Avalanche Forecast

Issued: Apr 12th, 2013 10:29AM

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

pgoddard, Avalanche Canada

Purcells.

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. Moderate W winds. Freezing level around 1000 m.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 or calm winds. Freezing level around 1500 m.

Avalanche Summary

Observations have been limited during Wednesday’s storm, when a natural avalanche cycle is expected to have occurred. On Thursday, a cornice fall triggered a size 2.5 slab. Skiers also triggered size 1 slabs. These events were on NE aspects above 2300 m.

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 of the snowpack, mainly on high-elevation northerly aspects. It is still producing moderate, sudden results in snowpack tests, and these slopes should 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: Alpine, Treeline.

Likelihood

Possible - 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.

Carefully evaluate and use caution around thin snowpack areas.>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