Archived

Avalanche Forecast

Dec 7th, 2014–Dec 8th, 2014

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

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

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

Regions: Kootenay Boundary.

A strong Southwest flow is expected to bring strong winds and rapidly rising freezing levels. Expect avalanche danger to increase as the storm develops.

Confidence

Poor - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Increasing cloud is forecast for this evening, with light precipitation starting in the early morning. Southwest winds are expected to build to moderate from the Southwest during the day on Monday. The winds should increase to strong from the Southwest on Tuesday combined with 5- 10 mm of precipitation that will probably be rain up to about 2000 metres elevation. The warm, wet, and windy weather is expected to continue on Wednesday as freezing levels spike up to about 2200 metres elevation.

Avalanche Summary

No new avalanches reported from this region. The new storm slab is the immediate concern for easy human triggering. Avoid freshly wind loaded features at higher elevations. The more complex problem is the lingering persistent weak layer of buried hard rain crusts with weak facets or surface hoar at the interface. Rising freezing levels during the forecast storm combined with the chance of heavy loading from rain or wet snow may be enough to weaken the bond at the crust.

Snowpack Summary

The developing storm slab is variable across the region. In the Monashee range near Big and Little White we have reports of a 25 cm storm slab that has been transported by the wind at higher elevations and it is sitting on a weak layer of facets or surface hoar. This storm slab is giving easy results from light forces in snow profile tests. The new storm slab is reported to be thinner near Nelson where it is sitting on a thin re-frozen rain crust. In the Kootenay Pass area the new storm slab is about 20 cm and may be sitting on surface hoar, and then another layer of about 20 cm (40 cm total) above the hard November 29th crust. The November 20th crust may be anywhere from about 40 cms above the ground in deeper snowpack areas to on the ground or non-existent in shallower snowpack areas. The November 20th crust continues to give moderate planar results in snow profile tests in some areas; that means the right combination of load and terrain features may result in an avalanche down to this buried layer.

Avalanche Problems

Storm Slabs

Forecast wind combined with new snow or rain may result in a touchy storm slab. Watch for conditions changing with elevation.

Avoid convexities, and other unsupported terrain features.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 3

Persistent Slabs

Warming combined with increased loading from new snow or rain may increase the deeply buried slabs sensitivity to human triggers. Watch for thin spots around boulders or small trees that may be easy to trigger and then propagate to deeper areas.

Avoid large alpine features that may result in wide propagations if an avalanche steps down to the deeply buried crust.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 3 - 5