Avalanche Forecast

Issued: Dec 22nd, 2017 4:45PM

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

jmcbride, Avalanche Canada

Kootenay Boundary.

The recent storm snow overlies a variety of old surfaces; including crusts and surface hoar, and has proven to be easily triggered by light loads such as a skier or rider. Check out the Forecasters' Blog here for some great advice!

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SATURDAY: Mostly sunny. Ridge wind moderate from the northwest. Temperature -11. Freezing level surface.SUNDAY: Mix of sun and cloud. Ridge wind light from the southwest. Temperature -12. Freezing level surface.MONDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light from the northwest. Temperature -12. Freezing level surface.

Avalanche Summary

On Thursday ski cutting produced small releases up to size 1 failing within the storm snow. On Wednesday numerous Size 1-2 skier, remote, and explosives triggered slab avalanches on primarily north to west aspects between 1800-2100m, failing both within the storm snow and on the December 15th crust/surface hoar layer; including a size 1.5 skier accidental.Earlier in the week numerous natural and skier controlled storm slab avalanches to Size 2 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.Also several classic signs of instability (whumpfing, shooting cracks, easy sudden results in snowpack tests) continue to be reported since Monday. See here, here and here for great MIN reports and video.

Snowpack Summary

Storm snow totals since Sunday average between 40-80 cm across the region, with the highest amounts in the Nelson area. This new snow has fallen on the "Decemebr 15th crust/surface hoar layer", 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. Recent snowpack tests have produced very easy to hard, sudden and resistant results on the December 15th crust/surface hoar layer, indicating a high degree of variability and uncertainty in this layer. Below the December 15th layer, the late November crust is now buried 70-100 cm. Beneath this crust the lower snowpack is well settled..

Problems

Storm Slabs

Recent storm snow has created soft slabs above the December 15th crust/surface hoar layer. Expect these slabs to be easily triggered especially on steep or convex terrain, and sheltered areas below treeline where buried surface hoar may exist.

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

Possible - Likely

Expected Size

1 - 3

Wind Slabs

Winds are redistributing the recent storm snow building fresh wind slabs on leeward slopes in the alpine and exposed treeline areas.

Use caution in lee areas. Recent wind loading has created soft wind slabs.

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 23rd, 2017 2:00PM