Avalanche Forecast

Issued: Apr 19th, 2015 8:30AM

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

triley, Avalanche Canada

Northwest Coastal.

This is the last avalanche bulletin with danger ratings for this region this season.

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

Warm and windy overnight with overcast skies and some light precipitation. Coastal areas should see up to 15 mm of precipitation on Monday with a freezing level around 1800 metres. Inland areas are likely to get less than 5 mm of precipitation as the system moves south along the coast and is not forecast to push inland. Stormy conditions are expected to continue in the Northwest.

Avalanche Summary

We have a report from the Nass Range near Rosswood from Friday, of a larger slab avalanche with 100 cm crown that we suspect was from a convex feature in the alpine on a westerly aspect. On Thursday, numerous natural slab avalanches up to size 2 were reported and a widespread loose wet avalanche cycle occurred when the sun poked out in some areas. A larger size 3 slab was seen from across the valley at Shames, maybe a day old or so by now. On Tuesday, the region saw a natural cycle up to size 3 was from steep alpine and treeline terrain. Reports suspect that some of these naturals are stepping down to the old interfaces buried April 9 th and mid- March. With temperatures rising into the alpine, cloudy skies and light rain forecast, the snowpack will deteriorate and natural avalanche activity will continue. Lower elevations which have become rain soaked and natural loose wet avalanches from steeper terrain features are expected.

Snowpack Summary

At upper elevations 35- 80 cm of recent storm snow has blanketed the region. The new snow has been redistributed by strong southwest winds into wind slabs on leeward slopes. Solar aspects may have a new sun crust. The lack of bond between the new wind slabs and storm slabs over the older snow surfaces buried on April 9 th (surface hoar, crusts and facets) is the primary concern. The March 25th persistent surface hoar / crust layer reportedly became reactive with the recent storm, however; observations are very limited and it may have just been in a localized area. With forecast warming well above mountain peaks this pwl should remain on your radar, it may re-awaken, initiating very-large and destructive avalanches. Moist rain soaked snow exists at lower elevations.

Problems

Storm Slabs

Storm slabs are touchy, especially where they sit on a buried facet, surface hoar and/ or crust interface. Strong winds have built touchy wind slabs on leeward slopes and behind terrain features. Human triggering is likely.

If you are increasing your exposure to avalanche terrain, do it gradually as you gather information.>Avoid freshly wind loaded features.>Pay attention to overhead hazards like cornices, especially if the sun pokes out.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 5

Persistent Slabs

Additional storm snow loading on the mid- March persistent weak layer has brought it back to life. Smaller storm slab avalanches may step down to this layer, initiating large, destructive avalanches.

Be aware of the potential for large avalanches due to the presence of buried surface hoar and facets on a crust.>Use conservative route selection, stick to moderate angled terrain with low consequence.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 5

Loose Wet

Warm temperatures and rising freezing levels will deteriorate the snowpack quickly. Watch for signs of instabilities like avalanches, moist surface snow and snowballing.

Pay attention to overhead hazards like cornices.>Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 4

Valid until: Apr 20th, 2015 2:00PM