Avalanche Forecast

Archived

Jan 7th, 2012–Jan 8th, 2012

Alpine

Natural and human triggered avalanches likely.

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 unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Cariboos.

Confidence

Fair - Forecast snowfall amounts are uncertain on Sunday

Weather Forecast

The Pacific system that hit the north coast today is moving inland this evening. Very strong winds on the coast are expected to diminish to about 70 km/hr from the southwest by the time they reach the Cariboos and the Monashees. I expect that there will be about 15-20 cm of new snow by Sunday morning. The freezing level is forecast to rise to about 1500 metres on Sunday morning, and then lower back to 1000 metres by Sunday evening. Another pulse of snow is forecast for Sunday evening that looks like it will bring another 10-15 cm combined with moderate southwest winds. The snow should end during the day on Monday after leaving about 5cm. Cooler clear weather is expected Monday night and should continue for Tuesday.

Avalanche Summary

A natural cornice failure from Friday on an east aspect at 2600 metres caused an avalanche size 2.5

Snowpack Summary

Strong southwest winds and moderate to heavy precipitation has begun to build new windslabs in the alpine and at treeline. The recent snowfalls add up to about 60-80 cm of "storm" snow that has been available for wind transport. The warm temperatures and high freezing levels caused the wind transported snow to become a well consolidated slab. There are two rain crusts below 1550 metres. The rain crusts are variable, but they are giving planar results in tests. At treeline the storm snow is reported to be giving sudden planar results down 40 cm, and the surface hoar/crust layer that is down 80cm is also giving sudden planar results. This tells me that the new load of snow that we are expecting may activate these weak layers. The mid-pack is reported to be strong, and I have not heard anyone talk about early season layers deep in the snowpack.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.