Avalanche Forecast

Issued: Apr 19th, 2015 8:11AM

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

pgoddard, Avalanche Canada

Purcells.

Danger ratings reflect conditions during the hottest parts of the day. Time your travel to take advantage of cool temperatures. Danger ratings end today, but check back for spring and summer advice.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

Monday should bring warm, dry weather with light winds. The freezing level climbs to 2600 m.

Avalanche Summary

On Friday, a helicopter remotely triggered a small slab on a wind loaded feature. It failed on the buried April weak layer. A skier remotely triggered a size 1 avalanche on a high north aspect on Thursday. It failed on facets down 20 cm. A naturally-triggered size 2 slab was also observed. Explosives have triggered several size 2 cornice falls over the last few days. On Wednesday, natural solar-triggered avalanches to size 2 were reported. Explosives triggered several slab avalanches and a skier triggered a size 1.5 on a convex roll feature. A remotely triggered avalanche was also triggered from 25 m away. Several remotely triggered avalanches have been reported in the last week from up 100m away. Avalanche activity is expected to continue as temperatures rise.

Snowpack Summary

Warm temperatures and strong sun are rapidly changing the upper snowpack. The snow surface is likely to become moist by day on most aspects and elevations. Overnight refreezing may form surface crusts. Watch out when there is no overnight refreeze: rapid weakening during the day is likely.A troublesome weak layer is down 20-60cm. This layer consists of surface hoar and facets overlying a melt-freeze crust. The distribution of the layer is variable, and it may be more problematic in the north of the region. In exposed alpine terrain, recent strong SW winds formed wind slabs in leeward features. Large cornices exist and may become weak with daytime warming. There are three dormant persistent weak layers that we are continuing to track. The late-March crust is down 50-70cm and was reactive last week during the warm period. The mid-March and mid-February layers are typically down between 70 and 100cm and have been dormant for several weeks. These layers have the potential to wake up with sustained warming, a significant rain event, and/or a big cornice fall.

Problems

Loose Wet

Strong sunshine is expected to trigger loose wet avalanches on steep sun-exposed slopes. These have the potential to trigger larger slab avalanches.

Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>Sluffs may trigger deeper instabilities.>

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Persistent Slabs

A touchy interface down 20-60 cm may be triggered by people or with a natural trigger like cornice fall or sunshine.

Dig down to find and test weak layers before committing to a big line.>Be cautious around steep unsupported slopes and convexities.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 4

Cornices

Large cornices are expected to become weak with daytime warming, especially when exposed to the sun. Cornices have the potential to trigger large slab avalanches.

Cornices become weak with daytime heating, so travel early on exposed slopes.>Give cornices a wide berth when travelling on or below ridges.>

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

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

2 - 5

Valid until: Apr 20th, 2015 2:00PM