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Avalanche Forecast

Archived

Dec 26th, 2011–Dec 27th, 2011

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Kootenay Boundary.

We are receiving very few field observations from this region. You can help! Tell us what you are seeing out there: email [email protected]

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

Tuesday: Light snow. Strong westerly winds. Freezing level near 1000m.Wednesday: 20-25cm snow. Moderate-strong west to south-west winds. Freezing level around 1450m.Thursday: 10-15cm snow. Moderate to strong west to south-west winds. Freezing level 1400m, lowering in the afternoon.We are in a challenging period for weather forecasting. Check out the Forecaster's Blog for more information on this and how it affects the avalanche forecasts.

Avalanche Summary

A natural and skier-triggered avalanche cycle with slabs up to size 2 was observed over the last couple of days. These were failing on the mid-December surface hoar on north through east aspects from 1700m to the peaks. Wind loading from the south-west overnight Sunday led to naturally-triggered wind-slabs on lee slopes on Monday morning. Touchy conditions are likely to continue through the forecast period.

Snowpack Summary

Up to 20cm of new snow has been redistributed by south-west winds into touchy wind-slabs on lee slopes. A buried surface hoar layer from mid-December around 30cm down is now highly reactive. It is well-preserved with 10-15mm crystals and is most reactive well below ridges in protected terrain. The mid-pack is generally well settled. Facets exist at the base of the snowpack.

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.