Archived

Avalanche Forecast

Dec 13th, 2015–Dec 14th, 2015

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

1: Low

The avalanche danger rating at treeline will be low

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: South Rockies.

The weekend's storm instabilities are expected to linger for a few days.Use extra caution on steep south-facing slopes during the afternoon if the sun is out in full force.

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure will bring dry and mostly sunny conditions on Monday. Freezing levels are expected to be around 1000m in the afternoon and ridgetop winds should be light from the north. A mix of sun and cloud is expected for Tuesday with freezing levels falling to valley bottom and light alpine winds from the NW. Light snowfall is being forecast for Wednesday.

Avalanche Summary

On Friday, ski cutting produced size 1 soft slabs in immediate lee features (generally north through east aspects). On Saturday, explosives and ski cutting produced storm slabs size 1-2 which were typically 20-60cm thick. On Sunday, explosives triggered a few size 2 wind slabs which were typically 30cm thick.

Snowpack Summary

The series of storms last week produced 70-90cm of new snow in the region. A rain crust which formed during the middle of the storm is now down 40-60cm and has become the primary layer of concern during the weekend storm. The early December interface consists of crust, surface hoar, and/or facets and is typically down 70-90cm. Around 20-30cm below this interface is a rain crust from mid-Nov with a thick layer of facets below it. Both the early-Dec and mid-Nov layers have become dormant and are likely being capped at treeline and below by the more recent rain crust layer. However, these layers may still be reactive to heavy triggers such as cornices, explosives, or smaller avalanches stepping down.

Avalanche Problems

Wind Slabs

Recent wind slabs are expected to remain reactive to human-triggering, especially in the leeward side of ridge crests and in wind-loaded chutes. The sun may increase the likelihood of triggering storm instabilities on steep, south-facing slopes.

Be cautious as you transition into wind affected terrain.>Avoid freshly wind loaded features.>

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 2

Persistent Slabs

A weakness buried early-Dec and a rain crust from mid-Nov in the mid-pack are becoming difficult to trigger but are still a concern in isolated areas. Heavy triggers like cornices or avalanches stepping down could result in very large avalanches.

Dig down to find and test weak layers before committing to a line.>Avoid open slopes and convex rolls at and below treeline where persistent weaknesses may be preserved.>Caution around convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 5