Archived

Avalanche Forecast

Mar 17th, 2016–Mar 18th, 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.

Take a conservative approach when the sun is beating down or it feels balmy, especially if you're not sure about the existence and sensitivity of buried persistent weaknesses.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

FRIDAY: Mainly sunny. The freezing level should jump to around 1600-1700 m and ridge winds are moderate from the SE. SATURDAY: Mainly cloudy with sunny breaks. The freezing level dips to 1100 m but climbs back to 1600 m late in the day. Winds should be light. SUNDAY: A mix of sun and cloud. The freezing level is near 1700 m and winds are light or moderate from the east.

Avalanche Summary

Wind-loaded N-E facing alpine slopes were reactive skier triggering with wind slabs up to size 1.5 in parts of the region on Tuesday. 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. South facing slopes could be capped a sun crust or moist snow depending on the time of day. 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

Variable and shifting winds may have created fresh wind slabs on a variety of aspects in exposed terrain. Sun and warming could increase the sensitivity of triggering this problem.

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