Avalanche Forecast

Issued: Feb 5th, 2013 9:36AM

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

Cariboos.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Wednesday: Today the region sits under a weakening zonal flow maintaining moderate-strong ridgetop winds from the West. An upper disturbance embedded in the flow will bring snow amounts up to10 cm. Treeline temperatures steady -4 and freezing levels steady around 900 m. Thursday: Unsettled conditions continue, bringing light snow accumulations. Ridgetop winds will switch and blow from the SW. Treeline temperatures near -3 and freezing levels hovering around 1200 m, falling to valley bottom overnight.Friday: Outlook shows surface and upper ridge building, bringing dryer conditions and valley cloud. Treeline temperatures near -8 with freezing levels hovering around 900 m. Ridgetop winds blowing moderate from the NW.

Avalanche Summary

Over the past couple of days a widespread natural avalanche cycle occurred up to size 2.5 mostly on NE-E aspects above 2000 m. A large natural size 3 slab avalanche was also reported from a large uneven south facing slope. the suspected failure plane being the buried crust down 40-80 cm. Several skier triggered avalanches up to size 2 were initiated from a variety of aspects and elevations ranging from 155-2200 m.

Snowpack Summary

The old storm snow has settled into a dense slab that can be triggered by skiers or sledders and produce avalanches up to size 2.0. There has been a lot of wind transport and wind slab formation in the alpine. Forecast new snow and strong SW winds will build fresh wind slabs and add to the recent storm slab which sits on a spotty and variable weak interface buriedÂ 40-80 cm down. Professionals are finding the early January surface hoar layer to be well preserved in more locations below 2000 metres than had been suspected. Use extra caution on solar slopes due to a buried crust interface and open slopes, cutblocks and convex rolls at and below treeline where buried surface hoar may be preserved.

Problems

Wind Slabs

Old wind slabs continue to be a concern, and new wind slabs are will build with the next pulse of moisture. Concerning areas are on lee slopes and behind terrain features like ridges and ribs, and could be triggered under the weight of a person.

Avoid freshly wind loaded features.>Whumpfing, shooting cracks and recent avalanches are all strong indicators of an unstable snowpack.>Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 4

Persistent Slabs

50-70 cm slab is sitting on a variety of old surfaces that were left after the dry period of mid-January. These layers comprise of buried crusts on solar aspects and surface hoar in sheltered polar aspects.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Dig down to find and test weak layers before dropping into your line.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Feb 6th, 2013 2:00PM