Avalanche Forecast

Issued: Mar 18th, 2013 10:42AM

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

jfloyer, Avalanche Canada

South Coast.

I expect a natural avalanche cycle to occur in the Coquihalla backcountry areas on Tuesday as the wind increases in the afternoon. Avalanche danger for the alpine along the Duffey is more like CONSIDERABLE.

Summary

Confidence

Poor - Due to variable snowpack conditions

Weather Forecast

Synopsis: A punchy Pacific frontal system will bring heavy precipitation Tuesday night and Wednesday.Tuesday: Day starting clear, but clouding over then moderate snowfall starting in the afternoon. Southerly winds 40 km/h.Tuesday Night: 10-20 cm overnight. Freezing level around 1200 m. Southwest winds increasing to 60 km/h at ridgetop.Wednesday: 10-20 cm new snow. Freezing level around 1500 m. Southwest winds 60 km/h.Thursday: 5-15 cm new snow. Freezing level 800 m. Gusty westerly winds becoming northwest later on.

Avalanche Summary

On Sunday, slab avalanches were easily human-triggered up to size 2 in the Coquihalla on south aspects with 40-60 cm storm snow failing on a crust. 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

Heavy snowfall has continued in the Coquihalla region, with recent storm totals over the last four days of 80 cm. During the same period, around 20 cm fell along the Duffey and around 30 cm in Manning Park. This new snow sits on a crust along the Duffey at elevations below 1900 m. In the Coquihalla region, this crust was not reported to have formed due to the insulating effect of the new snow. Instead, the new snow here sits on wet snow from the previous storm. For all areas, expect extensive wind slabs and cornices in the alpine. A deeper weak layer comprising surface hoar and/or a crust is buried around 70 cm on the Duffey/in Manning Park and more like a metre on the Coquihalla. Natural avalanche activity has subsided on this layer. However, I wouldn't discount the possibility of an avalanche stepping down to this layer, especially in steep alpine terrain. Lower snowpack layers are strong and well settled, although the snowpack may still be susceptible to glide activity (involving the whole snowpack) at lower elevations where it rests on steep, smooth surfaces.

Problems

Storm Slabs

Highly variable snow amounts across the region, as well as variable snowpack structure following the recent wet storm. Wind slabs, new snow over a crust and possibly deeper weak layers, especially in the alpine, are all potential trigger points.

Note recent avalanche activity.>Avoid large alpine features.>Choose well supported terrain without convexities.>Be alert to conditions that change with elevation.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 6

Cornices

Cornices are reported to be large and may become unstable, especially with solar radiation during the day.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 19th, 2013 2:00PM