Avalanche Forecast

Issued: Apr 10th, 2014 9:34AM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs and Deep Persistent Slabs.

ghelgeson, Avalanche Canada

Purcells.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain on Sunday

Weather Forecast

Synopsis: High pressure at the surface and aloft should result in a classic spring pattern. Freezing levels are expected to rise above treeline each day, dropping almost to valley bottom overnight. Winds should back way off, only light values are expected even at ridgetop through the weekend.Friday: Freezing Level: 1500m rising to 2000m; Precipitation: 0:2mm - 1:3cm; Wind: Treeline: Light, SW | Ridgetop: Moderate, W/NWSaturday: Freezing Level: Valley Bottom rising to 1700m; Precipitation: 0:2mm - 1:3cm; Wind: Treeline: Light, NE | Ridgetop: Light, NWSunday: Freezing Level: Valley Bottom rising to 2000m; Precipitation: Nil; Wind: Treeline: Light, N | Ridgetop: Light, NW

Avalanche Summary

Lots of loose wet activity to size 2 on all aspects between 1700 and 1900m Wednesday. Some natural wind slabs ran naturally to size 2 on NE and E facing features at 2500m too.

Snowpack Summary

Warm temperatures resulted in the freezing level reaching to almost 2400m early this week in the southern Purcells, around 1800m in the north. This has helped to settle out last weeks storm snow, it's reported to be bonding well to the old surface. Strong winds out of both the SW and NW have redistributed what little dry snow still exists at upper treeline and alpine elevations into wind slabs that are most prevalent immediately lee of ridge crest Three persistent weak layers exist in the highly variable snowpack of the Purcells:The mid-March sun crust/surface hoar layer down 50-80cm still has potential for human-triggering in isolated areas. The early-March crust/facet/surface hoar layer down around 80-120cm has become less susceptible to human triggering, but still has the capacity to produce large avalanches.The mid-February crust/facet/surface hoar combo is typically down 60 - 120cm. Direct triggering of this layer has become unlikely, however, cornice fall, a smaller avalanche in motion or prolonged warming may wake this layer up, which would result in very large and destructive avalanches.Weak basal facets exist in many areas, but triggering is unlikely.

Problems

Wind Slabs

Wind slabs immediately lee of ridge crest and mid slope features may still be sensitive to human triggering. Keep an eye on overhead cornices too, you don't want to be underneath or on top of one when it releases.

Give cornices a wide berth when travelling on or below ridges.>Be careful with wind loaded pockets, especially near ridge crests and roll-overs.>Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>Assess start zones carefully and use safe travel techniques.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 3

Deep Persistent Slabs

A bomber spring snowpack is still a few weeks away. For now, the potential for very large deep slab avalanches needs to remain on your radar. Cornice fall, strong solar, warming temps or a surface avalanche in motion could wake the sleeping giant.

Carefully evaluate big terrain features by digging and testing on adjacent, safe slopes.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Be aware of the potential for very large, deep and destructive avalanches due to the presence of deeply buried persistent weak layers.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Unlikely - Possible

Expected Size

4 - 8

Valid until: Apr 11th, 2014 2:00PM