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Archived

Avalanche Forecast

Apr 20th, 2013–Apr 21st, 2013
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
Below Threshold
The avalanche danger rating in the alpine will be below threshold
Treeline
Below Threshold
The avalanche danger rating at treeline will be below threshold
Below Treeline
Below Threshold
The avalanche danger rating below treeline will be below threshold

Regions: Purcells.

The Public Avalanche Forecasts and Danger Ratings will come to an end on Tuesday. General spring messaging will be found under the Forecast Details tab.

Confidence

Fair - Due to limited field observations

Weather Forecast

The Interior will remain under a cool, dry North-West flow through to Tuesday. A slow warming trend will persist through the end of next week.Sunday: Scattered-broken cloud cover, allowing some sunshine through.  Ridgetop winds will blow light from the North. Freezing levels 1100 m and falling to valley bottom overnight.Monday/Tuesday: Mostly clear, sunny skies. Ridgetop winds will blow light from the NW. Freezing levels 1800 m in the afternoon.

Avalanche Summary

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 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 have grown large, and pose a threat to slopes below.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.

Avalanche Problems

Wind Slabs

Touchy wind slabs exist on lee slopes at treeline and above. Cornices have grown very large, so be aware of overhead hazards and stay back on ridgelines.
Use ridges or ribs to avoid pockets of wind loaded snow.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

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

Elevations: Alpine, Treeline.

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 - Possible

Expected Size: 1 - 6