Avalanche Forecast

Issued: Dec 19th, 2017 5:09PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is high. Known problems include Storm Slabs.

Avalanche Canada mgrist, Avalanche Canada

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.

Summary

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

An icon showing Storm Slabs
Conditions are expected to remain touchy with the new snow sitting on a weak surface hoar layer in many locations. Heavy snowfall on Tuesday into Wednesday will only make it worse.
Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.The new snow will require several days to settle and stabilize.Use conservative route selection, choose moderate angled and supported terrain with no consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 3

Valid until: Dec 20th, 2017 2:00PM

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