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Avalanche Forecast

Archived

Jan 29th, 2012–Jan 30th, 2012

Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
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, human triggered possible.

Regions

Cariboos.

Confidence

Fair - Timing, track, or intensity of incoming weather is uncertain

Weather Forecast

After the storm clears a westerly zonal flow pattern with short lived disturbances is expected for Monday & Tuesday. That means westerly (upslope) regions should see the bulk of the precipitation (around 10 - 20 cm daily in favoured areas), moderate SW winds, and freezing levels around 1000 m on Monday and a little higher (warmer) on Tuesday. Wednesday the pattern is set to change as a ridge builds and dries out the area with warming temperatures. Thursday freezing level is expected to be around treeline (2000mis possible).

Avalanche Summary

Few avalanches reported Saturday; limited visibility restricted observations. Professionals working in the area expect today (Sunday) to have a widespread natural avalanche cycle including large full-path avalanches running from alpine to valley bottom, large windslabs at treeline and alpine elevations (to around size 2.5), widespread storm snow avalanches (independent of wind-loading) at all elevations, and possibly even deep releases at treeline and below treeline elevations on the deeply buried facet & crust combination. Looking forward to Monday I expect natural activity will taper off but will not have fully stopped and conditions will remain primed for human-triggered slides, which could be large. I would continue to remain very suspicous of cornices and the possibility of cornice triggered slides.

Snowpack Summary

Around 40 to 60 cm of new snow in the past 24 hours and storm snow totals of 150 cm or more are reported. Mod southerly or southwesterly winds have created windslabs and large fragile cornices. Warm temperatures are promoting storm slabs in the short term (upside down storm snow layers) and settling (strengthening) in the slightly longer term. All this new snow increases the load (stress) on deeper layers created during the mid-January cold snap; namely facets (sugar) and a crust at lower elevations (say 1500m and lower). This layer is now deeply buried (around 200 cm or more in many places) but snowpack test results on this layer range from no result to easy (variable strength) but the shear pops (if triggered it wants to propagate).

Problems

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.

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.