Avalanche Forecast

Issued: Dec 20th, 2017 4:20PM

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

jmcbride, Avalanche Canada

Kootenay Boundary.

Recent storm snow totals now range from 40-60 cm. This new snow overlies a variety of old surfaces; including crusts and surface hoar, and has proven to be easily triggered by skiers. Conservative terrain choices are the key for a few more days.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY: Mostly cloudy, flurries. Accumulation up to 5 cm. Ridge wind moderate from the southwest. Temperature -8. Freezing level surface.FRIDAY: Mostly cloudy, flurries. Accumulation trace. Ridge wind light from the northeast. Temperature -8. Freezing level surface.SATURDAY: Mix of sun and cloud. Ridge wind light from the northwest. Temperature -12. Freezing level surface.

Avalanche Summary

On Tuesday, several natural and skier controlled storm slab avalanches to Size 1.5 were observed on a wide variety of aspects and elevations, while explosive control produced numerous storm slab avalanches to Size 2.5-3 on southeast to southwest aspects in Kootenay Pass.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 (whumpfing, shooting cracks, easy sudden results in snowpack tests) were reported near Nelson. See here for the great MIN report.

Snowpack Summary

Tuesday's storm delivered another 20-30 cm of snow to the region, accompanied by moderate to strong, easterly winds. Bringing the storm total to 40-60 cm for the Nelson area and parts further south. All this new snow has fallen on a variety of old snow surfaces (December 15th layer), 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. The December 15th layer now buried 30-50 cm has produced easy to moderate, resistant results in recent snowpack tests. Below the crust layer the lower snowpack is well settled.

Problems

Storm Slabs

Recent storm snow and wind have created widespread, soft slabs above the December 15th crust/surface hoar layer. Expect these slabs to be easily triggered by light loads such as a skier or rider.

Use conservative route selection, choose moderate angled and supported terrain with no consequence.Watch for signs of instability such as whumpfing, or cracking. Caution on open slopes and convex rolls below treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Dec 21st, 2017 2:00PM