Avalanche Forecast

Issued: Mar 4th, 2018 3:34PM

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.

Several days of snow and wind has formed fresh slabs that could remain sensitive to human triggering throughout the week.

Summary

Confidence

Moderate - Wind speed and direction is uncertain on Monday

Weather Forecast

MONDAY: Mostly cloudy with isolated flurries and a trace of new snow, light west wind, freezing level rising to around 900 m.TUESDAY: Clearing throughout the day, light wind, freezing level rising to around 1000 m.WEDNESDAY: Sunny, moderate southwest wind, freezing level rising to around 1500 m.

Avalanche Summary

On Saturday, explosive control produced several size 1-2 storm slabs in the top 15-30 cm of snow. Widespread sluffing in steep terrain was also reported.Storm slab avalanches to size 1 were sensitive to human triggering on Friday on north and south facing terrain between 2000 and 2150 m. Control work on Friday produced storm slab avalanches to size 2.5 on southeast through southwest facing features between 1700 and 2050 m. A natural size 1.5 wind slab was reported from a steep northwest facing terrain feature at 2100 m which was likely formed by Thursday night's wind event.

Snowpack Summary

10 to 20 cm of new snow fell Friday night, bringing weekly storm totals up to 40-60 cm. Moderate to strong east/southeast winds picked up Thursday night and added some stiffness to storm slabs at all elevations. The February 23rd weak layer is now down 40 to 90 cm and is composed of small surface hoar on polar aspects and a thin crust on solar aspects. Moderate resistant planar shears were reported at this interface Friday.The mid-February weak layer is down 40 to 130 cm and is composed of facets, surface hoar and a sun crust on solar aspects. This interface is likely most problematic on south facing slopes.Two deeper weak layers that formed in January and December are gradually gaining strength. Several surface hoar and facet layers are buried 1 to 2 m below the surface and there is a crust/ facet interface near the base of the snowpack. No avalanches have been reported on these layers for a few weeks and they are thought to have gone dormant at this time.

Problems

Storm Slabs

40-60 cm of snow from recent storms and strong easterly winds have formed fresh slabs. Triggering is most likely near ridge crests and around mid-slope features like convexities.

Seek out simple well supported terrain below treeline and gather information before stepping out.Even brief periods of direct sun could produce natural avalanches.Avoid freshly wind loaded features.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A persistent weak layer buried up to 130 cm below the surface may be sensitive to human triggering. South-facing terrain is likely to be the most problematic due to the presence of a slippery buried sun crust.

Start with conservative lines and watch for clues of instability.If triggered, storm slab avalanches in motion may step down resulting in large avalanches.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Mar 5th, 2018 2:00PM