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Avalanche Forecast

Archived

Dec 19th, 2017–Dec 20th, 2017

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

Regions

Kootenay Boundary.

A major storm will bring impressive snow totals to the Kootenay region. It's best to avoid all avalanche terrain until the snowpack has time to settle out.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

After Tuesday's storm it will clear up and we'll have dry weather with cool temperatures for the foreseeable future.WEDNESDAY: Snow ending in the morning. Ridge wind moderate northerly. Freezing level at the surface, alpine high temperatures of -5.THURSDAY: Clouds and isolated flurries. Ridge wind moderate from the north west. Temperature near -6. Freezing level at the surface. FRIDAY: Cloudy with isolated flurries. Ridge wind moderate from the north east. Temperature near -6. Freezing level at the surface.

Avalanche Summary

On Tuesday, ski cutting produced several storm slab avalanches to Size 1.5 on a wide variety of aspects and elevations. On Monday, numerous storm slabs up to Size 2 were reported in the Nelson area: They were either easily triggered by skiers or ran naturally. Also on Monday, several classic signs of instability (whumphing, shooting cracks, easy sudden results in snowpack tests) were reported near Nelson. See here for the great MIN report.

Snowpack Summary

The Nelson area and points farther south have now seen 40-60 cm of new snow since Sunday night, with moderate to strong winds. Deep snow drifts have been reported and we also received word that the upper snow pack is 'upside down' (heavier, denser snow on top of lighter snow).All this new snow has fallen on a variety of old snow surfaces, depending on aspect and elevation. On solar aspects a thin melt-freeze crust has been buried. On northerly aspects, feathery, surface hoar crystals (10-60 mm in length) have been buried below treeline as well as protected areas at treeline. In the alpine the old surface consisted of sugary snow (facets) and hard, wind scoured snow. Below the crust layer the lower snowpack is moist and well settled.

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.