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Avalanche Forecast

Archived

Nov 30th, 2017–Dec 1st, 2017

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Inland.

The late October crust near the base of the snowpack is reactive to rider triggers producing large avalanches. You could trigger this from a significant distance away. Heads up out there as this problem will likely persist.

Confidence

Low - Due to the number and quality of field observations

Weather Forecast

Friday: Cloudy with possible flurries. Strong ridgetop winds from the West. Alpine temperature -10. Freezing level 500 m and dropping.Saturday: Mix of sun and cloud. Light ridgetop winds from the North West. Alpine temperature -15. Freezing level valley bottom.Sunday: Mostly sunny with some residual cloud. Strong ridgetop winds from the North West. Alpine temperature -12. Freezing level valley bottom. Visit the Mountain Weather Forecast for more details.

Avalanche Summary

On Tuesday, skiers up Skilokis Creek area 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 facet layer just above the late October crust near the base of the snowpack. The persistent slab was 80 cm deep, 120 m wide and ran 300 m in length. The week before that, 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

Average Snowpack depths are 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. This crust extends well into alpine elevations. Below this crust is a well settled mid pack that sits on the widespread late October crust near the base of the snowpack at all elevations. This late October "crust/facet combo" layer has been very reactive to rider triggers producing large avalanches.

Problems

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.