Avalanche Forecast

Issued: Feb 20th, 2018 3:55PM

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

Avalanche Canada mconlan, Avalanche Canada

Wind slabs linger at higher elevations -- best to stick to sheltered terrain. Watch out on solar aspects where the sun could weaken the snow surface.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

WEDNESDAY: Cloudy early morning with trace snowfall then mostly sunny, moderate to strong northerly winds, alpine temperature near -12 C, freezing level below valley bottom.THURSDAY: Partly cloudy with increasing cloudiness, light to moderate westerly winds, alpine temperature -7 C, freezing level below valley bottom.FRIDAY: Cloudy with early-morning snowfall, accumulation 2-5 cm, light to moderate westerly winds, alpine temperature near -8 C, freezing level near 400 m.

Avalanche Summary

On Monday, a small wind slab was skier triggered that scoured down to the basal sugary faceted snow in a thin snowpack area, around 60 cm in thickness. This occurred on a southerly aspect around 2000 m in elevation.On Saturday and Sunday, many small to large (size 1 to 3.5) wind slabs were reported in lee features and cross-loaded terrain on southerly to easterly slopes. The avalanches were triggered naturally and by skiers.Avalanche activity may increase with warmer air temperatures and if clear skies prevail. Watch for steep sunny slopes due to the suns influence, lee features for reactive wind slabs, and be extra cautious near thin spots and shallow snow pack areas where triggering a deeper weak layer is more likely.

Snowpack Summary

Northeasterly winds have created stiff wind slabs on leeward slopes and scoured wind-exposed slopes. The cold temperatures are helping to break down these wind slabs, but they will likely remain reactive to light and heavy loads where preserved.Deeper in the snowpack, two layers of crust and/or weak surface hoar are 20 to 40 cm deep and 60 to 100 cm deep. The deeper crust exists well into the alpine and the surface hoar can be found in sheltered areas in lower alpine and tree line elevations. Snowpack tests have produced hard, sudden results on weak, sugary snow crystals associated with this deeper crust in the Smithers area, suggesting that it is a layer of concern.

Problems

Wind Slabs

An icon showing Wind Slabs
Strong winds produced stiff wind slabs in lee and cross-loaded features. The slabs have been described as highly variable. They may be reactive to human triggers and could become touchier with solar warming.
Be cautious as you transition into wind-affected terrain; avoid lee and cross-loaded featuresUse ridges or ribs to avoid pockets of wind-loaded snow.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 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
Several weak layers are lurking in our snowpack. They will be more easily triggered where the snowpack is shallow.
Be aware of the potential for wide propagation.Minimize overhead exposure, as avalanches could run for long distances.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 3.5

Valid until: Feb 21st, 2018 2:00PM

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