Avalanche Forecast

Issued: Mar 16th, 2013 9:41AM

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

jfloyer, Avalanche Canada

South Coast.

Variable snowpack conditions, particularly at upper treeline and alpine elevations. The snowpack is proving slow to recover following the recent big storm.

Summary

Confidence

Fair - Due to variable snowpack conditions

Weather Forecast

Synopsis: Northwest flow will bring occasional flurries and cooler temps until Tuesday, when a low pressure system is expected to impact the region.Sunday and Monday: Occasional flurries. Sunny breaks in the cloud giving daytime warming both days. Afternoon freezing level around 700 m. Winds mostly light nothwesterly, but occasionally gusty.Tuesday: Moderate, maybe heavy snowfall starting in the afternoon. Models currently disagree with track and intensity of this system. Freezing level going to around 1500 m. Southwest winds to 60 km/h at ridgetop.

Avalanche Summary

On Friday, a size 2.5 natural loose wet avalanche was reported from the Coquihalla. Along the Duffey, small skier-triggered avalanches could be triggered on north aspect slopes at treeline, with crowns of 30 cm in the recent storm snow.

Snowpack Summary

The recent storm delivered around 60 cm of heavy snow at upper elevations and a mix of rain and snow below around 1900 m. Below 1500m, the snowpack was reported to be isothermal as of Friday afternoon. On Friday night, 5-15 cm new snow fell. This insulating layer will further delay the re-freezing process, despite cooler temperatures. Below the recent storm snow lies one or two weak layers buried approximately 50 cm below the surface. These comprise faceted snow, surface hoar and/or a crust. As a result of all these factors, the snowpack structure is highly variable at this time. It may change dramatically with only a subtle change in elevation, aspect, wind or sun exposure. With further cooling, the upper snowpack should start to bond better. However, with the amount of moisture and the insulating effect of the new snow, expect this to take longer than usual. The mid-pack is strong and well settled, although the entire snowpack will remain volatile below 1500m until it has a chance to freeze.

Problems

Storm Slabs

There's a lot of uncertainty surrounding the new/old snow interface which consists of surface hoar, old wind slabs and crust. We need to gain more information on this interface before we start thinking about bigger objectives.

Avoid large alpine features.>Avoid freshly wind loaded features.>Avoid open slopes and convex rolls where buried surface hoar may be preserved.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 6

Cornices

Do not travel on slopes that are exposed to cornices overhead.>Give cornices a wide berth when travelling on ridges.>Pay attention to overhead hazards like cornices.>

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 17th, 2013 2:00PM