Avalanche Forecast

Issued: Mar 17th, 2012 11:07AM

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

pgoddard, Avalanche Canada

Sea To Sky.

Avalanche danger ratings in the alpine on Sunday and Monday are HIGH where direct sunshine is affecting the slope. If it's cloudy, assume the danger is CONSIDERABLE.

Summary

Confidence

Fair - Timing or intensity of solar radiation is uncertain

Weather Forecast

Sunday: Locally variable light convective snow showers, amounting to a few cm. Sunny breaks in the afternoon. Generally light winds. Freezing level near 600m.Monday: Scattered cloud. Light winds. Cool in the morning and warming by afternoon with the influence of sunshine. Freezing level near 600m.Tuesday: Moderate snow and moderate to strong south-westerly winds. Freezing level between 500m and 1000m.

Avalanche Summary

Avalanches have been reported all week. On Friday, a number of natural and explosives-triggered storm snow avalanches in the size 1-2 range were reported, many on lee or cross-loaded north-east to north-westerly aspects. Reports of natural size 2-3, and numerous skier or explosives-triggered size 1-1.5 avalanches came in on Thursday on a variety of aspects. On Tuesday a natural avalanche cycle occurred up to size 3 on north to north-east aspects. Cornices reached their threshold and triggered slopes up to size 2.5 below. On Monday, a skier was partially buried and two others escaped a size 2 slab on an east aspect at 1500m, which failed on a crust. Natural and skier-remote triggered avalanches to size 3 were also observed on a variety of aspects and elevations, some failing on the mid-February weakness. Unsettled weather conditions continue. It may take several days for recent storm snow to settle out. If the sun shines through in your local mountains, expect strong solar radiation, snowpack deterioration, and elevated avalanche danger.

Snowpack Summary

In the past week 100-180 cm storm snow has fallen, accompanied by strong south-westerly winds. Storm slabs and wind slabs continue to build. Cornices are large, some reaching threshold and triggering the slopes below. The additional weight of new storm and wind slabs may step down and trigger a deep weakness, formed in mid-February. Recent test results on this layer produced hard sudden planar results. Very large avalanches are possible, which could be remote-triggered, triggered mid-slope, and/or propagate into low-angled terrain. The average snowpack depth at treeline is 350 cm.

Problems

Wind Slabs

Wind slabs lurk below ridges, behind terrain features and in gullies. These may be buried by new snow, making them hard to spot.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 6

Storm Slabs

Up to 180 cm of storm snow has fallen in the past week. Storm slabs may fail naturally with the first blast of sunshine, or could be triggered by the weight of a person. They are also overloading persistent weak layers.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 6

Persistent Slabs

Persistent weaknesses, now about 1.5m deep, demand respect. The potential for remote triggering, step down avalanches, and wide propagations makes this persistent slab problem particularly intimidating and tricky to manage.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

4 - 8

Valid until: Mar 18th, 2012 9:00AM