Archived

Avalanche Forecast

Mar 19th, 2017–Mar 20th, 2017

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.

Huge changes have impacted the snowpack in the last week and it needs time adjust to the new loads. A careful, cautious approach to assess backcountry conditions needs to be followed to stay safe the next few days.

Weather Forecast

Today will bring a reprieve from the stormy onslaught. Expect a mix of sun and cloud with flurries, an alpine high of -11*C, and freezing levels staying below 800m. Winds will back off to moderate from the west. More of the same on Monday, with freezing levels rising to 1100m.

Snowpack Summary

An intense front finished off a week of storms yesterday, with heavy rain/snow and extreme SW winds (100+ km/h). A rain crust will be prevalent below ~1600m, and widespread wind and storm slabs have formed at tree-line and alpine elevations. Below this, warm, rapidly settling storm slabs are widespread at all elevations and aspects.

Avalanche Summary

Natural and artillery controlled avalanches to size 4 were observed in the highway corridor yesterday. The biggest avalanche was Macdonald West Shoulder failing simultaneously in 4 start zones, ripping through mature timber and running to the valley floor. We did not patrol the backcountry yesterday, but suspect the same results there.

Confidence

Due to the number of field observations

Avalanche Problems

Storm Slabs

Heavy snowfall and extreme SW winds formed reactive storm slabs at tree-line and alpine elevations. These overlie various weak interfaces in the upper snowpack and need time to readjust to the new load.

The new snow will require several days to settle and stabilize.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 2 - 4

Persistent Slabs

Persistent deep layers made a triumphant return during our most recent avalanche cycle and they remain a cause for concern. As surface instabilities fail, avalanches can easily step down to weak layers from late February, or deeper in shallow areas.

Watch for whumpfing, hollow sounds, and shooting cracks.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 3 - 4

Cornices

The week's worth of warm snow with constant SW winds has built up some very large cornices along ridge-tops. These beasts should be considered fragile and they would be a HUGE trigger to start a large avalanche.

Pay attention to overhead hazards like cornices which could easily trigger deep slabs.Minimize exposure to overhead hazard from cornices.

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

Elevations: Alpine.

Likelihood: Possible

Expected Size: 2 - 4