Avalanche Forecast

Issued: Dec 23rd, 2016 5:28PM

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

Ruari Macfarlane, Parks Canada

Waterton Lakes.

Cooling temperatures will exert a slow stabilizing influence on the snowpack. For Saturday, human triggering of Large avalanches remains Likely in specific areas. Be especially cautious in areas of variable snowpack depth.

Summary

Weather Forecast

Saturday: An Upslope flow brings light snowfall and light - moderate Easterly winds. Temperatures fall, from -10 to -15.Sunday: A building ridge causes flurries to taper off, with some afternoon sun possible. -15, light winds.Monday: Return of the Westerlies! Expect: racing clouds, Strong Westerly winds, blowing snow, and rising temperatures.

Snowpack Summary

New snowfall is burying several layers of Hard Wind Slab at all elevations, formed by previous Extreme Westerly winds. In deeper snowpack areas, the Wind Slabs are sitting on a midpack of small facets, which have produced shears in tests. In thin snowpack areas, they are sitting on weak, large, developing Depth Hoar, producing Sudden shears.

Avalanche Summary

Explosives control work at neighboring avalanche operations have been producing Large avalanches daily in Wind exposed terrain, especially in areas that were shallow prior to recent wind loading from the West.Shooting cracks and Whoomphing were observed in pockets of Hard Wind Slab over Depth Hoar in Eastern (shallow snowpack) areas on Friday.

Confidence

Due to the number and quality of field observations

Problems

Persistent Slabs

Nearby operations have reported these failing in the middle of the snowpack, and in some cases stepping down to ground. They are most likely to be triggered in thin Rocky areas, which are more widespread in the Eastern areas of the Park.

Be aware of the potential for wide propagations due to the presence of hard windslabs.Avoid convexities or areas with a thin or variable snowpack.

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

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Wind Slabs

These are more widespread than usual, existing on most aspects and elevations due to the intensity of previous winds. They will be hard to spot under new snowfall. New Wind Slabs will build with forecast Strong Westerlies on Monday.

Watch for whumpfing, hollow sounds, and shooting cracks.Be careful with wind loaded pockets while approaching and climbing ice routes.

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

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Dec 26th, 2016 4:00PM