Avalanche Forecast

Issued: Jan 24th, 2018 5:07PM

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.

jmcbride, Avalanche Canada

Lizard-Flathead.

Storm snow and wind are adding to an already complex snowpack with a number of buried weak layers that have produced several recent, large avalanches. Simple terrain with no overhead hazard is a good choice should you venture into the backcountry.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Snow. Accumulation 10-20 cm. Ridge wind strong, southwest. Temperature -2. Freezing level lowering to valley bottom.THURSDAY: Mostly cloudy, flurries. Accumulation 5-10 cm. Ridge wind strong, southwest. Temperature -3. Freezing level rising to 1000 m.FRIDAY: Mostly cloudy, light flurries. Accumulation 2-6 cm. Ridge wind strong, southwest. Temperature -4. Freezing level valley bottom.SATURDAY: Cloudy, flurries. Accumulation 2-8 cm. Ridge wind light to moderate, south. Temperature -4. Freezing level valley bottom.

Avalanche Summary

Wednesday numerous explosive and skier triggered storm slab avalanches to Size 2 were reported up to 20 cm deep, with propagations from 20 up to 200 m wide, and running long distances.On Tuesday widespread sloughing and and several storm slabs up to Size 1 were observed in steep terrain. Also a Size 2 was triggered from 50 m away by a snow machine on a northeast aspect at 2050 m. The crown was 120 cm deep and is suspected to have failed on the mid-December weak layer.Reports from Monday included seven deep persistent slabs that were released with small explosives in the alpine in the Fernie area. Sizes ranged from 2.5-3, crown depths averaged about 200 cm and all results indicated the deeply buried late-November crust as the failure plane. These results demonstrate the need for ongoing vigilance with regard to overhead hazards and the ongoing potential for deep, destructive avalanches to occur.

Snowpack Summary

About 40-60 cm of storm snow now covers a layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) as well as sun crust on solar aspects that was buried mid-January. Beneath the mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is buried 90-110 cm below the surface. A weak layer buried mid-December (predominantly surface hoar and/or a sun crust) is around 120-160 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets that developed late-November is near the bottom of the snowpack. All of these layers have produced recent large, destructive avalanches and remain a concern.

Problems

Storm Slabs

New snow and has formed touchy storm slabs and winds have loaded lee slopes near ridge top. These slabs have shown the potential for wide propagations and running long distances.

If triggered, storm slabs may step down to deeper layers and result in large avalanches.Avoid exposure to overhead avalanche terrain, avalanches may run long distances.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Very Likely

Expected Size

1 - 2.5

Persistent Slabs

Several weak layers of concern are buried within the snowpack and have the potential to produce large avalanches. Conservative terrain with moderate-angled, supported slopes are good choices.

Be cautious in shallow snowpack areas where triggering a deeper weak layer is more likely.Watch for signs of instability such as whumpfing, or shooting cracks.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3.5

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