Avalanche Forecast

Issued: Jan 24th, 2018 3:55PM

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.

jmcbride, Avalanche Canada

Northwest Coastal.

Storm snow and wind are building reactive slabs particulary on leeward slopes at upper elevations, while buried weak layers have produced recent avalanches at lower elevations.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Light flurries. Accumulation trace. Ridge wind light, southeast. Temperature -8. Freezing level valley bottom.THURSDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, southeast. Temperature -5. Freezing level 300 m. FRIDAY: Mostly cloudy, flurries. Accumulation 2-6 cm. Ridge wind light to moderate, south. Temperature -6. Freezing level valley bottom.SATURDAY: Mix of sun and cloud. Ridge wind light, east. Temperature -9. Freezing level valley bottom.

Avalanche Summary

On Tuesday there were reports of natural storm slab avalanches up to size 2 failing on mid-January interface and ski cut results producing storm slab avalanches to size 1.5 near ridge crest. In the Bear Pass area numerous natural wind slab failures from Size 1-2.5 were observed on wind-loaded northerly features as well as Size 1.5-2.5 naturals that ran on the mid-December crust layer between 600-1200 m.Monday, areas north of Stewart reported numerous natural loose storm snow avalanches on most aspects, and one skier remote Size 1.5 storm slab avalanche on a southerly aspect at 1400 m and is suspected to have failed on the mid-December interface following a large whumpf.Reports from Saturday included one observation of a remotely (from a distance) triggered Size 1.5 storm slab releasing on a steep north-facing roll at 1100 m. This is suspected to have run on surface hoar buried beneath the recent snow accumulations.

Snowpack Summary

Approximately 40-80 cm of recent storm snow covers a widespread crust as well as surface hoar in isolated areas at mid elevations that were buried mid-January. This surface hoar is more likely to exist in sheltered areas at treeline and below. Professionals have also been monitoring a few mid-pack layers within the snowpack including a crust and surface hoar layer that was buried early-January and now lies 60-100 cm below the surface, and a similar layer buried mid-December that now lies 80-120 cm below the surface. Both of these layers have been reactive in recent snowpack tests producing moderate to hard, sudden results and have produced recent large, natural avalanches particularly in northern areas of the region.The lower snowpack is generally strong, with the exception of areas around Stewart and further north where a basal crust and facets exist.

Problems

Storm Slabs

Winds have formed areas of wind slab at higher elevations near ridge crests. In sheltered areas near treeline and below the storm snow has settled into a cohesive soft slab above the recently buried mid-January crust/ surface hoar layer.

Watch for wind loaded areas, especially near ridge crests and roll-overs.Caution on steep slopes and convex rolls where a recent crust/surface hoar has been buried.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

Buried weak layers in the snowpack have produced recent large avalanches in steep, unsupported terrain below treeline.

Avoid shallow, or thick to thin snowpack areas where triggering a deeper layer is more likely.Watch for signs of instability such as whumpfing, or cracking.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Jan 25th, 2018 2:00PM