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Archived

Avalanche Forecast

Feb 18th, 2013–Feb 19th, 2013
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
3: Considerable
The avalanche danger rating below treeline will be considerable
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
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Glacier.

Avalanche danger will be higher when slopes are directly in the sun. Play close attention to overhead hazards; slopes or cornices may fail when receiving strong solar. Loose solar triggered avalanches, or cornice failures may step down deeper.

Weather Forecast

It's clear and calm this morning. Expect solar triggered avalanches, starting on E aspects and following the sun. A cold front will move in this afternoon bringing increasing cloud and rising SW'ly winds. Tuesday should be mostly cloudy, with light winds and flurries. On Wednesday, another upper ridge builds bringing sunny periods.

Snowpack Summary

A very soft slab exists over a thin crust down ~30cm and a widespread surface hoar layer down ~50cm. The surface hoar is most reactive where it is largest; between 1700-1900m; or on steep solar aspects where it sits on a crust. Tests indicate it is likely to be triggered by light loads (easy to moderate, planar/collapses and RB2 whole block).

Avalanche Summary

Clouds reduced solar effects yesterday. When the sun did hit slopes, several size 1.5-2 solar triggered avalanches occurred.  There have been human triggered avalanches up to size 2 on the most recent surface hoar layer. These have occurred on all aspects and elevations, with the avalanches propagating up to 300m wide and traveling fast and far.

Confidence

Avalanche Problems

Persistent Slabs

A touchy surface hoar layer is down ~50cm. Human (even tree bomb) triggered avalanches have occurred daily. Avalanches are increasingly possible with new snow load and mild temperatures making the slab more cohesive.
Choose well supported terrain without convexities.Choose conservative lines and watch for clues of instability.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Wind Slabs

Soft windslabs formed on the immediate lees of ridges above treeline. In wind-affected areas the recent storm snow will be more cohesive. These slabs overlay a touchy surface hoar layer and if triggered, avalanches may propagate widely.
Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2