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Archived

Avalanche Forecast

Nov 23rd, 2017–Nov 24th, 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
2: Moderate
The avalanche danger rating at treeline will be moderate
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.

A complex snowpack has begun to take shape in the Northwest. Choose terrain that is unlikely to release a storm slab and you'll likely avoid triggering the more dangerous persistent slab lurking beneath it.

Confidence

Low - Due to the number of field observations

Weather Forecast

Friday: Mainly cloudy with scattered flurries and a trace to 5 cm of new snow. Moderate to strong southwest winds. Alpine temperatures around -5.Saturday: Mainly cloudy with scattered flurries and a approximately 5 cm of new snow. Moderate south winds. Alpine temperatures around -4.Sunday: Cloudy with isolated flurries and a trace to 5 cm of new snow. Moderate south winds. Alpine temperatures of -3.

Avalanche Summary

One report from Wednesday discussed several estimated Size 2.5-3 avalanches observed on the Kathlyn face of Hudson Bay Mountain. No other new avalanches have been reported, which almost certainly owes more to a lack of observers than a lack of avalanche activity and potential. Please post your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Snowpack depths over the region are above average for late November, with approximately 150 cm of settled snow present at treeline elevations and above. Stormy weather over the mid-week delivered about 30 cm of new snow to the region, forming storm slabs which are expected to be particularly reactive in open terrain where wind effects promote more variable loading. Mid-treeline and lower elevations did receive some precipitation as rain toward the end of the storm, but his thin rain layer is not expected to offer much bridging strength to the snowpack. About 20-30 cm of recent storm snow lies below this week's accumulations and above the widespread late October crust. The October crust is present near the base of the snowpack at all elevations and features a layer of weak, sugary grains above it. This "crust/facet combo" layer remains an ongoing concern for step-down potential from large triggers such as a storm slab release. The crust is less of a concern below treeline where it is broken up by vegetation near the ground.

Avalanche Problems

Storm Slabs

Recent stormy weather has been building touchy storm slabs. The problem is widespread but you can expect slabs to be especially reactive in wind affected areas with more variable snow distribution
The new snow will require several days to settle and stabilize.Avoid steep convexities and areas with more variable snow distribution.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 3

Deep Persistent Slabs

A crust that formed in October exists near the base of the snowpack and a layer of weak, sugary snow has developed above it. This layer may react to a heavy trigger such as a storm slab release. This would produce a very large, destructive avalanche.
If triggered, storm slabs may step down to deeper layers and result in large avalanches.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

Expected Size: 2 - 3