Avalanche Forecast

Issued: Mar 8th, 2018 4:15PM

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

mbender, Avalanche Canada

Kootenay Boundary.

Forecast snowfall amounts are uncertain Thursday night into Friday. If accumulations are higher than forecast, the avalanche danger may be higher than indicated.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

FRIDAY: Overnight Thursday into Friday snow, accumulation 15-25cm then mostly cloudy with isolated flurries through Friday / Moderate to strong southwest wind / Alpine temperature -4 / Freezing level 1000m SATURDAY: Mix of sun and cloud / light south wind / Alpine temperature -3 / Freezing level 1400m SUNDAY: Cloudy with flurries / Light southwest wind / Alpine temperature 0 / Freezing level 1800m

Avalanche Summary

Expect to see an increase in storm slab, wind slab and loose dry avalanche activity as new snow accumulates Thursday into Friday. On Wednesday reports indicated loose wet avalanches size 1.5-2 from southerly facing terrain at tree line. On Tuesday, a size 1 wind slab was skier-triggered on a south aspect at 2200 m and nearby explosive control produced a size 2 wind slab. The most recent report of a persistent slab avalanche was on Sunday, when a skier accidentally triggered a large avalanche on a north treeline slope in the Rossland area (see details here). The avalanche failed on a surface hoar layer 80 cm below the surface. Looking ahead, persistent weak layers could be stressed by the weight of the new snow or by the warming that will follow the storm.

Snowpack Summary

15-25cm of new snow is forecast to fall Thursday into Friday morning. This new snow sits on mostly unconsolidated snow from last week and possibly on a sun crust on south-facing slopes.A mix of weak layers exist 50-100 cm below the surface, including small surface hoar on polar aspects and a crust on solar aspects. These layers have consistently been reactive in snowpack tests, suggesting they could potentially remain reactive to human triggers as well. Deeper weak layers that formed in January and December have gained strength and gone dormant at this time. They include several surface hoar and facet layers 1 to 2 m below the surface and a crust/ facet interface near the base of the snowpack.

Problems

Wind Slabs

Fresh storm and wind slabs will form as new snowfall combines with moderate to strong southwesterly wind Thursday night into Friday.

Be cautious of sluffing in steep terrain.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Persistent Slabs

Weak layers exist 50-100 cm below the surface, including surface hoar on north-facing terrain and sun crusts on south-facing terrain. These layers may become reactive with the weight of new snow and warming.

Avoid convexities or areas with a thin or variable snowpack.Be cautious on convex rolls at and below treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Mar 9th, 2018 2:00PM