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Archived

Avalanche Forecast

Feb 19th, 2018–Feb 20th, 2018
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
2: Moderate
The avalanche danger rating below treeline will be moderate
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: Northwest Coastal.

Strong outflow winds have created wind slabs that should be easy to trigger.  Watch out on solar aspects where the sun could weaken the snow surface.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TUESDAY: Sunny, light to moderate northerly winds, alpine temperature near -9 C, freezing level below valley bottom.WEDNESDAY: Mostly sunny, moderate northerly winds, alpine temperature near -6 C, freezing level below valley bottom.THURSDAY: Partly cloudy, light to moderate westerly winds, alpine temperature -5 C, freezing level below valley bottom.

Avalanche Summary

Many small to large (size 1 to 3.5) wind slabs were reported on both Saturday and Sunday in lee features and cross-loaded terrain on southerly to easterly slopes. The avalanches were triggered naturally and by skiers.Avalanche activity may slow down with a period of cold, clear weather expected to persist well into the week, unless the sun is powerful enough to warm the snow surface. 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

Strong northeast outflow winds have redistributed the 40-60 cm of recent storm snow. The winds have produced touchy wind slabs in lee and cross-loaded features at all elevations (as observed in this post and this one).  The recent winds have also caused cornices to grow in size.  The wind slabs sit on a wide variety of surfaces, including wind-scoured and old wind slabs at higher elevations, a sun crust on steep solar aspects, and facets and surface hoar in sheltered locations at treeline and below treeline elevations. The surface hoar and facet layers are found around 20 to 40 cm deep as well as 60 to 110 cm deep, generally at treeline and below treeline elevations.  Thin spot triggering is the primary concern for the deeper layer.

Avalanche Problems

Wind Slabs

Strong outflow winds have produced stiff and touchy wind slabs in lee and cross-loaded features, with reports of wind slabs reaching into below treeline. These slabs will likely be reactive to human triggers.
Use ridges or ribs to avoid pockets of wind-loaded snow.Be cautious as you transition into wind-affected terrain; avoid lee and cross-loaded features.Look for signs of instability: whumpfing, hollow sounds, shooting cracks, and recent avalanches.

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

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 3