Avalanche Forecast

Issued: Mar 3rd, 2018 5:35PM

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.

ghelgeson, Avalanche Canada

Kootenay Boundary.

Previously strong wind has created widespread wind and storm slabs which may remain sensitive to human triggering Sunday. Keep a close eye on the cloud cover, even brief periods of direct sun could initiate natural avalanches.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain on Sunday

Weather Forecast

We are moving into a rather benign weather period that is dominated by high cloud with little significant precipitation expected. SUNDAY: Scattered cloud cover, freezing level rising to around 1000 m, light west/northwest wind, trace of precipitation possible.MONDAY: Scattered cloud cover, freezing level rising to around 1000 m, light west wind, no precipitation expected.TUESDAY: Scattered cloud cover with some mid-day clearing possible, freezing level rising to around 1300 m, light variable wind, no precipitation expected.

Avalanche Summary

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.On Thursday storm slabs to size 2.5 released naturally on a variety of aspects. Human triggered avalanches to size 2 were reported from both west and northeast facing features between 1950 and 2000 m.

Snowpack Summary

10 to 20 cm of new snow fell Friday night with light winds mainly out of the southwest. This adds to the 20 to 60 cm of new snow that fell this week with widely variable winds. Moderate to strong east/southeast winds picked up Thursday night and added some stiffness to the storm slab 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

Easterly winds Thursday formed fresh storm and wind slabs that may remain sensitive to human triggering. Triggering is most likely near ridge crest and around mid slope features like convexities. Up to 20 cm of new snow may be hiding these.

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

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.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Mar 4th, 2018 2:00PM