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Avalanche Forecast

Archived

Dec 14th, 2012–Dec 15th, 2012

Alpine
Natural avalanches possible, human triggered probable.
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.
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 - Track of incoming weather is uncertain

Weather Forecast

Synopsis: A series of weakened frontal systems will affect southern interior over the next few days. The strongest system is forecast to affect the region on Monday.Saturday: Light snow – 5-10 cm. Winds should be moderate from the SW. The freezing level should remain near valley bottom. Sunday: Lingering flurries with snow possibly developing overnight. Winds remain moderate from the W-SW. Freezing level near valley bottom. Monday: Moderate snow. Freezing level could jump to 800 m.

Avalanche Summary

A few small soft slabs were skier triggered on East and South aspects, and several small loose snow avalanches were reported in steep terrain. An older (approximately from Dec. 10th) natural slab avalanche size 2.5 was also observed on an East facing windloaded convex slope. The crown was an average of 60 cm deep. There was also multiple releases from explosives that ran in the new snow from North West to South East facing slopes.

Snowpack Summary

Wind slabs remain a concern in exposed lee terrain in the alpine and at treeline. The new snow is also burying some older deeper windslabs on northerly aspects in the alpine. Overall, the upper snowpack is reported to be settling well. The November 28 surface hoar down 100-140 cm (between 1500 and 2000 m) is producing moderate to no results in snowpack tests. The early November crust, down 150-200 cm, has produced occasional sudden results in snowpack tests. Professionals are still cautious about these lingering persistent slab problems, but the likelihood of triggering continues to decrease as the overlying snowpack builds and continues to gain strength.

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.