Avalanche Canada jmcbride, Avalanche Canada

South Rockies Avalanche Forecast

Feb 6th, 2018 4:46PM

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.

New snow and wind on Wednesday and into Thursday will continue to build wind slabs in open areas. Choose conservative, well-supported terrain and be aware of overhead hazards. Large avalanches have run long distances in recent days.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

TONIGHT: Mainly cloudy, light flurries. Accumulation 2-4 cm. Ridge wind strong, west. Temperature -10. Freezing level valley bottom.WEDNESDAY: Cloudy, flurries. Accumulation 4-8 cm. Ridge wind moderate to strong, west. Temperature -4. Freezing level 1200 m.THURSDAY: Cloudy, flurries. Accumulation 10-20 cm. Ridge wind light, northeast. Temperature -20. Freezing level valley bottom.FRIDAY: Sunny. Ridge wind light, north. Temperature -15. Freezing level valley bottom.

Avalanche Summary

On Monday ski cuts in the Castle area produced numerous small (size 1) wind slab results on freshly wind-loaded features.On Saturday in the neighboring Lizard Range, the east facing Mt. Corrigan slide path produced a very large natural avalanche estimated to be a size 4.0, which took out mature timber in the path as it overran the Flathead FSR south of Corbin. Reports are limited, but there was also an explosive triggered wind slab avalanche east of the divide on Saturday. There was likely natural wind slab activity in the northeast part of the region where the heaviest accumulations occurred.On Friday, a snowmobiler was partially buried by a size 2 avalanche in the Alexander Creek drainage. The avalanche occurred on a north aspect around 2000 m and failed on weak snow near the ground. A few small wind slabs were triggered by skiers in lee terrain on Thursday and Friday.

Snowpack Summary

An upslope storm has delivered lots of cold low density snow east of the divide since Saturday (20-40 cm). The distribution of new snow is highly variable, and so are the surface snow conditions. The western parts of the region in BC were relatively warm with less snow, while areas in Alberta and around the divide were much colder and windier which likely formed touchy wind slabs in open terrain.The lower snowpack in this region is weak, with a number of concerning weak layers. A layer buried mid-January is composed of surface hoar on sheltered aspects and a sun crust on solar aspects is now 60-80 cm deep. Another surface hoar layer from early-January is buried 70-90 cm deep. A widespread weak layer from mid-December composed of facets, crusts, and surface hoar is 100-150 cm deep. Finally, a rain crust with sugary facets buried in late-November is near the bottom of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.

Problems

Wind Slabs

An icon showing Wind Slabs

Likelihood

Likely

Expected Size

1 - 2
New snow and strong wind will add to recently formed touchy slabs, especially at higher elevations and in wind-exposed terrain. Snowfall amounts have varied across the region so some areas may have extra thick and touchy storm slabs.
Be cautious as you transition into wind affected terrain.Use conservative route selection, choose moderate angled and supported terrain with low consequence.If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Aspects:

North, North East, East, South East, South.

Elevations:

Alpine, Treeline.

Deep Persistent Slabs

An icon showing Deep Persistent Slabs

Likelihood

Possible

Expected Size

2 - 3
Several deeply buried weak layers have the potential to produce large avalanches reaching run out zones. Cornices have been a recent trigger for very large avalanches. Avoid shallow rocky snowpack areas where human triggering may also be possible.
Be aware of the potential for large, deep avalanches.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Extra caution needed around cornices with current conditions.

Aspects:

All aspects.

Elevations:

All elevations.

Valid until: Feb 7th, 2018 2:00PM