Avalanche Forecast

Issued: Feb 15th, 2017 5:39PM

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

mgrist, Avalanche Canada

Kootenay Boundary.

We're into a period of HIGH danger with rapid loading of the snowpack on Wednesday into Thursday: rain to treeline and heavy snow in the alpine.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

Warm and wet on Wednesday through Thursday. Cooling with isolated flurries on Friday, and Saturday. THURSDAY: Rain or wet snow (20-30 mm / cm) Wednesday overnight and another 20-30 mm / cm during the day Thursday. / Moderate southerly winds / Freezing level around 1600 m. FRIDAY: Mostly cloudy with lisolated flurries possible (5-10cm) / High temperatures to -1 Celsius / Light westerly winds / Freezing level around 1300 m. SATURDAY: Cloudy with light snow (5-15cm) / Ridge winds light southerly / Freezing level around 1100m / High temperatures to -2 Celsius.

Avalanche Summary

In the Rossland Range deep persistent slabs to Size 2 were reported on southeast and west aspects around 2000m. A thin snowpack or solar triggered sluffs stepping down to weaker faceted layers were the culprits. Of particular note was a Size 3 natural avalanche on Wolf ridge near Kootenay pass on Monday - the sun's effect is significant! See the great photo in the MIN report (here).

Snowpack Summary

The recent warming and sunny conditions gave us a widespread sun crust on all but high northerly (and some westerly) aspects, where there is still some cold snow to be found. These will be excellent sliding surfaces for incoming new snow.At the end of last week up to 30cm additional snow fell (mostly near Nelson) and brought the recent storm snow total to 65-100cm, creating touchy storm slabs at all upper elevations and aspects. Slabs were reported as very reactive to human triggers and are sitting on a variety of surfaces; including scoured surfaces in wind exposed terrain, surface hoar (size 2-3 mm) in sheltered locations, and sun crust on steep solar aspects.Snowpack tests near the Valhallas have given moderate, propagation-likely results down 50-70cms on the Feb 3rd interface. Areas with a shallower snowpack (less than 150 cm) have a generally weak snowpack structure with sugary facets near the ground. This includes shallow alpine slopes and most of the Rossland range. It is possible for storm slab avalanches to step-down to these deeper weak layers, resulting in large, destructive avalanches.

Problems

Loose Wet

Where the precipitation falls as rain, watch out for loose wet where the snow is soft and cohesionless. Avoid getting pushed into terrain features like gullies and cliffs, where even small slides could have large consequences.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.Avoid lingering in runout zones.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Storm Slabs

The warming trend, strong winds and heavy precipitation will make storm and wind slab avalanches likely in the alpine.

Watch for signs of instability such as whumpfing, shotting cracks, or recent natural avalanching.Use small slopes with low consequence to test the bond of the storm snow.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

Storm slabs may step-down to deeper weak layers, resulting in large, destructive avalanches.

Avoid likely trigger spots such as steep and rocky areas with a shallow snowpack.Wait to see how the snowpack responds to increased loads before venturing out into bigger terrain

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 16th, 2017 2:00PM