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Avalanche Forecast

Archived

Mar 14th, 2013–Mar 15th, 2013

Alpine
Natural and human triggered avalanches likely.
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 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

Cariboos.

Confidence

Fair - Timing of incoming weather is uncertain on Friday

Weather Forecast

Overnight Thursday and Friday: Heavy precipitation becoming light on Friday / Moderate to strong southwest winds becoming westerly / Freezing level dropping from 1800m to 1200mSaturday: Light snowfall / Moderate west winds / Freezing level at 1200mSunday: Light snowfall / Light northwest winds / Freezing level at surface

Avalanche Summary

Several natural storm slab avalanches to size 2.5 were reported from the region on Wednesday. They occurred on various aspects and elevations. At least 1 of the reported avalanches failed on the recently buried surface hoar. That avalanche was on a north aspect at 1900m and had a crown of 60-100cm. I would expect fairly limited observations with reduced visibility on Thursday.

Snowpack Summary

Strong Southwest winds, new snow, and warming temperatures are contributing to an ongoing storm slab problem. The new storm snow overlies a widespread layer of surface hoar that developed during the recent clear weather. Sun crusts also developed during the clear weather on solar aspects up to about 2000 metres. Some areas had strong winds before the surface hoar was buried, so its distribution may be specific to sheltered and shaded terrain features. There is still concern for the buried weak layer of surface hoar from February 12th that is now down more than a metre in most places. The forecast new load of snow and wind may overload this deeply buried weak layer in areas that did not slide after the last storm.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.