Avalanche Forecast

Issued: Feb 5th, 2019 4:54PM

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.

cgarritty, Avalanche Canada

Lizard-Flathead.

Use patterns of wind redistribution visible on the surface to steer you away from pockets of wind slab. Persistent slabs don't offer these kinds of clues unless you trigger one, so raise your guard and choose more simple terrain below 1900 metres.

Summary

Confidence

Moderate -

Weather Forecast

Tuesday night: Cloudy with clear periods. Light variable winds.Wednesday: Sunny. Light northeast winds increasing to moderate in the alpine. Alpine high temperatures around -17.Thursday: A mix of sun and cloud with cloud increasing over the day. Light southwest winds, increasing to moderate or strong northwest in the alpine. Alpine high temperatures around -15.Friday: Mainly cloudy with isolated flurries and a trace of new snow. Light northeast winds. Alpine high temperatures around -20.

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, we had reports of wind slabs reacting to ski cutting and to explosives in the Fernie area on Monday. Sizes ranged from 1.5-2 and results were 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 on Friday with a freezing level at 1600 m. Above 1600 m, the precipitation fell as snow, which has been redistributed by northwest winds. It may sit on weak and feathery surface hoar crystals in shaded and sheltered areas. Below 1600 m, the precipitation fell as rain and froze into a melt-freeze crust.The mid-January layer of surface hoar and/or crust is 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.The remainder of the snowpack is generally well-settled. Thin snowpack areas, such as in the east of the region, may find weak and sugary faceted grains near the base of the snowpack.

Problems

Persistent Slabs

The recent storm snow 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 m and 1900 m. It may coexist with a crust on south aspects.

Be aware of heightened avalanche danger between 1600-1900 metres.Choose simple terrain and low-consequence slopes in areas where buried surface hoar may be preservedWatch for signs of instability such as whumpfing, cracking, or recent avalanches.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Wind Slabs

Recent snow above 1600 m has been redistributed by southwest winds that switched to northeast winds. The touchiest deposits will be in the lee of wind-exposed terrain features, particularly near ridges.

If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Use caution around recently wind-loaded features, especially near ridge crests and in steep terrain.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 6th, 2019 2:00PM