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Avalanche Forecast

Archived

Jan 26th, 2013–Jan 27th, 2013

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

Regions

Northwest Inland.

Confidence

Poor - Due to limited field observations

Weather Forecast

Sunday: Northwest flows aloft will bring continued snowfall accumulations. Snow amounts 5-10 cm accompanied by strong ridgetop winds from the NW. Alpine temperatures near -8.0 and freezing levels near valley bottom. Monday: A low pressure system over Gulf of Alaska will move onto the north coast bringing moderate precipitation. Snow amounts 10-15 cm with strong NW ridgetop winds. Alpine temperatures near -2 and freezing levels hovering around 700 m. Tuesday: Moderate snowfall amounts expected. Alpine temperatures will fluctuate from -11.0 to an average -4.0 and possibly rising to above zero degrees in areas closest to the coast. Ridgetop winds will shift out of the SW in the light-moderate ranges.

Avalanche Summary

No new natural avalanches have been reported. Several size 1.0 skier triggered avalanches occurred specifically over convex rolls at treeline elevations.

Snowpack Summary

Variable accumulations of new snow continue to build over a variety of old surfaces. These include old hard and soft wind slabs, scoured slopes, blue ice, thin melt-freeze crusts and surface hoar. Many windward slopes are scoured and thin. Recent snowpack tests recently gave generally hard to no results near Smithers. An otherwise strong mid-pack overlies a weak base layer of facets/depth hoar. Triggering of this basal weakness may still be possible from thin spots and/or rocky outcrops. I suggest digging down, or probing the snowpack to get a handle of average snowpack depths, variability and test results. Be cautious on slopes that go thin from thick. The average  snowpack depth is around 100 cm at treeline, but remains quite inconsistent across the region.

Problems

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.

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.