Avalanche Forecast

Issued: Jan 31st, 2013 9:14AM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Wind Slabs and Persistent Slabs.

swerner, Avalanche Canada

Northwest Coastal.

Summary

Confidence

Fair

Weather Forecast

The next frontal system looks to be aimed at the North Coast for Friday bringing generally light precipitation amounts and rising freezing levels. The brunt of the frontal system will take affect through the weekend with temperatures dropping Sunday night.Friday: Light precipitation, snow amounts 5-8 cm above 1000 m. Ridgetop winds light from the SW and moderate SW for areas north of the Portland Inlet. Alpine temperatures -3.0 and freezing levels near 900 m. Saturday: No significant precipitation expected. Cloudy skies with ridgetop winds moderate from the South. Alpine temperatures -1.0 and freezing levels rising to 1300 m. Saturday night into Sunday: The next wave of precipitation bringing light-moderate amounts. Ridgetop winds moderate from the south. Alpine temperatures dropping to -4.0 and freezing levels near 800 m in the afternoon falling to valley bottom overnight.

Avalanche Summary

Natural avalanche activity up to size 2.0 was reported from a NE aspect around 1200 m, suspect cornice fall pulling out the slab on the slope below. Isolated small slabs up to size 1.5 initiated from steep alpine features.Avalanche control work using explosives produced numerous slab avalanches up to size 3.0 in the Northern parts of the region. These ran on NE-S aspects 1300 m and above. Failure planes were ground and within recent storm snow, all on previously controlled slopes.

Snowpack Summary

Wind slabs are most likely found on SE-W aspects, behind terrain features like ridges and ribs, and may be easily triggered under the weight of a person. Warmer temperatures have promoted some settlement and consolidated the recent storm snow into slab-like characteristics. Surface snow may become moist or wet at treeline and below and become unstable.Lingering beneath the new snow sits a persistent weaknesses comprising of surface hoar/ facets/ crust. Recent test done on these layers are producing hard results with sudden and resistant planar results. I suggest you keep these on your radar in regards to reactivity and sensitivity until we get through the warming period. If reactive, these layers could produce large avalanches. The mid and lower snowpack is generally well settled and strong, although basal facets remain a concern in the northern part of the region.

Problems

Wind Slabs

Strong shifting winds have built touchy wind slabs that are likely found behind terrain breaks such as ridges and ribs and on lee slopes. Wind slabs may be easily triggered under the weight of a person and/or a machine.

Avoid freshly wind loaded features.>Avoid lee and cross-loaded terrain near ridge crests.>Use ridges or ribs to avoid pockets of wind loaded snow.>

Aspects: North, North East, East, South East.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 5

Persistent Slabs

Over the past week up to meter of new snow has fallen on a crust/facet/surface hoar interface. This interface may be found most reactive in sheltered areas over convex rolls or steep terrain. Dig down and see how reactive it is in your riding area.

Whumpfing is direct evidence of a buried instability.>Dig down to find and test weak layers before dropping into your run or line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Feb 1st, 2013 2:00PM