Avalanche Forecast

Issued: Jan 28th, 2018 4:34PM

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

mgrist, Avalanche Canada

Purcells.

Significant uncertainty exists with forecast snowfall amounts: If you see more than 30 cm of new snow consider the danger to be HIGH and avoid all avalanche terrain, including overhead hazard.

Summary

Confidence

Low - Forecast snowfall amounts are uncertain

Weather Forecast

Monday: 10 cm snow Sunday overnight into Monday with another 10-20 cm snow during the day. Moderate to strong south-westerly winds. Alpine temperature near -2.Tuesday: 5-10 cm snow. Light to moderate south-westerly winds. Alpine temperature near -5. Wednesday: Cloudy with isolated flurries. Light south-westerly winds. Alpine temperature near -5.More information can be found in the Mountain Weather Forecast.

Avalanche Summary

On Saturday near Kimberley, skiers remote-triggered two Size 2 avalanches, by a convex roll near 2000m elevation. Crown height was 60-70cm, suggesting the snow ran on the mid January layer. See the MIN report for more details. On Friday we received reports of several explosives-triggered persistent slab avalanches (to Size 3), primarily on northerly aspects above 2200m, running on the Jan 5th surface hoar layer. With consistent loading over the next two days, human triggering will remain likely and avalanches could be surprisingly large due to the structure of the snowpack.

Snowpack Summary

The current snowpack is complex, with three active weak layers that we are monitoring.1) 50-80 cm of recent storm snow overlies a crust and/or surface hoar layer (from mid-January). The crust is reportedly widespread, except for possibly at high elevations on north aspects. The surface hoar is 10 to 30 mm in size, at all elevation bands. The recent snow fell with strong south winds, producing wind slabs and cornices in lee features. 2) Deeper in the snowpack (down 60-90 cm), a persistent weak layer known as the early-January layer is present at all elevation bands, and composed of surface hoar on sheltered slopes and sun crust on steep solar aspects. Recent snowpack tests have shown sudden fracture characters with moderate loads and high propagation potential. 3) Another persistent weak layer that was buried mid-December is 70 to 110 cm deep and consists of a facet/surface hoar/crust combination. It is most problematic at and below tree line.A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.

Problems

Storm Slabs

Forecast strong winds, heavy snowfall and warming temperatures are a recipe for widespread avalanches. A storm slab could step down to a deeper weak layer, creating a surprisingly large avalanche.

If triggered storm slabs may step down to deeper layers and result in very large avalanches.Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 3

Persistent Slabs

Several weak layers are buried in the snowpack, creating very large avalanches when triggered.

Avoid open slopes and convex rolls where buried surface hoar may be preserved.Avoid thin, rocky or sparsely-treed slopes.Use conservative route selection, bearing in mind that avalanches may be surprisingly large.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Jan 29th, 2018 2:00PM