Avalanche Forecast

Issued: Apr 17th, 2015 9:04AM

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

pgoddard, Avalanche Canada

Cariboos.

Danger ratings reflect conditions during the hottest parts of the day. Time your travel to take advantage of cool temperatures.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Precipitation ends on Saturday, leading into three days of warm, dry weather with light winds. The freezing level climbs to 2200 m by Sunday and rises further to 2500 m on Monday.

Avalanche Summary

On Thursday, a naturally-triggered size 2.5 wind slab was observed on a NE aspect at 2000 m. Numerous loose wet avalanches also failed in response to warming. On Wednesday, loose wet avalanches to size 1.5 were reported below 2100m. Widespread wind slabs were reported in the alpine and treeline. Recent whumpfing suggests human-triggered slabs may still be possible, with highest concern on sheltered north aspects. Sun and rising temperatures are likely to lead to avalanche activity wherever the snow is warming up.

Snowpack Summary

Warm temperatures and strong sun are rapidly changing the upper snowpack. On Thursday, a moist snow surface was reported to 2300m elevation on north aspects and is expected to ridgetop on solar aspects. Overnight refreezing is expected to form a widespread surface crust. Down 30-40cm is a weak layer that was buried last Friday and has been reactive recently. This layer consists of surface hoar and facets overlying a melt-freeze crust. 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. At the base of the snowpack, facets exist. 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

Possible - Likely

Expected Size

1 - 2

Persistent Slabs

A weak crust/surface hoar layer down 30-40cm may still be reactive to human-triggering. Strong SW winds have loaded leeward terrain features in the alpine. The layer is most reactive on north aspects in the alpine.

Be cautious around steep unsupported slopes and convexities.>Avoid freshly wind loaded features.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

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 18th, 2015 2:00PM