Avalanche Forecast

Issued: Feb 21st, 2018 4:15PM

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

jmcbride, Avalanche Canada

Cariboos.

Previous strong winds have formed reactive wind slabs in open areas and cornices at ridge crest. Keep in mind that large avalanches on buried weak layers are still possible and choose terrain carefully.

Summary

Confidence

Moderate -

Weather Forecast

THURSDAY: Mix of sun and cloud. Ridge wind light, northeast. Temperature -12. Freezing level valley bottom.FRIDAY: Flurries. Accumulation 5-10 cm. Ridge wind moderate to strong, southwest. Temperature -10. Freezing level valley bottom.SATURDAY: Cloudy, light flurries. Accumulation up to 5 cm. Ridge wind moderate, west. Temperature -9. Freezing level valley bottom.

Avalanche Summary

Tuesday there was a report of a skier triggered size 1.5 soft, wind slab release on a northwest-facing open, treeline slope at 1900 m.On Sunday, natural wind slab activity to size 3 was reported on south / east aspects from 1250m right up to 2400m elevation. See this MIN post for a good example of these avalanches. See also this MIN post for dramatic photos of wind effect. On Saturday we received reports of a large avalanche running on a deeply buried weak layer with 1.5m crown and good propagation. This feature was steep open terrain below tree line on an east facing aspect. Although deeper, persistent avalanche activity has become less frequent over the past week, light triggers in shallow rocky areas, as well as large triggers such as a cornice collapse or step down from a wind slab release, still have the potential to result in large destructive avalanches.

Snowpack Summary

25-40cm of storm snow from last week is settling into a slab in the upper snowpack. Winds have been strong from the north west through south west, creating reactive hard wind slabs (10-15 cm thick) in exposed locations on down wind features. See here for a good video summarizing conditions near Valemount. These accumulations overlie the old interface that was buried mid-February and consists of; a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, and surface hoar on sheltered slopes.Below the snow surface, several persistent weak layers make up a complex snowpack that still remains suspect. In the top 1-1.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find at least one of these layers on all aspects and elevations.Deeper in the snowpack (120-200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below tree line.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.

Problems

Wind Slabs

Wind slabs have formed as a result of previously strong, northerly winds and can be found in open areas at lower elevations as well as in the alpine. These slabs vary from soft to hard but have been reactive to human triggers.

Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2.5

Persistent Slabs

Buried weak layers exist in the snowpack and may be reactive to large triggers such as a cornice or wind slab release. Human triggering may also be possible in shallow or thin, rocky areas.

Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 22nd, 2018 2:00PM