 2200m and was about 25-45 deep.

Reports from Thursday and Friday mostly describe sloughing and small loose dry avalanches up to size 1. Soft storm slabs propagating at ridgetops but breaking up quickly as they ran, were also limited to size 1.

Snowpack Summary

20-30 cm of new snow has covered a widespread layer of large, feathery surface hoar crystals. The new snow can be expected to gain cohesion and settle into a slab treeline and below.

A weak layer formed in late November is now buried around 1 m below the surface. This is the layer of concern relating to the listed persistent slab avalanche problem. The weak layer may present as surface hoar, a crust, facets or a combination, depending on elevation and aspect. Below this, a variety of crusts from late October are buried deeper in the snowpack.

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.