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Avalanche Forecast

Archived

Jan 9th, 2012–Jan 10th, 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 unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

Kootenay Boundary.

Confidence

Good - -1

Weather Forecast

A weakening cold front associated with the big weekend storm slides across the region Monday night persisting into Tuesday. The Kootenay Boundary region will receive light precipitation out of the system; I'm not expecting more than 5 cm by the end of the day Tuesday. A ridge of high pressure builds in Tuesday afternoon bringing dry conditions and lowering freezing levels down to valley bottom by Tuesday evening. Moderate to strong winds will be blowing out of the NW Tuesday in exposed locations. Expect a daytime high of -5 with an overnight low of -9 @ 1500m. Wednesday looks to be cool and dry with no precipitation expected.

Avalanche Summary

A size 1.5 skier accidental was reported Sunday from a thin snowpack zone where the total HS is around 100 cm. The skier triggered the avalanche on the mid December surface hoar (SH) layer. The SH was up to 15mm in size & very well preserved. All other observations were limited to sluffing in steep terrain.

Snowpack Summary

Previously gusty winds created wind slabs that can be found in wind exposed locations in both the treeline & alpine elevation bands. A thin melt/freeze crust can be found as high as 1900m & is now buried a few cm's below the surface. Compression tests have been producing sudden results on both the late December surface hoar down 35-50 cm & the mid-December surface hoar, down 70-105 cm. Test profiles and continued whoomphing suggest that avalanches associated with these persistent weakness's have the potential to propagate over large areas. Basal facets and depth hoar remain a concern in shallow rocky areas.

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.