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Archived

Avalanche Forecast

Jan 21st, 2018–Jan 22nd, 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
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
3: Considerable
The avalanche danger rating below treeline will be considerable

Regions: Glacier.

Several surface hoar layers in the upper snowpack are sensitive to human triggering. A small avalanche could initiate a deeper instability resulting in a large avalanche.Travel in the Alpine is not recommended.

Weather Forecast

Cloud cover for the day with 5-10cm of snow by tonight. Alpine temps could reach -6  with freezing levels staying below 1200m. Winds at ridge top will be 20km/hr gusting to 70km/hr from the south. There will be several storms rolling through our area over the next few days, with up to 40cm of snow by Thursday morning.

Snowpack Summary

40cm of new storm snow sits atop the January 16 surface hoar layer which is settling quickly and reactive in tests. Previous strong south winds have built pockets of wind slab in the Alpine. The December 15 surface hoar is down 100cm and is highly visible in profiles and still producing sudden planar results in tests.

Avalanche Summary

Several natural avalanches size 2-3.5 came down the north aspect of Mt. Macdonald this morning. The size 3.5 dusted and spread woody debris on the highway for a 100m section. Two sz 2.5 were observed yesterday from the same area originating from steep, rocky terrain.Avalanches originating in the Alpine have the potential to run into valley bottoms.

Confidence

Timing, track, or intensity of incoming weather system is uncertain on Sunday

Avalanche Problems

Storm Slabs

Previous strong south winds combined with recent new snow has built surface slab. This buries the Jan 16 surface hoar which is widespread and found down 40cm. Slabs triggered over this weak layer could propagate far and trigger deeper layers.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Use caution in alpine lees. Recent snowfall mixed with wind loading has created storm slabs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Likely

Expected Size: 1.5 - 2.5

Persistent Slabs

The January 4th surface hoar is down 60cm and the Dec 15th layer is down 100cm. After a month under the snow, this surface hoar remains widespread and well-preserved. These layers should not be overlooked and could be more sensitive in thin areas.
If triggered the storm slabs may step down to deeper layers resulting in large avalanches.Dig down to find and test weak layers before committing to a line.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2 - 3.5