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Avalanche Forecast

Archived

Dec 4th, 2012–Dec 5th, 2012

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

Regions

South Rockies.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Overnight and Wednesday: Light to locally moderate snowfall overnight, easing off by Wednesday morning / Strong to extreme southwest winds / Freezing level at 1600m overnight dropping to surface by Wednesday morning Thursday: Light snowfall / Moderate west winds / Freezing level at 900mFriday: Possibility of clearing / Light southwest winds / Freezing level at surface

Avalanche Summary

Several size 1-1.5 soft slabs were ski cut in the Westcastle area on Monday. They occurred with the recent storm snow on north to northeast facing terrain between 1900 and 2200m.

Snowpack Summary

Recent storm accumulations have been highly variable throughout the region with some reports from the east side of the region indicating storm slabs up to 40cm deep. Warmer temperatures at lower elevations have created moist surfaces that will most likely form a temperature crust with dropping freezing levels. Ongoing light to locally moderate snowfall and strong to extreme winds will create pockets of windslab at treeline and above.The November crust was found to be buried down about 60 cms and was associated with a layer of facets either directly above or below. In general, snowpack data is sparse in this region and significant variations likely exist from one drainage to another. Digging down and making your own observations will be critical to safe slope selection. Any observations from the field are welcome at [email protected].

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.