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Avalanche Forecast

Apr 15th, 2018–Apr 16th, 2018
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Sea To Sky.

Wind slabs formed early-weekend have been reactive to human traffic. Snowfall on Monday could build new slabs, which may not bond well to variable underlying surfaces.

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

MONDAY: Cloudy with light snowfall, accumulation 5 to 15 cm, light to moderate southeast winds, alpine temperature -5 C, freezing level 1400 m.TUESDAY: Cloudy with light snowfall, accumulation 2 to 5 cm, light west winds, alpine temperature -6 C, freezing level 1300 m.WEDNESDAY: Mostly cloudy, light southwest winds, alpine temperature -7 C, freezing level 1300 m.

Avalanche Summary

On Saturday, wind slabs and cornices were reactive to explosives, producing small avalanches generally in wind-loaded alpine and treeline terrain.

Snowpack Summary

30 to 40 cm of recent snow has been redistributed by strong south winds, forming reactive wind slabs up to 1 m deep in lee terrain features.  Sun, rain, and warm air temperatures on Sunday moistened the snow surface, which will freeze into a melt-freeze crust on all aspects up to at least 1800 m.  Snowfall on Monday will fall on these surfaces.  Ridgelines are heavily corniced and if they fail they could trigger slabs on slopes below.A weak layer consisting of surface hoar, facets, and/or a melt-freeze crust from late March is now buried about 60 to 140 cm. Although this layer is spotty in its distribution and avalanches haven’t been reported on it since early April, professionals are treating it seriously and avoiding terrain because of it.  It is mostly likely to be problematic on west, north, and east aspects between 1900 m and 2250 m.Below this, the snowpack is well-settled and strong.

Avalanche Problems

Wind Slabs

Strong south winds redistributed recent snow.  Slabs up to 1 m thick are found in lee terrain features.  They have been reactive to human and natural triggers.  Watch your overhead exposure, as cornices could trigger slabs on slopes below.
Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.Use ridges or ribs to avoid pockets of wind-loaded snow.Avoid steep slopes when air temperatures are warm or the solar radiation is strong.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2.5

Persistent Slabs

Professionals are still travelling cautiously due to a weak layer buried 60 to 140 cm.  Be particularly cautious around upper treeline and alpine terrain on shady aspects, where this layer is most likely to be a problem.
Avoid steep terrain or areas with a thin or variable snowpack.Be aware of the potential for wide propagation due to the presence of buried weak layers.Pay attention to overhead hazards like cornices, which could trigger persistent slabs.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine, Treeline.

Likelihood: Unlikely - Possible

Expected Size: 2 - 3