Avalanche Forecast

Issued: Jan 27th, 2018 4:26PM

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

jmcbride, Avalanche Canada

South Rockies.

With several buried weak layers, the snowpack is primed for human triggering. Best to stick to conservative terrain, avoid wind-loaded areas, and back off if you see classic warming signs like whumpfing or cracking.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

TONIGHT: Cloudy, light flurries. Accumulation trace. Ridge wind moderate to strong, west. Temperature -10. Freezing level valley bottom.SUNDAY: Cloudy, flurries. Accumulation trace. Ridge wind light, southwest. Temperature -6. Freezing level valley bottom. MONDAY: Cloudy, flurries. Accumulation 2-5 cm. Ridge wind strong, southwest. Temperature near 0. Freezing level rising to 2000 m.TUESDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind strong, west. Temperature near 0. Freezing level lowering to 800 m.

Avalanche Summary

On Thursday explosive control work in the Castle area triggered a Size 3 avalanche from a shallow area that propagated and failed on the late-November layer deep in the snowpack. While in the Bull River area a natural Size 1.5 wind slab avalanche was observed on a northwest aspect at treeline and a natural Size 2 in a west-facing cutblock at 1600 m was reported to have failed on the mid-December layer.The snowpack in the region remains suspect with several buried weak layers displaying classic signs of instability such as whumpfing and cracking. The recent video posted to the Avalanche Canada South Rockies field team Facebook page paints a pretty clear picture. https://www.facebook.com/avcansouthrockies/videos/1894352117306941/.

Snowpack Summary

Amounts vary across the region however, about 20-50 cm of recent storm snow now covers both a new layer of feathery surface hoar in sheltered areas as well as sun crust on solar aspects buried mid-January, and about 30-60 cm below the surfaces lies the early-January surface hoar layer.About 60-80 cm below the surface a weak layer of feathery surface hoar crystals and/or sun crust buried mid-December is found at treeline and below treeline elevations. Near the base of the snowpack the weak early-season layer of rain crust and sugary facets buried late-November exists. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread. Snowpack depths are also variable across the region and typically thinner in northern areas than in areas to the south.

Problems

Wind Slabs

New snow and wind this week have created wind slabs in leeward areas near ridge crest in the alpine and in exposed treeline areas. These slabs are touchy and have been reactive to natural triggers in recent days.

Use caution in lee areas in the alpine and treeline. Wind and storm snow have formed touchy slabs.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

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.

Watch for signs of instability such as whumpfing, or shooting cracks.Be aware of thin snowpack areas where deeper weak layers may be more sensitive to triggering.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Valid until: Jan 28th, 2018 2:00PM