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Avalanche Forecast

Archived

Jan 30th, 2013–Jan 31st, 2013

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.
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.

Confidence

Poor - Due to limited field observations

Weather Forecast

Thursday:  Cloudy, unsettled conditions. Snow amounts up to 10 cm. Ridgetop winds blowing 30-50 km/hr from the West. Alpine temperatures near -2 and freezing levels rising to 800 m.Friday: Continued cloudy skies and snow amounts near 5 cm. Ridgetop winds light from the SW. Alpine temperatures near -2 with freezing levels rising to 900 m.Saturday: Snow amounts 5-10 cm with ridgetop winds light from the South. Alpine temperatures near -3 and freezing levels sitting near 800 m.

Avalanche Summary

Loose dry sluffing from steep terrain. One skier triggered size 2.0 from a NE aspect around 1280 m, from a 40 degree slope.

Snowpack Summary

New storm snow (30-50 cm) is building over a variety of old surfaces including old wind slabs, scoured thin slopes, blue ice, thin melt-freeze crusts and surface hoar. The new storm snow may have a poor bond with the old surfaces buried below. With little observations from the field its hard to get a good handle on possible persistent weak layers. I stress the importance to dig down and become familiar with the snowpack in your neck of the woods. Look for, and test potential weak layers. Observe their reactivity before dropping into your run or line.The average snowpack depth at treeline is near 100 cm but remains quite inconsistent across the region. A strong mid-pack currently overlies a weak base layer of facets/depth hoar. Triggering of this basal weakness may still be possible from thin spots, rocky outcrops or under the weight of larger triggers such as cornice fall and larger amounts of new storm snow.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

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.