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Avalanche Forecast

Archived

Mar 8th, 2012–Mar 9th, 2012

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

Regions

South Rockies.

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Another dry day is expected for Friday. Freezing level is expected to remain high at around 2300 m and strong southwesterly winds are anticipated. For Saturday, flurries or light rain is expected, with only minimal accumulation. Winds should be moderate southwesterly and freezing levels should drop to around 1800 m. On Sunday, further light snow/rain is expected with continued southwesterly winds and freezing levels around 1700 m.

Avalanche Summary

On Wednesday, a size 2 avalanche was reported from around 2300m in the South York Creek area on an east aspect. Limited amounts of sluffing from solar activity was also noted. On Tuesday a snowmobiler was buried in an avalanche below treeline in the Flathead: more details are here: https://avalanche.ca/Forums/forums/t/5550.aspx

Snowpack Summary

20 to 50 cm of recent storm snow has been reported from different parts of this region. Winds from the SW and the NW have set up wind slabs in lee areas in exposed terrain. Warm temperatures have moistened the snow surface in many locations; where this has happened, expect an overnight freeze to set up a surface crust. The mid February surface hoar layer is now down between 40 & 100cm and is more prevalent in the west and south of the region, particularly in the Flathead. Recent snowpack tests as well as a rider-triggered avalanche on this weak layer indicate that it still has the potential to be triggered in many areas and if it is triggered, a large avalanche could result. Lingering concern remains for basal facets, particularly in shallower snowpack areas with steep, rocky start zones. Cornices are becoming well developed in response to recent winds and are likely starting to droop with the warm temperatures.

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.

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.

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.