Archived

Avalanche Forecast

Apr 19th, 2013–Apr 20th, 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

2: Moderate

The avalanche danger rating in the alpine will be moderate

Treeline

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: Purcells.

Confidence

Fair - Due to limited field observations

Weather Forecast

An upper trough will move through the Interior tomorrow, while the NW flow will bring cooler, dryer air and decent pulses of precipitation.Saturday: Overcast. Light-moderate precipitation amounts. Ridgetop winds blowing moderate from the NW. Freezing levels near 1600 m.Sunday/Monday: A ridge of high pressure will bring a mix of sun and cloud, with cooling and dryer conditions. Freezing levels will be near 1000 m during the afternoon and falling to valley bottom overnight.

Avalanche Summary

No new avalanche activity has been reported.

Snowpack Summary

Up to 10 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 on solar aspects, and surface hoar on high-elevation northerly aspects. Earlier this week, very large avalanches were reactive on this interface in the neighboring Glacier National Park. 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

Wind slabs exist on a variety of aspects at treeline and above. Cornices have grown very large, so be aware of overhead hazards and stay back on ridgelines.

Avoid lee and cross-loaded terrain near ridge crests.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

Aspects: All aspects.

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