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Avalanche Forecast

Archived

Dec 31st, 2011–Jan 1st, 2012

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

Regions

South Rockies.

Confidence

Fair - Forecast snowfall amounts are uncertain on Tuesday

Weather Forecast

The weak ridge that brought cooler and drier conditions on Saturday is expected to be pushed out of the region by Sunday morning. Warm moist air should bring cloud and rising freezing levels to about 1000 metres on Sunday. The winds are expected to build from the southwest on Monday, and moderate precipitation should start to accumulate snow by late afternoon. A trailing cold front is forecast for Tuesday. Snowfall amounts are un-certain and will depend on how much moisture is in the area when the cooler air arrives.

Avalanche Summary

Skiers remotely triggered a size 2.0 slide from 10 metres away, that was 60 cm deep, 70 metres wide, and 75 metres in length. Natural avalanche activity reported today was limited to a natural wind slab release size 2.5 from an North-East aspect. We continue to get reports of old activity that occurred during the recent storm.

Snowpack Summary

Tests in Hartly Creek today showed easy results down 20 cm on a layer of stellar crystals. Height of snow in the Koko Claims area is 120 cm at 200 metres. The mid-december surface hoar is down about 30 cm. The mid-pack is generally well consolidated, and there is a 20 cm layer of 4F facets and depth hoar at the ground. The surface hoar is producing easy to moderate shear test results.

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.