Avalanche Forecast

Issued: Mar 7th, 2018 3:57PM

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

shorton, Avalanche Canada

Kootenay Boundary.

Danger will increase as incoming snow and wind forms fresh slabs. Snowfall amounts for Thursday are uncertain, so be prepared to dial back your terrain selection if there's rapid loading.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

THURSDAY: Flurries increasing throughout the day with 10-20 cm of snow possible by the afternoon, strong southwest wind, freezing level rising to around 1500 m.FRIDAY: Flurries continue over Thursday night and into Friday and bring another 10-20 cm of snow, clearing in the afternoon, strong southwest wind easing throughout the day, freezing level rising to around 1200 m.SATURDAY: Sunny, light wind, freezing level rising to around 1500 m.

Avalanche Summary

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. No other notable activity was reported.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

Up to 20 cm of new snow could accumulate by Thursday afternoon, with even deeper deposits possible at higher elevations. The new snow is falling on mostly unconsolidated snow from last week's storm and possibly on a sun crust on south-facing slopes.A mix of interfaces 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

Storm Slabs

Fresh storm slabs will form as snow accumulates on Thursday and Friday. They will be most reactive at higher elevations and in lee terrain.

Minimize exposure during periods of heavy loading from new snow and wind.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.Be cautious of sluffing in steep terrain.

Aspects: All aspects.

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.

Be cautious on convex rolls at and below treeline where buried surface hoar may be preserved.Avoid convexities or areas with a thin or variable snowpack.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Mar 8th, 2018 2:00PM