Avalanche Forecast

Archived

Jan 6th, 2012–Jan 7th, 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 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.

Regions

Cariboos.

Confidence

Fair - Freezing levels are uncertain on Sunday

Weather Forecast

Flurries during the day on Friday should accumulate a couple of new cm by Saturday morning. A weak ridge of high pressure building over the coast is forecast to develop strong winds from the west or northwest and warm temperatures in the Cariboo. Moderate precipitation is expected to begin by midnight and continue during the day on Sunday. The freezing level is expected to rise to about 1800 metres in the Cariboo and West Monashee by Sunday morning. It looks like most of the snow will fall in the North and West of the Interior ranges. Expect moderate to strong northwest winds on Sunday becoming strong from the west in the South Columbia and Purcells. Cooler air is expected to move in to the region from the northwest on Monday. Precipitation amounts are un-certain at this time. Chinook conditions are expected for the Rockies.

Avalanche Summary

No new reports from this region. I suspect that the poor visibility and travel conditions have limited observers ability to report. Explosives testing to the south of this region has produced very large avalanches releasing in the mid-december surface hoar layer.

Snowpack Summary

Another 10-15 cm of new snow overnight arrived with cooler temperatures. The recent snowfalls add up to about 50-70 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. The height of snow in the region is between 200 cm in the drier areas and close to 300 cm in the wetter areas. The storm has been very mild, with freezing levels near 1800 metres on Wednesday. The temperatures started to fall early Thursday morning when the rain and snow moved out of the region. The winds have been very strong from the south and southwest. Expect to find windslabs on north and northeast aspects in the alpine and at treeline. There may be a rain crust developing below 1600 metres as the freezing levels drop back to valley bottom. The previous storm snow is now fairly well consolidated and makes for a generally strong mid-pack. A surface hoar layer buried around Christmas is well preserved, now buried around 80 cm below the surface and is producing sudden "pop" results in stability tests. A surface hoar/facet/crust interface from mid-December is buried 100 to 150 cm deep and is still reactive to natural and human triggers.

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.