Avalanche Forecast

Issued: Apr 12th, 2013 10:37AM

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

pgoddard, Avalanche Canada

South Columbia.

Snowfall amounts for Friday night are uncertain. Danger could spike to HIGH by Saturday if we get more than forecast.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Saturday: Overnight snowfall tapering off to a cool and unsettled flow with light snow. Strong NW winds easing. Freezing level around 1200 m, dropping to 300 m overnight.Sunday: Cold and unstable weather, with light snow. Light N winds. Freezing level around 1000 m.Monday: Cold and unstable weather, with light snow. Light winds. Freezing level around 1700 m.

Avalanche Summary

A natural avalanche cycle to size 2.5 occurred on Wednesday in response to storm loading on all aspects in the alpine. Skiers triggered several size 1-2 wind slabs on N to NE aspects on Thursday. Many of these failed at the base of the recent storm snow on crust interfaces. Some observers mentioned solar-triggered avalanches as well.

Snowpack Summary

Snowfall on Friday night is expected to create new storm/wind slabs, especially near ridge top. This will add to existing storm slab and wind slab problems at alpine and treeline elevations. A surface hoar interface is buried within the upper metre or so of the snowpack, mainly on high-elevation northerly aspects. It may be slowly gaining some strength, but these slopes should still be treated with suspicion. On other slopes, recent storm snow overlies a crust, with a variable bond. At low elevations, previously rain-soaked snow is likely to now be refrozen and strong.

Problems

Storm Slabs

Snowfall on Friday night is expected to create new storm slabs, especially near ridge top and on slopes in the lee of the wind.

Avoid freshly wind loaded features.>Choose well supported terrain without convexities.>Pay attention to overhead hazards like cornices.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

A layer of surface hoar is buried about a metre down, mainly on high northerly aspects. A surface avalanche stepping down, cornice fall, or the weight of a person from a thin-spot trigger point could trigger it.

Be aware of thin areas that may propagate to deeper instabilites.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1 - 6

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