Avalanche Forecast

Issued: Feb 17th, 2019 4:47PM

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

Avalanche Canada shorton, Avalanche Canada

Triggering slab avalanches remains possible at all elevations and aspects. Carefully watch for signs of instability such as whumpfs and cracking.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SUNDAY NIGHT: Clearing skies overnight, moderate northwest wind, alpine temperatures drop to -18 C.MONDAY: Mix of sun and cloud, moderate northwest wind, alpine high temperatures around -13 C.TUESDAY: Cloudy with isolated flurries and trace accumulations, moderate to strong northwest wind, alpine high temperatures around -13 C.WEDNESDAY: Cloudy with isolated flurries, light northeast wind, alpine high temperatures around -10 C.

Avalanche Summary

Numerous skier triggered slab avalanches have been reported daily since Tuesday. Although most avalanches have been small (size 1-1.5), they have shown impressive propagation. See these examples from recent MIN reports here and here. Preliminary reports from Sunday indicate freshly wind loaded features were reactive to skier triggering, with a few size 1.5 avalanches reported on a variety of aspects. A persistent slab avalanche was remotely triggered slab on a east aspect at 1850 m. It failed on a 30 cm deep surface hoar layer. On Saturday, a few small (size 1-1.5) slab avalanches were triggered by skiers on convex terrain, especially on south aspects. On Thursday, strong wind formed fresh wind slabs that produced several size 1-2 natural avalanches. The wind slabs were also very reactive to human triggering and produced two large (size 2) skier-triggered slab avalanches (with  80 cm thick crowns).

Snowpack Summary

Surface snow consists of a mix of low density snow and hard wind affected surfaces. 20 to 40 cm of snow from the past few days is gradually settling, and in some areas has shown signs of becoming reactive above above a surface hoar and crust layer that was buried on February 7th. This layer is suspect at all elevations, particularly on wind loaded slopes and on steep south-facing terrain.Two other surface hoar layers are buried 50 to 80 cm deep the snowpack (referred to as the February 1st and mid-January layers). Although they have not been reactive recently, they are still being monitored by professionals. These layers are most prevalent below treeline on shady aspects. The lower snowpack is well settled.

Problems

Persistent Slabs

An icon showing Persistent Slabs
It remains possible to trigger an avalanche on one of the surface hoar or crust layers buried 30 to 80 cm deep. These layers are most prominent at treeline and below.
Caution around sheltered open areas at treeline and below including cutblocks, gulleys, and glades.Surface hoar distribution is highly variable. Avoid generalizing your observations.Use caution on open slopes and convex rolls

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Wind Slabs

An icon showing Wind Slabs
Wind slabs can be found on a variety of aspects and at all elevations.
If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Use caution in freshly wind-loaded features, especially near ridge crests.Wind from a variety of directions has formed wind slabs in unusual locations.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Feb 18th, 2019 2:00PM