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Avalanche Forecast

Archived

Feb 5th, 2016–Feb 6th, 2016

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

Regions

South Rockies.

New snow and wind have created fresh wind slabs that are ripe for human triggering.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

Expecting 5-15cm of snow by Saturday Morning and then drying out for remainder of period. Friday's snow will be accompanied by strong southwesterly winds. Winds remain moderate westerly on Saturday morning before easing off for the remainder of the period. Freezing levels remain at valley bottom until they rise sharply to near 2000m on Monday.

Avalanche Summary

A size 2 cornice triggered persistent slab which likely failed on a surface hoar layer buried in early January was observed on Thursday.

Snowpack Summary

5cm of new snow overnight with strong gusty winds in variable directions have created fresh 20-30cm wind slabs in areas you might not normally expect to find them such as aspects that are generally windward and well below ridge tops. A persistent weak layer of buried surface hoar can be found at variable depths depending on elevation. A weak crust/facet layer from early-December can typically be found down over 1m. Below 1700m the most recent snow hides a melt-freeze crust.

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.