Avalanche Forecast

Issued: Feb 28th, 2014 8:19AM

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

rbuhler, Avalanche Canada

Kootenay Boundary.

We are entering a 'low probability/high consequence' phase with a tricky persistent weak layer. Check out this new blog post on difficult decision making and current conditions.Avoid large, unsupported slopes, especially on north aspects.

Summary

Confidence

Fair

Weather Forecast

An arctic ridge of high pressure should dominate for Saturday resulting in mainly clear, cold conditions. Unsettled conditions are expected for Sunday. The edge of a weak low pressure system from the coast should result in light snowfall on Sunday night/Monday morning but the timing/track/intensity still remains somewhat uncertain.Saturday: A mix of sun and cloud, treeline temperature around -15C, ridgetop wind light NESunday: Cloudy with sunny breaks, scattered flurries 0-2cm, treeline temperature around -12C, ridgetop wind increasing to 20-30 km/h SE-SW during the daySun. Night/Monday: Cloudy in the morning, partial clearing during the day, snowfall 3-8cm overnight, treeline temperature around -3C, ridgetop wind 30-40 SW-W

Avalanche Summary

On Thursday, two skier accidental avalanches were reported in the KB.Â These were size 1.5 and 2.Â The deeper released down 70cm.Â Also reported were three remotely triggered avalanches up to size 2.Â The furthest away trigger was 40m.Â Two natural avalanches were reported up to size 2.5 and were likely triggered by the sun.

Snowpack Summary

The primary concern is a persistent slab (typical thickness 50-90cm) from the last series of storms that is sitting on a stubborn persistent weak layer consisting of facets, surface hoar, melt-freeze crusts, or any combination of these. This weak layer is widespread at all elevations and aspects. Recent test results are suggesting that the layer is still easy to trigger in some areas but may becoming harder to trigger in other areas. We are still receiving isolated reports of large settlements or whumpfing which suggests the layer still has the potential for large propagations. In many areas the layer has the potential to produce large, destructive avalanches. The phase we are now entering is referred to a 'low probability/high consequence' problem. Continue to use conservative terrain choices until you are sure the layer is no longer unstable in your local area. Variable winds from the southwest through north have created touchy wind slabs on leeward slopes and cross-loaded features. In wind-loaded areas, slabs up to 2m thick may overlie the persistent weak layer.On south aspects, a sun crust has formed on the surface. New surface hoar formation 5-10mm has been observed.

Problems

Persistent Slabs

Expect the deeply buried weak layers to continue to produce large and destructive avalanches. Many slopes are still primed for human triggering and remain a concern on all aspects and elevations.

Avoid unsupported slopes.>Use conservative route selection and resist venturing out into complex terrain, even if you observe no obvious signs of unstable snow.>Remote triggering is a big concern, be aware of the potential for wide propagations and large, destructive avalanches at all elevations.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

3 - 6

Wind Slabs

Older wind slabs still exist in many lee terrain features but are becoming harder to trigger. Some isolated areas may have thin, touchy wind slabs from more recent wind. Weak cornices also remain a concern in isolated areas.

Be cautious as you transition into wind affected terrain.>Caution in lee and cross-loaded terrain near ridge crests.>Extra caution needed around cornices with current conditions.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Mar 1st, 2014 2:00PM