Avalanche Forecast

Issued: Feb 13th, 2015 8:21AM

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

pgoddard, Avalanche Canada

Purcells.

A Special Public Avalanche Warning is in effect for this region.

Summary

Confidence

Fair

Weather Forecast

Temperatures start cooling on Saturday with the passage of a cold front. 5-10 mm precipitation is expected overnight with the front Friday/ Saturday, tapering to flurries on Sunday. Freezing levels are around 2000 m on Saturday morning, falling towards 1500 m by the end of the day. Monday is dry and cool, with a chance of sun. Winds are light to moderate NW, easing to light by late Sunday.

Avalanche Summary

On Thursday, a size 2 natural avalanche was observed on a north-facing slope. Explosives also triggered numerous size 2-3.5 avalanches up to 2 m deep, some of which ran at ground. Large cornice falls were also observed. On Wednesday, a skier took a ride in a size 2 persistent slab which failed on the mid-Jan layer in the Dogtooth range. Explosives also triggered a size 3 slab which started with a cornice failure, then ripped out to ground. Explosives triggered a size 2.5 avalanche on the November crust/facet layer in an area that had previously slid and then reloaded. A very large natural slab was also observed just outside the region near Invermere (look for the blue pin on the bulletin regions map to get the full report). Clearly the snowpack is still capable of producing destructive avalanches, so tread carefully.

Snowpack Summary

More than a week of very warm temperatures has affected the snowpack by moistening upper snowpack layers to around 2000 m. Weve seen continued reactivity of persistent slabs as warming has altered the properties of the slab. Below treeline, the snowpack is probably trending isothermal (zero degrees throughout). In the alpine, wind affected surfaces can be found. Cornices may be large and weak.The late-Jan crust/surface hoar layer is 1-2 m deep in the west, and can be found within the upper metre of the snowpack further east. Its variably reactive. The mid-January surface hoar, deeper again, remains problematic in some areas. The mid-December weak layer may still be on the radar in isolated areas in the east. The mid-November weak layer of crusts and facets can still be found near the bottom of the snowpack. It seems to have reawakened with warming and has been triggered by explosives over the last few days, taking the entire snowpack with it. As temperatures cool this weekend, conditions should gradually improve, but its still a trouble-ridden snowpack adapting to change... so give it a bit of time.

Problems

Persistent Slabs

Persistent slabs are most likely to be triggered from thin snowpack areas, or with large triggers like cornice fall or an avalanche stepping down.

Avoid common trigger points like convexities or areas with a thin or variable snowpack.>Use conservative route selection; stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 5

Wind Slabs

Wind slabs may be lurking on lee and cross-loaded features in the alpine. Cornices are weak and may collapse.

Give cornices a wide berth when travelling on or below ridges.>Be cautious as you transition into wind affected terrain.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Loose Wet

Warm temperatures and drizzle have weakened the snowpack, especially at low elevations. Caution in areas receiving direct sun.

Be cautious of sluffing in steep terrain.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Feb 14th, 2015 2:00PM