Avalanche Forecast

Issued: Apr 21st, 2013 10:30AM

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

swerner, Avalanche Canada

Purcells.

The Public Avalanche Forecasts come to an end on Monday. Starting Tuesday you can find spring messaging under the "Forecast Details" tab below.See you next Season!

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

An upper ridge stalls off the coast bringing sunny skies and dry cool conditions through Tuesday. By mid-week freezing levels will rise to 2000 m.Monday: Mostly sunny skies. Ridgetop winds will blow light from the NW and freezing levels will rise to 1800 m. Tuesday: Broken cloud cover and a chance of flurries. Ridgetop winds moderate from the NW and freezing levels 1800 m. Wednesday: The stationary ridge of high pressure continues bringing sunny skies and freezing levels up to 2000 m. Ridgetop winds will blow light from the SW.

Avalanche Summary

No new avalanche activity has been reported.On Friday, numerous size 1.5-2 wind slab avalanches were skier triggered. All of which were from 35-40 degree slopes on NE aspects above 2100 m. All of these avalanches failed within the recent storm snow interface approximately 30 cm down, and on the early April interface around 80 cm down. One of these was remotely triggered from 15 m away, size 2.

Snowpack Summary

Up to 20 cm of new snow overlies a variety of old snow surfaces. These consist of melt-freeze crusts, buried surface hoar and surface facets. Touchy wind slabs exist on lee slopes and behind terrain features. Cornices on ridgelines or huge, and will likely become weak with daytime warming. They pose a threat to slopes below. Surface snow will likely become wet and deteriorate on solar aspects.Deeper in the snowpack a weak interface buried in early April is down about 60-120 cm and consists of a crust and surface hoar. Earlier this week, very large avalanches were reactive on this interface in neighboring regions. The bond may be getting stronger, but I would still use caution and be suspicious of large, steep upper elevation slopes.

Problems

Wind Slabs

Touchy wind slabs exist on lee slopes at treeline and above. Cornices are huge and remain a concern, especially with daytime warming which will likely make them weak. They threaten slopes below.

Use ridges or ribs to avoid pockets of wind loaded snow.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

Loose wet avalanche activity is likely with rising freezing levels and clear sunny skies. Conditions can change quickly with timing, aspect and elevation.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

A weak interface buried in the upper metre of the snowpack can create surprisingly large avalanches. It's been reactive in nearby regions, and remains a concern with professionals. Be cautious in steep, alpine terrain.

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

Expected Size

1 - 6

Valid until: Apr 22nd, 2013 2:00PM