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Avalanche Forecast

Nov 29th, 2017–Nov 30th, 2017
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Northwest Inland.

Be aware of wind slabs at upper elevations as well as a weak layer deep in the snowpack. This layer has produced recent large avalanches and may be triggered by a wind slab release or from a shallow snowpack area.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY: Isolated flurries, accumulation 5-10 cm. Moderate southwest wind. Alpine temperature -6. Freezing level 500 m.FRIDAY: Isolated flurries, accumulation 5-10 cm. Light to moderate southwest wind. Alpine temperature -7. Freezing level 500 m.Saturday: Mix of sun and cloud. Light west wind. Alpine temperature -10. Freezing level 300 m.

Avalanche Summary

Skiers in the Seaton area on Tuesday reported remotely triggering a large (Size 2.5) avalanche from 150 m away as they approached a north-facing, treeline bowl. The avalanche was triggered from a shallow snowpack area and failed on a weak layer of sugary, snow crystals just above the late October crust near the base of the snowpack. Last week several estimated Size 2.5-3 avalanches were observed on the Kathlyn face of Hudson Bay Mountain and are also suspected to have failed on the late October crust. This "crust/facet combo" layer is capable of producing very large avalanche and is expected to remain a layer of concern for some time. Please post your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Snowpack depths over the south of the region average 100-140 cm at treeline elevations, and up to 160 cm in the alpine. Approximately 30-40 cm of recent snow now overlies the supportive November 23 crust that formed last week and is suspected to extended well into alpine elevations. Below this crust is well settled snow and the widespread late October crust, which is present near the base of the snowpack at all elevations and features a layer of weak, sugary grains above it. This late October "crust/facet combo" layer has been reported as the failure layer for recent large avalanches, and has also been producing moderate, sudden compression test results in snowpack tests. This layer will remain a concern for the potential of a slab release to step down to this layer as well as the potential for large propagations triggered from shallow snowpack areas.

Avalanche Problems

Wind Slabs

Recent snow and wind have formed touchy wind slabs. Expect these slabs to be more pronounced at higher elevations. Watch for signs of wind affected snow, whumpfing and cracking.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Watch for signs of instability such as whumpfing, hollow drum-like sounds or shooting cracks.Avoid steep convexities and areas with variable snow distribution.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Deep Persistent Slabs

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer may react to a heavy trigger like a storm slab release and can also be triggered from shallow snowpack areas.
Be cautious in shallow snowpack areas where triggering a deeper layer may be possible.Be aware of the potential for large avalanches due to weak layers at the base of the snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 2 - 3