Avalanche Forecast

Issued: Apr 18th, 2013 10:24AM

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

Avalanche Canada swerner, Avalanche Canada

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Initially, the approaching frontal system will spread light-moderate precipitation amounts with rising freezing levels. Towards the end of the forecast period a cooling, drying trend will take place before a big warm-up next week.Friday: Overcast with light- moderate precipitation amounts. Ridgetop winds will blow moderate from the SW and freezing levels will rise to 1900 m.Saturday: Overcast with moderate precipitation amounts. Ridgetop winds will blow moderate from the NW and freezing levels near 1400 m then falling to valley bottom overnight.Sunday: Mostly sunny skies with a cooling, drying trend. Freezing levels will rise to 1200 m by the afternoon.

Avalanche Summary

On Wednesday, a remotely triggered  a size 2.5 slab avalanche from a North aspect at 2700 m occurred from the ridgetop. A large whumph was heard and felt with no involvements.

Snowpack Summary

Over the past 2 days, melt-freeze crusts have formed on solar aspects. North aspects remain dry, with new surface hoar development and surface faceting. Forecast snow and wind may build new wind slabs, burying older wind slab problems found at treeline and above. Cornices are very large and remain a concern.In some locations a surface hoar interface exists buried within the upper metre of the snowpack. This is mostly found on northerly aspects at upper elevations.  It may be slowly gaining some strength, but I’d remain suspicious and practice caution around these slopes. On other aspects, the storm snow overlies a crust. This crust interface has recently become reactive in regions further south and may become reactive in your area with additional load.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow and moderate winds will likely build new wind slabs on lee slopes. Buried wind slabs exist on a variety of aspects at treeline and above. Large, looming cornices exist on ridgelines and pose a threat to slopes below.
Stay off recent wind loaded areas until the slope has had a chance to stabilize.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

An icon showing Persistent Slabs
A weak interface is buried about a metre down. A surface avalanche stepping down, cornice fall, or the weight of a person from a thin-spot trigger point could trigger a large and destructive avalanche.
Be aware of thin areas that may propagate to deeper instabilites.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Apr 19th, 2013 2:00PM