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Avalanche Forecast

Archived

Dec 14th, 2012–Dec 15th, 2012

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 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

Kootenay Boundary.

Confidence

Fair - Intensity 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 to locally heavy snow. Freezing level could jump to 800 m.

Avalanche Summary

A couple small avalanches were observed in the Kootenay Pass area on Wednesday. One was a size 1 slab that was triggered on lower elevation (~1400 m) cut block. The slide was approximately 45 cm deep and may have released on a rain crust. The other event was a natural avalanche on a wind loaded slope immediately below ridge top.

Snowpack Summary

Recent winds have been redistributing the low density surface snow onto leeward slopes creating wind slabs that have been giving moderate compression tests results. Surface hoar buried at the end of November recently gave moderate to hard, but sudden results, in compression tests where it has been found as large as 10mm down 90-120cm, or shallower in the Rossland Range where it more of a concern. On a southwest aspect at 2020m in a shallow faceted snowpack area of Kootenay Pass, facets sitting on a rain crust recently gave moderate but resistant compression test results down 30-35cm. Recent reports suggest that the early November facet/crust deep persistent basal weakness has been producing inconsistent, but occasionally sudden snowpack test results and remains a concern. Keep this on your radar, especially when traveling in areas at higher elevations that have a smooth ground cover where the existing crust is uniform and consistent.

Problems

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.

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.