Avalanche Forecast

Issued: Feb 13th, 2019 4:33PM

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

Avalanche Canada cgarritty, Avalanche Canada

Dangerous avalanche conditions are widespread. Thick storm slabs already blanket higher elevations, with lower elevations an increasing concern as new snow settles and forms slabs over weak layers at the old surface and deeper in the snowpack.

Summary

Confidence

High -

Weather Forecast

Wednesday night: Cloudy with clear periods. Light northwest winds.Thursday: Mainly sunny with cloud increasing and flurries beginning in the evening. Light southeast winds. Alpine high temperatures around -10.Friday: Cloudy with increasing flurries bringing about 10 cm of new snow by end of day, continuing overnight. Light southwest winds. Alpine high temperatures around -6.Saturday: Cloudy with continuing periods of snow bringing 10-15 cm of new snow by end of day, with new snow totals around 30 cm, flurries easing overnight. Light variable winds. Alpine high temperatures around -9.

Avalanche Summary

Improved visibility on Wednesday allowed for observations of numerous large (size 2-3) natural storm slabs on north to northeast-facing features in the Fernie area. Subsequent explosives control in the same area also yielded storm slabs up to size 2.5, mainly on northeast aspects. Ski cutting continued to produce storm slab and loose dry releases to size 1.5.Observations from Tuesday showed widespread loose dry and storm slab releases reaching size 1.5. These occurred naturally as well as with ski cutting and skier traffic. A report from the Flathead on Monday described continued observations of large whumpfs at 1700-1800 metres. This can be attributed to collapsing of the large, weak, January 17 layer of surface hoar. Collapses of this type on a sufficiently large and steep slopes can be expected to produce persistent slab releases.Another small (size 1) persistent slab was triggered by a skier in the western Flathead on Saturday. The slab was 40 cm deep and released from a northeast aspect at 1800 metres in an area that had not seen recent traffic. Several other small persistent slabs were triggered with ski cuts in the same area.

Snowpack Summary

30 to upwards of 50 cm of new snow has buried a variable surface of older wind-affected snow at wind-exposed treeline and alpine elevations, a new weak layer of feathery surface hoar in protected areas at lower elevations, and a thick melt-freeze crust below 1600 metres. Below the new snow, another 20-30 cm of older storm snow may sit on weak and feathery surface hoar crystals in shaded and sheltered areas.Above 1600 metres, the mid-January layer of surface hoar and/or crust is now buried around 70 to 90 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. This layer was the subject of a recent Special Public Avalanche Warning and remains a serious concern as it adjusts to the load of new snow above it.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

Storm Slabs

An icon showing Storm Slabs
From 30 cm to upwards of 50 cm of new snow fell over the region by Wednesday morning. Dangerous avalanche conditions with a reactive storm slab problem is the result. Human triggering potential will persist as natural avalanche activity tapers off.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.Expect instability in the new snow. It will need several days to settle and stabilize.Minimize your exposure to areas with overhead hazard.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

Loose Dry

An icon showing Loose Dry
Loose snow avalanches remain concern for Thursday with upwards of 50 cm of new low density snow in the region. Terrain traps and careless group management can greatly increase the consequences of loose dry avalanches.
Sluffs will be easy to trigger in steep terrain that is sheltered from the windBe aware of party members below you that may be exposed to your sluffs.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Likely - Very Likely

Expected Size

1 - 1.5

Persistent Slabs

An icon showing Persistent Slabs
Snowfall has increased the load on a persistent weak layer now buried around 60-90 cm deep. This layer consists of surface hoar preserved in shaded, sheltered areas between 1600-2000 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 where buried surface hoar may be preserved.Increase caution around open features from 1600-2000 m, such as cutblocks, gullies, and cutbanks.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 14th, 2019 2:00PM

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