Avalanche Forecast

Issued: Apr 20th, 2013 10:41AM

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

swerner, Avalanche Canada

Cariboos.

The Public Avalanche Forecasts and Danger Ratings will come to an end on Tuesday. General spring messaging will be found under the Forecast Details tab.

Summary

Confidence

Fair - Due to limited field observations

Weather Forecast

The Interior will remain under a cool, dry North-West flow through Tuesday. A slow warming trend will persist until the end of next week.Sunday: Scattered-broken cloud cover, allowing some sunshine through. Â Ridgetop winds will blow light from the North. Freezing levels 900 m and falling to valley bottom overnight.Monday/Tuesday: Mostly clear, sunny skies. Ridgetop winds will blow light from the West. Freezing levels 1400 m in the afternoon and falling to 1000 m overnight.

Avalanche Summary

On Friday, numerous loose wet size 1 avalanches occurred. Additionally, a skier triggered size 1.5 slab avalanche released from an East aspect at 2250 m. The crown depth was 25 cm, width was 30 m and running 40 m in length.

Snowpack Summary

Up to 15 cm of new snow sits on melt-freeze crusts (solar aspects) and smaller surface hoar crystals on Northerly aspects. Touchy wind slabs have built on lee slopes and behind terrain features and cornices are huge and remain a concern, threatening slopes below.Buried 60-100 cm down, exists an interface of crusts and buried surface hoar. This is mainly found at upper elevations on all aspects. It seems to be slowly gaining strength, yet this interface has recently become reactive in regions further south. I would remain suspicious, especially of large, steep high-alpine slopes. Dig down, and test layer of concern.

Problems

Wind Slabs

New snow and moderate winds have built wind slabs on lee slopes and behind terrain features. Large, looming cornices exist on ridgelines and pose a threat to slopes below. Keep your distance from them.

Be cautious as you transition into wind affected terrain.>Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

A weak interface is buried about a metre down. A smaller avalanche stepping down, cornice fall, the weight under a snowmobile, or the weight of a person from a thin-spot trigger point could trigger a large and destructive avalanche.

Be aware of thin areas that may propagate to deeper instabilites.>Dig down to find and test weak layers before committing to a line.>

Aspects: All aspects.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

2 - 6

Valid until: Apr 21st, 2013 2:00PM