Archived

Avalanche Forecast

Apr 28th, 2013–Apr 29th, 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

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

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

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Glacier.

Weather Forecast

A weak ridge of high pressure will allow a few sunny breaks, with showers and freezing levels around 1900m. Strong S-SW winds will continue. Overnight a cold front will bring up to 13mm of precip with freezing levels lowering to 1000m. Light precip and broken clouds are expected through Tuesday as another ridge starts to build off the coast.

Snowpack Summary

13mm of rain at Rogers Pass, with freezing levels hovering around 1900m over the last 24hrs. Surface wet grains overly a near isothermal snowpack with various crusts/PWL in top meter. ~20cm of storm snow above 1900m will have been transported by strong S'ly winds, loading lee slopes and forming pockets of windslab which may bond poorly.

Avalanche Summary

Warm temps and rain triggered several natural avalanches yesterday. Over the last 2 days size 2-2.5 loose, wet avalanches have been occurring on all aspects, from start zones of 2000-2700m. Cornice failures remain a concern for triggering slab avalanches, mostly failing on PWL's in the top meter.

Confidence

Timing, track, or intensity of incoming weather system is uncertain

Avalanche Problems

Wind Slabs

Sustained strong S'ly winds and new snow above 1900m available for transport are creating wind slabs and loaded pockets of snow. Continued wind loading may trigger slabs. Large cornices have formed and may fail due to warm temps and rain.

Be cautious as you transition into wind affected terrain.Give cornices a wide berth when travelling on or below ridges.

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

Elevations: Alpine.

Likelihood: Possible

Expected Size: 2 - 3

Storm Slabs

Up to 20cm of heavy storm snow has fallen over the last 48hrs above 1900m. This overlies moist, isothermal snow and crusts and may bond poorly. There are few alpine observations, but mild temps and strong winds will have added to the slab properties.

Dig down to find and test weak layers before committing to a line.Whumpfing, shooting cracks and recent avalanches are all strong inicators of unstable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 3

Loose Wet

Rain to ridgetop, turned to snow above 1900m overnight. The rain should taper off today, but loose wet avalanches are possible; most likely triggered by high elevation slabs entraining moist snow or during sunny breaks.

Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 1 - 2