Avalanche Forecast

Issued: Nov 26th, 2012 8:50AM

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.

Peter, Avalanche Canada

Northwest Coastal.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the forecaster's blog for further details on interpreting early season bulletins.

Summary

Confidence

Poor - Due to limited field observations

Weather Forecast

Synopsis: A ridge of high pressure over southern BC should maintain dry conditions on Tuesday; however, expect thickening cloud as a frontal system approaches the region from the west. The system should give moderate precipitation on Wednesday and Thursday. Tuesday: Increasing cloud with flurries possible late in the day. Freezing level at around 500 m. Winds light from the southwest. Wednesday: Periods of snow – 10-20 cm. Freezing level steady at around 300 m. Thursday: Periods of snow or flurries – 5-10 cm. Freezing level at the surface.

Avalanche Summary

A few small natural slab avalanches were reported in the Shames backcountry on Sunday. These were generally 20 cm deep, failing within the recent storm snow. Some larger avalanches (up to size 2.5) were also observed in surrounding areas. Slope testing on several small steep slopes on Sunday afternoon produced no results. Human triggered avalanches remain possible on Tuesday, particularly in exposed wind loaded terrain. The potential for natural avalanches may increase again on Wednesday with more snow and stronger winds forecast.

Snowpack Summary

60-80 cm of storm snow fell in the past few days, accompanied by shifting south to northwest winds. Weaknesses may exist within or under the storm snow. Expect deep wind slabs in exposed lee terrain and in cross-loaded gullies or terrain features. A recent profile at 1200m in the Shames area showed a thin layer of facets sitting on a crust 35cm off the ground. A snowpack test produced easy results on this layer, but the resistant fracture didn't propagate across the entire column. Total snowpack depth are probably around 150 cm in most treeline areas and deeper but more variable in the alpine. The snowpack below treeline may still be below threshold depth for avalanches in some areas. Check out the Skeena/ Babine discussion forum for more information from the area.

Problems

Wind Slabs

Recent strong winds have created deep wind slabs on a variety of aspects, which may be sensitive to triggering on steep convex shaped slopes.

Use ridges or ribs to avoid pockets of wind loaded snow.>

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

2 - 4

Persistent Slabs

A crust near the base of the snowpack remains a concern. It may be difficult to trigger an avalanche on this layer, but if you do the consequences could be very serious.

Whumpfing is direct evidence of a buried instability.>Carefully evaluate and use caution around thin snowpack areas.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 5

Valid until: Nov 27th, 2012 2:00PM