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Avalanche Forecast

Archived

Jan 14th, 2013–Jan 15th, 2013

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

Regions

Purcells.

I’ve based this forecast on a weather model that shows rapidly increasing alpine temperatures on Tuesday. If it doesn’t warm up, then these danger ratings are one notch too high.  See the forecasters blog for warming details.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

Tuesday: Winds out of the NW at extreme values. Freezing level rising to 2500m+ around lunch time.  No snow/rain. Clearing skies.Wednesday: Freezing level stays high around 2300m.  Strong/Extreme NW winds persist.  No precip expected.Thursday: Freezing level comes down to 2000m.  Winds switch to westerly strong.  Increasing to westerly extreme in the afternoon.

Avalanche Summary

Most of the region did not see any activity on Sunday. The exception was around the bugaboos where several natural size 2.5's came out of the alpine on a piece of west facing terrain. 

Snowpack Summary

40 - 90 cm of settled storm snow rests on the January 4th interface which consists of small facets, surface hoar (up to 12mm) in sheltered treeline and below treeline areas and sun crust on steep south and west facing slopes. This interface has gained a significant amount of strength.  The concern is that it will spring back to life when the warm temperatures and direct solar come into play midweek. Recent tests on this interface show shears trending towards Resistant Planar. Professionals operating in the region are most concerned about slopes that have not yet avalanched. Wind slabs formed during the last storm are getting old and tired.The deep crust/facet combo from early November is till evident but it is inactive at this point.?

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.