Avalanche Forecast

Issued: Feb 21st, 2018 4:24PM

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 reactive wind slabs and cornices in open areas. 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 up to 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, northwest. Temperature -8. Freezing level valley bottom.

Avalanche Summary

Tuesday numerous skier triggered storm and wind slab avalanches up to size 1.5 were reported. Most of these failed on the mid-February interface which was especially reactive on solar aspects where a suncrust was buried.On Monday, several natural wind slab avalanches to size 3 were reported on a wide range of aspects above 2100m. On Sunday we received reports of several wind slab avalanches to size 2, on a wide range of aspects. See here for a good example in the MIN report. On Saturday explosives control work produced several storm slab avalanches to size 2.5 on a wide variety of aspects near tree line. 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 has settled into a slab in the upper snowpack. Strong winds, most recently from the north / east, redistributed these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie the old interface that 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 150-200 cm of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or the other of these on all aspects and elevations.Deeper in the snowpack 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
Watch for wind slab development on south through west aspects due to 'reverse loading' from previously strong winds blowing from the north. These have been particularly reactive where they overlie a buried suncrust.
Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

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 from shallow or thin. rocky snowpack 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