Avalanche Forecast

Issued: Feb 7th, 2013 9:58AM

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

swerner, Avalanche Canada

Cariboos.

Weak layers within the upper snowpack have yet to be tested by the effects of the sun. Blue skies and fresh snow may tempt you into steeper and bigger terrain. Maintain a diligent approach to terrain selection to best manage the current conditions.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain for the entire period

Weather Forecast

Friday: A weakening upper trough moves out of the region as a ridge of high pressure makes its way in. The initial changes in the weather pattern will bring only trace amounts of new snow and broken cloud. Periods of sunshine and solar radiation may exist. Ridgetop winds will be light-moderate from the NW. Treeline temperatures will be near -5 and freezing levels around 900 m. Saturday: The ridge of high pressure builds and brings dry conditions with periods of scattered to few clouds allowing some sunny alpine skies. Ridgetop winds will blow light-moderate from the NW. Treeline temperatures near -2 and freezing levels rising to 1300 m then dropping to valley bottom overnight.Sunday: The upper ridge strengthens with continued dryer conditions. Ridgetop winds light from the NW. Treeline temperatures near -5 and freezing levels around 1100 m.

Avalanche Summary

Some natural avalanche activity occurred on Wednesday. One loose dry avalanche size 2.5 initiated from steep East facing terrain above 2000 m and a skier triggered size 1 slab avalanche from a NW aspect around 1900 m. Earlier this week a large natural size 3 slab avalanche was reported from a large uneven south facing slope, the suspected failure plane being the buried crust down 40-80 cm. Heads up out there! I suspect avalanche activity to continue through the forecast period, additional concerns being periods of solar radiation as a natural trigger.

Snowpack Summary

20-40 cm of new snow sits on wind slabs and recently buried surface hoar, sun crusts and facets that formed at the beginning of February. Old storm snow has settled into a dense slab that could be triggered by skiers or sledders and produce avalanches up to size 2.0. This slab sits on a persistent weak interface deeper (40-80 cm down) in the snowpack, comprising yet again of crusts, surface hoar and facets that were buried January 23rd. Use extra caution on large open slopes, cutblocks and convex rolls at and below treeline where buried surface hoar may be preserved. Wind slabs continue to develop and stiffen on lee slopes (N-SE) and behind terrain features like ridgelines and ribs.The midpack is generally well settled and strong. Average snowpack depth at treeline elevations is near 200 cm.

Problems

Persistent Slabs

New storm snow adds to the depth (50-80 cm) of the slab that is sitting on a variety of old surfaces comprising of surface hoar, crusts and facets. Persistent slabs continue to be reactive to rider triggers and can be difficult to predict.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Whumpfing is direct evidence of a buried instability.>Good group management is essential to manage current conditions safely.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 5

Wind Slabs

Old wind slabs continue to be a concern, and new wind slabs have formed. Concerning areas are on lee slopes and behind terrain features like ridges and ribs. They could be triggered under the weight of a person. Cornices may threaten slopes below.

Avoid freshly wind loaded features.>Use ridges or ribs to avoid pockets of wind loaded snow.>Stay off recent wind loaded areas until the slope has had a chance to stabilize.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 5

Valid until: Feb 8th, 2013 2:00PM