Avalanche Forecast

Issued: Mar 20th, 2015 9:02AM

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

swerner, Avalanche Canada

Purcells.

Snow, rain and wind combined with buried weak layers makes the perfect recipe for avalanches. Check out the new forecasters blog @ avalanche.ca.

Summary

Confidence

Good

Weather Forecast

Is spring the new winter? Waves of light, convective precipitation will continue overnight Friday and into Saturday. Amounts up 3-10 mm on Saturday, ridgetop winds moderate from the SW and freezing levels 2100 m then falling to valley bottom overnight. A dry day with a mix of sun and cloud is forecast on Sunday as the Pacific ridge crosses the province. Monday will see somewhat cooler temperatures with freezing levels near 1800 m and light precipitation 3-8 mm. Unsettled conditions will continue and progress as a series of fronts and ridges move across the region next week.

Avalanche Summary

On Thursday a skier controlled size 1.0 slab avalanche was reported. However, the snow and wind didn't start up in the Purcell region until Thursday afternoon. I suspect some natural avalanche activity occurred on Friday. A concern still exists for avalanches to step down to deeply buried weak layers, especially in shallower snowpack areas. With new snow, rain and strong winds natural avalanche activity will likely continue through the weekend.

Snowpack Summary

At higher elevations, 10-30 cm snow sits over a plethora of old surfaces including wind affected surfaces, and/or old wind slabs and crusts which were buried mid-March. Previous strong winds have redistributed new snow into wind slabs on leeward terrain features and lower elevations (below 2000 m) are sporting spring-like, melt-freeze conditions. Digging deeper (20-50 cm below the surface) sits the mid-February facet/ crust interface. This interface has not been reactive in the Purcell's unlike regions to the North. However, it is alive and well in test profiles and may just require additional load and/ or a change in slab properties before it reaches threshold and becomes reactive. The late-Jan crust/surface hoar layer (around 1m deep) and the mid-January surface hoar (around 1.5m deep) have been dormant for several weeks.

Problems

Wind Slabs

Wind slabs found in lee terrain continue to be reactive to human triggering. The mid-February interface is buried 20-50 cm below the surface and seems to be stubborn. However; wind slabs failing on this layer will have larger destructive potential.

Use caution on lee slopes and terrain features. Recent storm snow has been redistributed forming touchy wind slabs.>Caution around convexities, whumphing and cracking are indicators of a buried weak layer. >

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

Steady rain and warming at lower elevations will saturate and weaken the upper snowpack.

Avoid exposure to terrain traps where the consequences of a small, wet avalanche could be serious.>Watch for clues, like natural avalanche activity, sluffing off of cliffs, and snowballing.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 3

Valid until: Mar 21st, 2015 2:00PM