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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

South Columbia.

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 moderate and westerly / Freezing level dropping from 1500m to 1200mSaturday: Light snowfall / Moderate west winds / Freezing level at 1200mSunday: Light snowfall / Light northwest winds / Freezing level at surface

Avalanche Summary

Natural storm slab avalanches to size 2.5 were reported yesterday. The occurred on a variety of aspects at treeline and above, and in some cases failed on the recently buried surface hoar.

Snowpack Summary

A deep and cohesive storm slab continues to develop at higher elevations while rain has saturated the snowpack in areas below treeline. The newly formed storm slab overlies a few older surfaces which include weak surface hoar on shaded aspects, and a sun crust on solar aspects. This interface was reported to be highly reactive in recent days with avalanches triggered from remote locations and propagating long distances. The weak layer of surface hoar buried on February 12th is now down about 100-150 cm. Some areas report that this layer is rounding and getting harder to shear in snow profile tests, but continues to give planar shears when it does fail. The new load of storm snow may cause another cycle of natural activity at this interface.

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.