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Avalanche Forecast

Archived

Nov 26th, 2012–Nov 27th, 2012

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

Regions

South Columbia.

Confidence

Poor - Due to limited field observations

Weather Forecast

Tuesday: Mostly clear skies / Moderate to strong northwesterly winds / Freezing level at 1300mWednesday: Increasing cloud throughout the day with light snowfall developing by the evening / Strong southwest winds / Freezing level at 1400mThursday: Continued snowfall with heavier accumulations in the north of the region / Strong southwest winds / Freezing level at 1400m

Avalanche Summary

In a neighboring region there was a report of a size 2 natural loose snow avalanche. It occurred on a southeast aspect at about 2400m.

Snowpack Summary

Snow accumulations from last week varied from 25-50 cm, although the resulting storm/wind slabs have most likely gained considerable strength with the more recent break in the weather.A buried surface hoar layer has been reported. Although I am unsure of its distribution throughout the region, the average depth is about 60 cm from the surface and seems to exist in specific, sheltered locations. Below this (down 80-110 cm) sits the early November crust. Test results on this layer have been variable; however, some have shown sudden planar pops on facetted crystals at this crust interface, or within the crust sandwich.The snowpack depth in the alpine ranges from 130-225 cm. Treeline near 150 cm. A sharp transition exists below treeline, where the snowpack peters out around 1300 m.

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.