Avalanche Forecast

Issued: Jan 30th, 2018 5:49PM

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

shorton, Avalanche Canada

South Rockies.

Large destructive avalanches in this region highlight the importance of sticking to simple low-angled terrain and avoiding overhead hazards like cornices.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

WEDNESDAY: Mix of sun and cloud / light to moderate west wind / alpine temperatures around -11 C.THURSDAY: Mix of sun and cloud / moderate west wind / alpine temperatures around -9 C.FRIDAY: Isolated flurries / moderate to strong west wind / alpine temperatures around -7 C.

Avalanche Summary

On Tuesday, a few natural wind slabs (size 2) were reported in the southeast part of the region. A few large deep persistent slab avalanches (up to size 3) have been reported over the past few days, many of which were triggered by cornices on north and east facing slopes. On Sunday, a size 2 deep persistent slab avalanche was triggered by a snowcat on a southeast aspect at 1900m. This avalanche was 180 cm deep and ran on facets sitting on a rain crust buried at the end of November. 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

15 cm of fresh snow and strong winds have formed wind slabs in exposed terrain and fragile cornices along ridgetops. Warm temperatures on Monday left moist snow and crusts up to about 1700 m.About 20-50 cm of recent snow covers a layer of feathery surface hoar in sheltered areas and a sun crust on solar aspects that was buried in mid-January. 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 in mid-December is found at treeline and below treeline elevations. A weak layer of rain crusts and sugary facets buried in late-November exists near the base of the snowpack. 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 strong winds have created wind slabs in leeward areas near ridge crest in the alpine and in exposed treeline areas. Large fragile cornices are also likely near ridge crests.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

Several deeply buried weak layers have the potential to produce large destructive avalanches. Conservative terrain with moderate-angled, supported slopes are good choices.

Watch for signs of instability such as whumpfing, or shooting cracks.Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Valid until: Jan 31st, 2018 2:00PM