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Archived

Avalanche Forecast

Jan 19th, 2018–Jan 20th, 2018
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
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.

Human triggering of sensitive weak layers is likely. Careful evaluation of the snowpack is required for safe travel.

Weather Forecast

Cloudy with sunny periods and isolated flurries bringing trace amounts of precipitation today.  Alpine temperatures will be steady around -8 with freezing levels reaching 1000m.  A series of fronts continues to bring light snow to Rogers Pass through the weekend, with 4cm on Saturday, 9cm on Sunday and 7cm on Monday.  Expect Moderate SW Winds.

Snowpack Summary

Around 30cm of new storm snow sits atop the January 16 surface hoar layer. Warm temps and mod-strong S-SW has contributed to slab formation in the upper snowpack. The December 15 surface hoar is approximately 100cm down and is highly visible in profiles. This deeper instability is still producing sudden planar results in stability tests.

Avalanche Summary

A natural avalanche cycle accompanied strong winds yesterday morning with several size 2-3 avalanches occurring in steep north facing alpine paths.

Confidence

Intensity of incoming weather systems is uncertain

Avalanche Problems

Storm Slabs

The Jan 16 surface hoar is widespread and buried 30cm. Incremental loading combined with wind action has led to slab development over this weak interface. The January 4th surface hoar is down 60cm and could be triggered by a storm slab avalanche.
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: All elevations.

Likelihood: Likely

Expected Size: 1.5 - 2.5

Persistent Slabs

The Dec 15th layer is down 100cm. After a month under the snow, this surface hoar remains widespread and well-preserved. Daily snowfalls add up. This incremental loading can increase the sensitivity of deep layers that may be forgotten, but not gone.
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