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Avalanche Forecast

Archived

Dec 29th, 2011–Dec 30th, 2011

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

Regions

South Rockies.

Confidence

Fair - Intensity of incoming weather is uncertain on Friday

Weather Forecast

Friday: Snow amounts 5-10cms. Ridgetop winds 75-100km/hr from the West. Freezing levels could rise to 1000m. Saturday/Sunday: A ridge of high pressure is expected to move into the region for the weekend. Mainly sunny skies, and light-moderate winds from the West. Temperatures at 1800m will be near -15.

Avalanche Summary

Natural activity reported today up to size 2 on steep N-NE facing slopes. Some natural low density sluffing in steep, rocky terrain features. Cornice fall on N-NE aspects initiating avalanches up to size 2.

Snowpack Summary

Strong westerly winds, up to 10cms of new snow and warmer temperatures continue forming wind slabs on lee locations. Windward aspects are being stripped, and scoured in the alpine and open treeline. A buried layer of surface hoar lies approximately 30-40cms below the snow surface. This layer is not widespread; it's quite spotty through the region. This layer may be found in isolated, sheltered locations at and below treeline and up to 30mm in size. The total snowpack depth around 1800m is 70cm. We're still dealing with a variable thin snowpack. Thin spot triggering down to the basal facets and depth hoar is still a concern. A well settled mid pack bridges over the basal weaknesses at the ground in deeper snowpack areas.

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.