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Archived

Avalanche Forecast

Mar 15th, 2016–Mar 16th, 2016
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
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

Regions: Northwest Inland.

Lingering wind slabs and cornices are expected to become weak with sun exposure and afternoon warming.  Use extra caution on sun exposed slopes when the solar radiation is strong.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A mix of sun and cloud is expected for Wednesday with afternoon freezing levels around 900m and light alpine winds from the northwest. Sunny conditions are expected for Thursday with afternoon freezing levels around 1100m and light outflow winds in the alpine. A mix of sun and cloud is forecast for Friday with freezing levels climbing to around 1500m and moderate outflow winds in the alpine.

Avalanche Summary

On Monday, a natural cornice release triggered a size 1.5 wind slab on a northwest aspect at 1750m which was 25cm thick. Skiers were triggering size 1 soft slabs on steep leeward slopes. In the far north of the region, a natural cornice release triggered a size 2.5 slab which released on the early March surface hoar layer.

Snowpack Summary

In sheltered areas at higher elevations, 20-30cm of low density snow can be found. Recent southerly winds have redistributed the surface snow in exposed terrain formed wind slabs and cornices in leeward terrain. On Monday, moist snow was reported up to 1650m elevation on southern aspects and up to 1200m on northern aspects. A layer of surface hoar from early March can be found down 60-80cm but only seems to be a problem for the northern half of the region. Professional operators are still tracking two deep weak layers from early-January and early-February which can be found down about 1m or more. These layers have been dormant for a couple weeks but could wake up with heavy storm loading, substantial warming, or a heavy trigger like a cornice fall. In the far north of the region, there is an isolated weakness at the base of the snowpack that has been responsible for some very large and destructive avalanches.

Avalanche Problems

Wind Slabs

Lingering wind slabs are expected to remain reactive to human-triggering. Sun and afternoon warming may increase the sensitivity of triggering a slab.
Use ridges or ribs to avoid pockets of wind loaded snow.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 4

Cornices

Cornices are reported to be large and weak. Natural cornice releases are possible with sun exposure and warming.
Extra caution needed around cornices with current conditions.>Cornices become weak with daytime heating. >

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

Elevations: Alpine.

Likelihood: Possible

Expected Size: 1 - 5

Deep Persistent Slabs

Three buried weaknesses remain a concern, mainly in the north of the region (see snowpack discussion for details). Isolated very large avalanches remain a possibility, especially with a heavy trigger like a falling cornice.
Be aware of the potential for full depth avalanches due to deeply buried weak layers. >Be aware of thin areas that may propagate to deeper instabilites. >

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 3 - 6