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Avalanche Forecast

Archived

Apr 17th, 2013–Apr 18th, 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 possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Purcells.

If you have any snowpack or avalanche observations, feel free to send them to [email protected]. We'd love to hear from you.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Thursday: Overcast. Light precipitation amounts. Ridgetop winds light-moderate from the West. Freezing levels rising to 1900 m. Friday: Overcast. Light precipitation amounts. Ridgetop winds moderate from the West. Freezing levels 1900 m. Saturday: Overcast. Light-moderate precipitation amounts. Ridgetop winds light- moderate from the NW. Freezing levels 1600 m and falling to valley bottom overnight.

Avalanche Summary

On Tuesday, a natural size 2 cornice fall was reported from an East aspect at 2400 m. This failure occurred under the influence of the sun and did not pull a slab on the slope below. In the adjacent region a size 2 slab avalanche was skier triggered on a NW aspect at 2500 m. The hard slab failed 3 m above the skier. There were no injuries. On Sunday, a naturally triggered size 2.5 slab failed on a buried crust. In Glacier National Park, skiers triggered a size 3 slab on a buried crust on an east aspect in the alpine on Monday.

Snowpack Summary

Recent storm snow and variable winds have formed wind slabs at treeline and above. Cornices on ridgelines have grown large, and pose a threat to slopes below.A weak interface buried early April is down about 60-120 cm and consists of a crust on solar aspects, and surface hoar on high-elevation northerly aspects. The slab above this interface may be reaching it's tipping point with additional loading from forecast snow and wind.

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.