Avalanche Forecast

Issued: Feb 27th, 2014 8:26AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is considerable. 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

Unsettled conditions are expected for Friday before arctic air moves into the region Friday evening. On Saturday and Sunday, weak disturbance from the south will mix with the cold air and may result in light scattered flurries.Friday: Mostly cloudy with sunny breaks, scattered flurries 2-8cm, treeline temperature around -8C, ridgetop winds 15-25 km/h variableSaturday: A mix of sun and cloud, scattered flurries 2-4cm, treeline temperature around -15C, ridgetop winds 10-20 km/h NE, outflow winds at valley bottomSunday: Mostly cloudy with sunny breaks, scattered flurries 2-4cm, treeline temperature around -12C, ridgetop winds 30-50 km/h SW

Avalanche Summary

Wednesday saw natural activity up to size 3 on SE through SW aspects triggered by solar warming.Â Also reported were two skier remote triggered avalanches sized 1.5 and 2.Â These were both triggered from 5m away and were 70cm deep.

Snowpack Summary

The primary concern is a ~1m thick slab 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.

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

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.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Feb 28th, 2014 2:00PM