Archived

Avalanche Forecast

Mar 3rd, 2016–Mar 4th, 2016

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

Alpine

4: High

The avalanche danger rating in the alpine will be high

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: Kootenay Boundary.

Storm slabs are highly reactive to human-triggering and conservative terrain selection remains critical for the next few days. Extra caution is required on south-facing slopes in the afternoon if the sun pokes out.

Confidence

High

Weather Forecast

FRIDAY: Cloudy with sunny breaks and a chance of flurries late in the day. Freezing levels reaching 1800-2000 m late in the day with moderate to strong southwesterly ridgetop winds. SATURDAY: Periods of snow bringing another 5-15cm. Freezing levels steady around 2000-2200 m with strong southwesterly ridgetop winds. SUNDAY: Periods of snow. The freezing level is around 1600-1800 m and ridge winds ease to light and variable.

Avalanche Summary

On Wednesday there was a report of a size 2.5 avalanche that was remotely triggered by a group on a ridge. This avalanche occurred in the northern part of the region on a NE aspect. In addition, there were reports of numerous size 1.5-2 natural storm slab avalanches and several size 2 explosive triggered storm slabs. These were on a variety of aspects between 1900 and 2100 m elevation. The slabs were releasing on the late-February crust/surface hoar layer down 30 cm.

Snowpack Summary

Recent storm accumulations varied widely across the region, but were generally highest around Nelson where up to 45cm of new snow was reported. Significant wind transport has been noted so expect to find deeper, more destructive slabs in exposed lee terrain. The new snow overlies a new layer of well-developed surface hoar (up to size 20mm) which is very reactive to human triggers. This layer is widespread above 1700m except on south aspects where the interface was cooked by the sun and now exists as a buried crust. 80-100cm below the surface you will likely find the mid-February crust/facet/surface hoar layer. Although this layer has become less likely to trigger, avalanches failing at this interface could be large and destructive.

Avalanche Problems

Storm Slabs

Recently formed storm slabs overlie a touchy weak layer and are primed for human-triggering. Particularly touchy wind slabs have formed in leeward features from recent strong SW winds.

The new snow will require several days to settle and stabilize.>Avoid freshly wind loaded features.>Use small slopes with low consequence to test reactivity of the new snow.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely - Very Likely

Expected Size: 1 - 4

Persistent Slabs

An old weak layer down 80-100cm has been dormant recently but could wake up with substantial warming, sun, or new load. Heavy triggers such as cornice falls or smaller avalanches have the potential to step down to this layer.

Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar. >Dig down to find and test weak layers before committing to a big line. >

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Unlikely - Possible

Expected Size: 3 - 6