Avalanche Forecast

Issued: Mar 12th, 2013 10:59AM

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

slemieux, Avalanche Canada

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.

Summary

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

A significant load will add on the snowpack possibly triggering the 100 cm deep surface hoar/sun crust weak layer.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

3 - 7

Storm Slabs

The warm and wet storm is suspected to create new storm slabs, new wind slabs lee of strong SW winds in the alpine and treeline, loose dry avalanches above 2000 m. and wet slabs and loose avalanches below that elevation.

Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.>Avoid exposure to overhead avalanche terrain, as large avalanches may reach runout zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 6

Valid until: Mar 13th, 2013 2:00PM