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Avalanche Forecast

Archived

Mar 22nd, 2017–Mar 23rd, 2017

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

Regions

Glacier.

We are in a tricky Low Probability, High Consequence cycle. The reality is that large, likely un-survivable avalanches will continue to occur sporadically and are very hard to predict. Manage your exposure and be conservative in terrain selection!

Weather Forecast

Unsettled weather continues. Today should be mainly cloudy, with isolated flurries and moderate S'ly winds. Freezing levels will rise to 1700m. Overnight continued flurries will accumulate to ~6cm, with mod to strong SW winds. Thurs should be dry with sunny breaks in the afternoon. Friday should be cloudy with flurries adding up to another 8cm.

Snowpack Summary

Recent storm instabilities are gaining strength. Winds have been shifting directions forming windslabs in alpine lee's and adding to the already huge cornices. Mid February PWL's are now down ~150cm and were reactive during last weeks storm. The basal weakness (Nov 13 crust) has been reactive to large triggers (ie cornices and step-downs).

Avalanche Summary

The snowpack has demonstrated it's potential to produce very destructive avalanches. For example, on Sat Macdonald West Shoulder avalanched naturally ripping out mature timber and running to the valley floor. Sporadic avalanches continue to occur, like this one in the Smart drainage on Monday, showing wide propagation and multiple step down layers.

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.