Avalanche Forecast

Issued: Dec 15th, 2011 8:19AM

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

triley, Avalanche Canada

South Columbia.

Summary

Confidence

Fair - Forecast snowfall amounts are uncertain on Friday

Weather Forecast

A few cms (3-5) are forecast for overnight Thursday into Friday. The wind is expected to be light from the west on Friday with temps around -5.0 C at treeline and freezing levels about valley bottom. We may see broken skies during the day on Friday as a bit of a ridge moves through before the next wave of snow starts Friday afternoon. It looks like me may get up to 15 cms by Saturday morning. Moderate to strong winds from the southwest are forecast during this storm. The bulk of the moisture is expected to be a bit North of Revelstoke. A series of Pacific disturbances should continue for the next few days, timing and snow amounts are a bit unsure at this time.

Avalanche Summary

No reports of new avalanches. It may take another day or two of additional new snow and wind to develop a new storm snow problem.

Snowpack Summary

Another 5-10 cms in the region brings the new storm snow up to 5-20 cms. This overlies surface hoar, surface facets, old windslabs and sun crusts (on steep south through west aspects). Winds have been sporadic in this period, with some strong northerlies intermingled with the more dominant light to moderate westerlies. There are isolated new soft slabs in immediate lee locations and some surface sluffing in more protected areas where the surface hoar is more prominent. Moving forward, the avalanche danger will increase as the load increases (either by new snow or wind). Be locally aware of changes and if obvious signs of instability are present (cracking, whumphing, recent activity on adjacent slopes) or rapid loading is taking place (heavy snowfall or strong winds) then scale down your terrain choices accordingly.Deeper in the snowpack there is a rain crust buried between 20-35cm. This crust extends as high as 2200m and some faceting (weakening) has been observed around the crust. Deeper still, the early November surface hoar remains a layer of concern. Buried 100-150cm it is unlikely to trigger, but consequences of triggering would be a large (up to size 3.0) destructive avalanche.

Problems

Wind Slabs

This problem is changing from old wind slab on a non-persistent layer, to new soft wind slab on a recently buried surface hoar and/or crust layer. Remember that old wind slabs exist, and that new more touchy wind slabs are developing.

Aspects: North, North East, East.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 3

Persistent Slabs

Highly variable snow depths make this very difficult to predict. Weaker thin spots on convexities or around protruding rocks/clumps of small trees may be likely trigger locations for deeper avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

2 - 5

Valid until: Dec 16th, 2011 8:00AM