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Avalanche Forecast

Archived

Jan 31st, 2013–Feb 1st, 2013

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

Regions

Purcells.

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Saturday

Weather Forecast

Overnight and Friday: 2-3 cms expected tonight combined with strong Northwest winds and alpine temperatures about -8.0. Snow ending by morning, becoming high overcast with freezing level rising to about 1300 metres and light Northwest winds.Saturday: Mostly sunny with light West winds. Above freezing temperatures are expected in the alpine up to about 2300 metres.Sunday: The next Pacific disturbance is expected to move into the interior from the coast. Temperatures should drop below freezing at all elevations before the system arrives.

Avalanche Summary

Natural and skier controlled avalanches were reported  up to size 2.0 on North thru East aspects in the alpine and at treeline. Loose snow sluffing in steep terrain continues to be reported up to size 1.0.

Snowpack Summary

Westerly winds and warm temperatures overnight have continued to develop wind slabs in the alpine and at treeline. Wind slab was reported to be stiffening from fist to four finger hardness. The recent storm slab has been settling and becoming more cohesive. Pockets of slab that were mostly between 30-50 cms deep above the January 23rd weak layer have started to release naturally or when light additional loads have been added (like ski-cutting). As we head into a warming period expect the recent storm slab to become more reactive. The forecast warm temperatures at higher elevations on Saturday may help initiate releases on the January 23rd layer. The deeper weak layer from January 4th is reported to be gaining strength, and I don't expect that we will see releases on this layer from one day of solar radiation and warm temperatures. That being said, if cornices start to fall off from the heating on Saturday, that might be enough of a load to trigger the deeper January 4th layer.

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.