Avalanche Forecast

Issued: Feb 15th, 2018 3:39PM

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.

shorton, Avalanche Canada

Kootenay Boundary.

Two incoming storms will elevate the danger. Continue to choose conservative terrain and limit your exposure during the storms.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

FRIDAY: Flurries throughout the day with 5-15 cm of new snow and then clearing in the evening, moderate to strong west wind, alpine high temperatures around -6 C.SATURDAY: Another storm pulse brings 20-30 cm of new snow throughout the day, moderate southwest wind, alpine high temperatures around -4 C.SUNDAY: Lingering flurries with light east wind and alpine high temperatures around -15 C.

Avalanche Summary

Wednesday's storm produced a few small (size 1) skier-triggered slabs on north facing terrain at treeline elevations, while explosive control produced a few size 2 avalanches in wind-affected terrain.Last weekend, three large persistent slab avalanches (size 3) were reported on northeast aspects in the Valhallas. Two were triggered with explosive and the third was naturally triggered. These were large avalanches with fracture depths of over a metre. Natural activity on deeply buried weak layers has wound down recently, but human triggering remains a real concern.Expect the incoming snow to form reactive slabs as well as potentially stress deeper weak layers.

Snowpack Summary

Fresh slabs will grow with the incoming storms. A few interfaces buried 20-30 cm below the most recent snow could potentially support wide propagations in the fresh storm/wind slabs. This includes sun crusts on steep south-facing slopes, a rain crust below 1800 m, small surface hoar in isolated areas, and hard wind slabs at upper elevations. Fragile cornices may be found at ridgetop. We now have 1-2 m of settled snow sitting on three significant surface hoar/crust layers that were formed early to mid-January, and back in December. Near the base of the snowpack a crust/facet interface exists that will likely haunt us all season. These persistent weak layers that lurk within the snowpack have produced large and destructive avalanches. Although this activity has been diminishing gradually, recent activity and continued sudden snowpack test results have kept them a top concern in the region.The complex and widespread nature of our multiple overlapping persistent slab problems continues to demand respect and diligence from backcountry travelers in the region.

Problems

Wind Slabs

Wind slabs will continue to grow on Friday with strong west wind and 5-15 cm of new snow. Beware of an interface buried up to 30 cm below the surface that could support wide propagations.

Choose well supported terrain without convexities.Use caution in lee areas in the alpine and treeline. Storm snow will form slabs.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 - 2

Persistent Slabs

Several deeply buried weak layers exist in the snowpack. Although the likelihood of triggering a persistent slab is gradually decreasing, the consequences remain very high.

Avoid steep convexities or areas with a thin or variable snowpack.Minimize exposure during periods of heavy loading from new snow and wind.Pay attention to overhead hazards like cornices which could trigger persistent slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2.5 - 4

Valid until: Feb 16th, 2018 2:00PM