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Avalanche Forecast

Archived

Jan 14th, 2013–Jan 15th, 2013

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

Regions

Kootenay Boundary.

I’ve based this forecast on a weather model that shows rapidly increasing alpine temperatures on Tuesday. If it doesn’t warm up, then these danger ratings are one notch too high.  See the forecasters blog for warming details.

Confidence

Poor - Freezing levels are uncertain for the entire period

Weather Forecast

Tuesday: Winds out of the NW at extreme values. Freezing level rising to 2300m+ around lunch time.  No snow/rain. Clearing skies.Wednesday: Freezing level stays high around 2300m.  Strong NW winds persist.  No precip expected.Thursday: Freezing level comes down to 2000m.  Winds switch to westerly strong.  Increasing to westerly extreme in the afternoon.

Avalanche Summary

Skiers are still triggering some sluffing in steep terrain.  A small slab popped out Saturday night and there was also a report of a skier controlled size 1 failing on facets 20 cm below the snow surface. Avalanche activity is fairly benign at the moment.

Snowpack Summary

Winds picked up out of the west Sunday creating a thin wind slab 5 - 15cm thick in open alpine and treeline features.Under this new wind slab 65 cm of settled snow rests on the January 4th interface which consists of small facets, surface hoar (up to 12mm) in sheltered treeline and below treeline areas and sun crust on steep south and west facing slopes. The bonds at this interface are improving.? The layer is still alive and well in test pits but has not been reactive to human triggering in the last day or so.? Wind slabs created by the previously raucous SW winds have grown old & tired. The midpack is well bonded and strong. The November 28 surface hoar is still being found in isolated, sheltered below treeline locations buried 120cm. The deep crust/facet combo from early November still exists but seams to have gone dormant for the time being.

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.