Avalanche Forecast

Issued: Feb 21st, 2018 4:19PM

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

Avalanche Canada jmcbride, Avalanche Canada

Previous strong winds have formed wind slabs in wind-exposed areas, and have been reactive to human triggers.  Keep in mind that large avalanches on buried weak layers may still be 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 cm. Ridge wind light, southwest. Temperature -12. Freezing level valley bottom.SATURDAY: Mix of sun and cloud, light flurries. Accumulation trace. Ridge wind light, west. Temperature -10. Freezing level valley bottom.

Avalanche Summary

Tuesday there were several reports of skier triggered wind slab avalanches up to size 1.5 on a variety of aspects between 1800-2100 m, including a remotely triggered (from a distance) pocket of hard wind slab near ridge top. On Monday, several natural wind slab avalanches to size 2.5 were reported on a south / west through north / west aspects between 1800m and 2400m.On Sunday, natural wind slab activity was widespread above 1900m on primarily south east through west aspects. We received reports of an initial wind slab (size 2) stepping down to deeper weak layers and triggering a size 3.5 persistent slab, on a south west aspect near 2300m. Also on Sunday, skiers were able to trigger small storm slabs low down on MacPherson on the widespread rain crust that formed February 8th. See the MIN report for more details. 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

40-60 cm of recent storm snow is settling into a slab in the upper snowpack. Strong winds, most recently from the north, have redistributed these accumulations into deeper, reactive slabs in wind-exposed terrain. The recent snow sits on the old interface the was buried mid February consisting of; a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, a rain crust below 1600m, and surface hoar on sheltered slopes.Below the snow surface, several persistent weak layers make up a complex snowpack which is slowly beginning to show signs of improving but still remains suspect. In the top 1.5-2.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.Deeper in the snowpack (around 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

An icon showing Wind Slabs
Reactive wind slabs as a result of previously strong winds can be found in open areas at lower elevations as well as in the alpine.
Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered, 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

An icon showing Persistent Slabs
Buried weak layers exist in the snowpack and may be reactive to large triggers such as a cornice or step-down from a 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

Unlikely - Possible

Expected Size

2 - 4

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