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Avalanche Forecast

Archived

Mar 12th, 2013–Mar 13th, 2013

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Kootenay Boundary.

Warm temperatures and heavy precipitation are increasing the avalanche danger in the days to come. Good time to avoid avalanche terrain or to make very conservative terrain choices out there. 

Confidence

Fair - Forecast snowfall amounts are uncertain for the entire period

Weather Forecast

Tuesday night and Wednesday: The strong Westerly flow bringing significant precipitation amounts into the interior should taper off a little tonight but should keep delivering moisture until Friday. Amounts could be around 30 mm in water equivalent till tomorrow evening with winds blowing strong from the W. Freezing levels are expected to rise to close to 2000 m. during the day and stay high until Friday.Thursday: Similar amount of precipitation and freezing level is expected for Thursday with strong winds switching from the SW.Friday: The Westerly flow is forecasted to weaken and precipitation to taper off. Freezing levels and wind speeds should also start to drop.

Avalanche Summary

Yesterday, several solar induced small loose avalanches and also some small slab avalanches over convex features in wind effected were triggered by skiers. More and bigger avalanches are expected in the days to come.

Snowpack Summary

Currently, 5-10 cm of new snow overlies a variety of surfaces; hard wind slabs lee of NW-SW winds in alpine and treeline features, a well developed surface hoar in shaded areas above 1700 m., a melt-freeze crust below that elevation and a 3 cm sun crust on solar aspects at all elevations. The forecasted precipitation and warm temperatures will add a good load to the snowpack (could be another 30 mm in water equivalent till tomorrow night). The variety of surfaces described earlier are already showing reactivity to this new load and creating a good failure plane for avalanches to slide on. With freezing levels rising again tomorrow, the new dryer snow layer at the upper below treeline and treeline elevation band (between ~1500 m. and ~2000 m.). could get soaked and create wetslabs and loose wet avalanches. The surface hoar persistent weak layer buried down up to 100 cm is still producing some sudden planar snowpack test results where it is not covered by a thick melt freeze crust bridging it. This layer could be triggered by the heavy load in the coming days.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.