Avalanche Forecast

Issued: Feb 5th, 2018 4:54PM

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

Avalanche Canada jmcbride, Avalanche Canada

Wind on Tuesday will continue to load recent storm slabs especially at upper elevations and wind-exposed areas. Choose conservative, well-supported terrain. Be aware of overhead hazards, large avalanches have run long distances in recent days.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TUESDAY: Mainly cloudy. Ridge wind moderate, west. Temperature -8. Freezing level valley bottom.WEDNESDAY: Cloudy, light flurries. Accumulation trace. Ridge wind moderate to strong, west. Temperature -4. Freezing level 1400 m.THURSDAY: Snow. Accumulation 20-30 cm. Ridge wind light gusting strong, east. Temperature -4. Freezing level 1300 m.

Avalanche Summary

In the neighboring Lizard Range the east facing Mt. Corrigan slide path produced a very large natural avalanche Saturday. The avalanche is estimated to be a size 4.0, and it took out mature timber in the path as it overran the Flathead FSR south of Corbin. .Photos here. Reports are limited, but there was one 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. See Report here. A few small wind slabs were triggered by skiers in lee terrain on Thursday and Friday.A few large persistent slab avalanches that released during last weekend's storm were observed last week as well. These avalanches failed on deep weak layers from November and December, resulting in large avalanches (size 3). Most were triggered by cornices falling on north and east facing slopes.

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

Storm Slabs

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
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.
Extra caution needed around cornices with current conditions.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Be aware of the potential for large, deep avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Feb 6th, 2018 2:00PM