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Avalanche Forecast

Archived

Jan 20th, 2013–Jan 21st, 2013

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

Regions

Glacier.

Thin cloud should reduce solar effects today. If the clouds break watch for signs, like sluffing off of cliffs, that the snowpack is warming up. Solar triggered avalanches are possible. Minimize exposure to cornices which may be weakened by the sun.

Weather Forecast

Dry and mild conditions will continue due to the ridge of high pressure through Tuesday. Temps will rise to just below 0'C, with moderate to strong S to W winds.  Thin high cloud should reduce solar effects today, but Monday looks clear with strong solar. Later on Tuesday the next system will move in, possibly (hopefully) bringing more snow.

Snowpack Summary

Sustained moderate to strong southerly winds have created pockets of touchy windslab on lee slopes and windeffect on exposed slopes at treeline and above. A layer down 30-50cm has been most reactive on steep solar aspects where it is composed of facets/surface hoar on a crust. Below this the snowpack is well settled and generally strong.

Avalanche Summary

Skiers have reported triggerable hard windslabs. On Friday, a size 1 triggered at the top of "Puff Daddy" on a NE aspect at treeline, fractured 5m above a skier. It was 30cm deep and ran 50m. There continue to be a few large (sz 2-3) natural avalanches observed daily. These have been triggered by windloading and are from paths with lee start zones.

Confidence

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.