Archived

Avalanche Forecast

Mar 12th, 2016–Mar 13th, 2016

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

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 slabs and cornices will become weak with sun exposure. Extra caution is required on sun exposed slopes during the heat of the afternoon.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A mix of sun and cloud is expected for Sunday with freezing levels around 1100m in the afternoon and moderate alpine winds from the south. A mix of sun and cloud is expected for Monday with the possibility of scattered flurries. Afternoon freezing levels are expected to be around 1000m and alpine winds are forecast to be light from the south. Light snowfall is currently forecast for Tuesday with freezing level around 1000m and moderate alpine wind from the southwest.

Avalanche Summary

On Friday, a two natural avalanches were reported from steep south facing terrain in the alpine north of Smithers. One was a size 1.5 and the other was a size 3. Skiers were triggering small size 1 slabs with a thickness of 10cm. In the for north, a natural size 2 cornice release was reported. On Thursday, a MIN report from Smithers (https://goo.gl/ssYcRw) describes a natural size 1.5 wind slab that released on a southeast aspect at 1600m and was 30cm thick. Natural activity was also heard but not observed from cliffy terrain in the south of the region. On Wednesday, a few natural wind slabs up to size 2.5 were observed in steep wind-loaded alpine terrain in the south of the region. There was also a large cornice fall that did not trigger a slab on the slope below. In the northern part of the region there were some reports of solar induced slabs to size 3 on south aspects, and natural cornice falls. One cornice fall triggered a size 4 avalanche that released on the ground and cleaned out an entire bowl. It was 1km wide and ran 1.5km.

Snowpack Summary

Roughly 20-40 cm of snow has fallen in the past week, with the highest accumulations occurring in the southwest of the region. Strong ridgetop winds have shifted the new snow into hard or soft wind slabs in exposed terrain, adding to an ongoing wind slab problem. A layer of surface hoar from early January can be found in isolated locations between 60 and 140 cm down. There hasn't been any activity reported on this layer for a couple of weeks now and it is becoming less of a concern. In shallower areas the snowpack sits on a weak base layer of facetted snow. Recently, this layer has been active in the north of the region, responsible for several large avalanches in unsupported alpine terrain.

Avalanche Problems

Wind Slabs

Lingering wind slabs may still be reactive to human triggering. Slabs may become more reactive with daytime warming and/or sun exposure.

Be cautious as you transition into wind affected terrain.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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. These could pop off at any time, but are more likely to fail with continued growth or during brief sunny breaks.

Extra caution needed around cornices with current conditions. >Cornices become weak with daytime heating, so travel early on exposed slopes. >

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

Elevations: Alpine.

Likelihood: Possible

Expected Size: 2 - 5

Deep Persistent Slabs

Isolated large avalanches failing on weak snow at the base of the snowpack remain a possibility. This is a greater concern during sunny breaks or 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 propogate to deeper instabilites.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood: Unlikely - Possible

Expected Size: 3 - 6