Avalanche Forecast

Issued: Jan 21st, 2017 4:10PM

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

mgrist, Avalanche Canada

Kootenay Boundary.

In the southwest corner of the region there's an unusually weak snowpack. Conditions are primed for people triggering avalanches. Don't let the lure of deep powder draw you into terrain that's inappropriate for the conditions.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Some unsettled weather for Sunday and only a few flurries are expected. Clear fine weather for early next week.SUNDAY: Flurries with 5-10 cm possible, moderate southerly winds. Freezing levels remaining around 1200m and alpine high temps to -4 Celsius.MONDAY: Cloudy. Light northerly wind and freezing level around 1100m, alpine high temperatures to -5 Celsius.TUESDAY: Cloudy with sunny breaks. Light northerly wind and freezing level around 900m, alpine high temperatures to -8 Celsius.

Avalanche Summary

We had a great MIN report of a cornice-triggered Size 2 on Friday near Cabin Peak in the Bonnington range. The initial failure was in the storm slab on a southeast aspect near 2000m, which stepped down to trigger a weaker layer deeper in the snowpack.We also had a MIN report of a skier-triggered Size 2 on Thursday in the Rossland range. The failure was a deep persistent slab on a cross-loaded west-facing slope, possibly running on mid December facets or even the November rain crust / facet combination. Avalanche control in the eastern part of the region gave several Size 2.5 - 3 avalanches running within the storm slab layers on easterly aspects, and some gouging down to ground or into faceted layers deeper in the snowpack, and running full path.

Snowpack Summary

By Friday morning another 2-10 cm added to the previous 25-45 cm of fresh snow this week, accompanied by moderate to strong southerly winds. This has resulted in touchy storm and wind slabs bonding poorly to the previous snow surface that includes facets and large surface hoar on sheltered slopes and/or a sun crust on steep sun-exposed aspects, as well as wind-affected surfaces (e.g. hard wind slab, sastrugi, scoured crust, etc.) in exposed areas. In some areas of the Rossland range, the mid-November rain crust / facet layer is now likely down 50-90 cm and has become reactive with continued loading and warming. In thin rocky areas, particularly in the Rossland range, recent reports include easy sudden collapse snowpack test results on facets down 120-150 cm near the ground. This deep persistent weakness may also become reactive with continued loading and warming.

Problems

Storm Slabs

New snow is bonding poorly to the previous snow surface. Expect the avalanche likelihood and size to increase with increased snow and wind-loading. Slabs will be particulary deep and touchy on wind-loaded northerly aspects near ridge crests.

Watch for signs of instability such as whumpfing, or cracking. The new snow will require several days to settle and stabilize.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

Several different persistent weak layers are buried 60-150cm deep and have started to become reactive to human triggering. Conservative terrain use is essential, especially in the southwest portion of the region.

Be aware of the potential for full depth avalanches due to deeply buried weak layers.Carefully evaluate terrain features by digging and testing on adjacent, safe slopes. If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Jan 22nd, 2017 2:00PM