Avalanche Forecast

Issued: Feb 6th, 2019 4:53PM

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

Avalanche Canada cgarritty, Avalanche Canada

Visible patterns of wind loading will help you to navigate around unstable pockets of wind slab. The less obvious concern is a persistent slab problem that exists from about 1900-1600m. Manage it by selecting conservative, low consequence slopes.

Summary

Confidence

Moderate -

Weather Forecast

Wednesday night: Clear with cloudy periods. Light west or northwest winds.Thursday: Cloudy with sunny periods and isolated flurries with a trace of new snow, continuing overnight. Light southwest winds, increasing to strong northwest in the alpine. Alpine high temperatures around -16.Friday: Cloudy with continuing flurries bringing about 5 cm of low density new snow, continuing overnight. Light northeast winds. Alpine high temperatures around -17 and cooling over the day.Saturday: Cloudy with continuing flurries bringing about 3 cm of new snow and new snow totals to around 10 cm. Light northeast winds with moderate to strong southeast winds in the alpine. Alpine high temperatures around -25.

Avalanche Summary

Another 50 cm-deep size 1.5 persistent slab was triggered with a ski cut on Monday. This occurred on a north aspect at 1720 metres. This is the latest of several recent observations of persistent slab avalanches failing on the persistent weak layer that was buried in mid-January. This layer is described in the Snowpack Summary below.While natural avalanche activity has slowed down, the past few days have produced reports of wind slabs reacting to ski cutting and to explosives in the Fernie area. Sizes ranged from 1-2 and results have been focused on northeast to northwest aspects.There were reports of several size 2 explosives triggered avalanches on Sunday as well. These were reportedly failing on our mid-January weak layer.Many large storm slab avalanches were triggered naturally, by skiers, and by explosives on Saturday. The avalanches likely released at the base of the storm snow as well as on our mid-January weak layer.

Snowpack Summary

Around 60 mm of precipitation fell last Friday. Above 1600 m, this produced 30-40 cm of new snow which has since been redistributed by strong winds from both north and south. It may sit on weak and feathery surface hoar crystals in shaded and sheltered areas. Below 1600 m, the precipitation fell mainly as rain and formed a new melt-freeze crust on the surface.Above 1600 metres, the mid-January layer of surface hoar and/or crust is now buried around 40 to 60 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m. The melt-freeze crust is found on south aspects at all elevations. Slabs that exist above a combination of surface hoar and crust are likely to be particularly reactive.The remainder of the snowpack is generally well-settled. Thin snowpack areas, such as in the east of the region, may hold weak and sugary faceted grains near the base of the snowpack.

Problems

Persistent Slabs

An icon showing Persistent Slabs
The recent storm brought a critical load to a persistent weak layer now buried 30-70 cm deep. This layer consists of surface hoar preserved in shaded, sheltered areas between 1600-1900 m. It may coexist with a crusty sliding surface on south aspects.
Watch for signs of instability such as whumpfing or cracking. Especially at treeline and below.Choose simple terrain and low-consequence slopes in areas where buried surface hoar may be preservedIncrease caution around open features from 1600-1900 m, such as cutblocks, gullies, and cutbanks.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1.5 - 2.5

Wind Slabs

An icon showing Wind Slabs
Recent snow above 1600 m has been redistributed by southwest winds that switched to northeast. The touchiest deposits will be in the lee of wind-exposed terrain features, particularly near ridges.
Use caution around recently wind-loaded features, especially near ridge crests and in steep terrain.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 7th, 2019 2:00PM