Avalanche Forecast

Issued: Feb 14th, 2018 4:11PM

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

shorton, Avalanche Canada

Kootenay Boundary.

The low probability but high consequence of triggering a large persistent slab avalanche warrants conservative terrain selection, like sticking to small terrain features and avoiding wind loaded slopes.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Friday

Weather Forecast

THURSDAY: Mix of sun and cloud, light to moderate northwest wind, alpine high temperatures around -12 C.FRIDAY: Flurries throughout the day with about 10-15 cm of new snow and then clearing in the evening, moderate to strong northwest wind, alpine high temperatures around -8 C.SATURDAY: Another storm pulse brings 10-15 cm of new snow, strong west wind, alpine high temperatures around -10 C.

Avalanche Summary

Preliminary reports from Wednesday suggest the latest storm snow is reactive. Some some small natural storm slab activity was reported in north-facing wind affected terrain, while explosive control and ski cutting produced some size 1-2 slabs.Prior to the most recent storm, several skier-triggered wind slabs were reported. They were mostly small slabs (size 1) on north and west facing slopes at treeline. 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.

Snowpack Summary

15-30 cm of fresh snow has formed thin reactive slabs. The snow sits above a hard crust below 1800 m and on steep south-facing slopes. In alpine terrain, the new snow has buried older wind slabs that may still be reactive in isolated areas. 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

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.Avoid slopes when the solar radiation is strong, especially if they have large cornices overhead.Manage overhead hazards carefully and avoid lingering in runout zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

2.5 - 4

Storm Slabs

Fresh storm slabs have formed over a variety of old surfaces, including hard crusts. Storm slabs are most likely on steep features at higher elevations and where the wind has formed thicker slabs.

Use ridges or ribs to avoid pockets of wind loaded snow.Use caution in lee areas in the alpine and treeline. Storm snow will form slabs.Choose well supported terrain without convexities.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Valid until: Feb 15th, 2018 2:00PM