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Avalanche Forecast

Archived

Dec 28th, 2013–Dec 29th, 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 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.

Regions

Northwest Inland.

Confidence

Poor - Due to the number of field observations

Weather Forecast

Tonight and Sunday: Mainly cloudy with light snow – 5-10 cm. The freezing level is around 1000 m but there is a chance of an above freezing layer near 1500 m. Winds are moderate to strong from the W-SW. Monday: Periods of snow – around 10 cm. The freezing level is near 1000 m and winds are moderate from the SW. Tuesday: Mainly cloudy with a chance of flurries and sunny breaks late in the day. The freezing level is near valley bottom.

Avalanche Summary

No new avalanches have been reported, but observations from the region are very limited. Areas with heavier recent snowfall likely experienced a natural avalanche cycle on Thursday/Friday. Rider triggering remains a concern in steeper terrain and wind loaded features, primarily at and above treeline.

Snowpack Summary

Recent storm snow totals in the region are around 40-50 cm, with moist or wet snow below treeline. Periods of moderate to strong W-SW winds were likely over the past couple days. Expect dense wind slabs in exposed lee terrain and cross-loaded features. Between 40 and 80 cm of snow sits on a crust that extends up to treeline and possibly beyond. This interface was "popping" under easy loads in snowpack tests a few days ago. A new surface rain crust will probably form at lower elevations as temperatures cool tonight. Deeper in the snow pack a layer of facets/surface hoar formed in early December can be found in the top 100cm in the Ashman. The mid and lower snowpack is still structurally weak and faceted. Depth hoar and an early season crust exist near the ground.

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.