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Archived

Avalanche Forecast

Dec 17th, 2018–Dec 18th, 2018
Alpine
4: High
The avalanche danger rating in the alpine will be high
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
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
4: High
The avalanche danger rating at treeline will be high
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Glacier.

Avalanche activity is expected to increase as temperatures rise and the storm snow settles into a cohesive slab. Moderate to strong winds are also promoting wind slab development. Human triggering is likely. Stick to conservative, supported terrain.

Weather Forecast

Another day of fresh trail breaking will bring scattered flurries with 5cm of snow accumulation, an alpine high of -4 with winds ranging from 20-50kph from the SW. The freezing level will rise up to 1500m so watch for tree bombs at lower elevations. 25cm of snow forecasted by Tuesday evening and 10cm on Wednesday.

Snowpack Summary

10cm overnight brings our settled storm snow to ~90cm. Fresh wind slab in alpine and open tree line areas. The December 9th persistent weak layer is buried 60-100cm and producing large 'whumphs' and sudden planar test results. The November 21st persistent weak layer is down 120-160cm. Height of snow at treeline is ~ 2m, and ~1m at Rogers Pass.

Avalanche Summary

Numerous avalanches size 2 to 3 were observed at all elevations and aspects over the weekend. A skier-triggered size 1 avalanche off a steep gully sidewall partially buried one person in NRC Gully on Saturday. Large settlements on the Dec 9 layer are producing 'whumphs' that travel for over 100m in open terrain and seem most prevalent at tree line.

Confidence

Avalanche Problems

Wind Slabs

New snow and moderate - strong winds are producing wind slabs and can be found on lee and cross-loaded features in the alpine and tree line and easily triggered on unsupported convex rolls. These slabs sit atop existing storm instabilities.
Avoid convexities and unsupported features.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: North, North East, East, West, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2.5

Persistent Slabs

The December 9 weak layer is down 60-100cm. This layer consists of surface hoar, facets, and sun crust, depending on the aspect and producing sudden planar test results. Natural and human triggered avalanches are still occurring on this layer.
Watch for whumpfing, hollow sounds, and shooting cracks.Avoid open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 2 - 3.5