Archived

Avalanche Forecast

Feb 18th, 2018–Feb 19th, 2018

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

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

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

Regions: Northwest Coastal.

Strong outflow winds have created very touchy wind slabs. Be cautious in terrain features where snow has accumulated, as the slabs will likely be easy to trigger.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

MONDAY: Partly cloudy with increasing cloudiness, moderate northwesterly winds, alpine temperature -9 C, freezing level below valley bottom.TUESDAY: Mostly sunny, light to moderate northerly winds, alpine temperature near -8 C, freezing level below valley bottom.WEDNESDAY: Mostly sunny, moderate to strong northerly winds, alpine temperature near -5 C, freezing level below valley bottom.

Avalanche Summary

Many small to large (size 1 to 2) wind slabs were reported on Saturday in steep alpine and cross loaded terrain. They were reported to have released naturally and by skiers due to rapid wind loading from strong northeasterly winds. A small cornice failure was also noted.

Snowpack Summary

Strong northeast outflow winds have redistributed the 40-60 cm of snow that fell since Tuesday. The winds have produced touchy wind slabs in lee and cross-loaded features at all elevations (as observed in this post and this one). This snow sits 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 facets are found around 60 to 110 cm below the surface on all aspects up to elevations of 1400 m.A deeply buried crust/surface hoar layer from mid-January exists in sheltered areas at treeline and below treeline elevations. Thin spot triggering is the primary concern for this layer.

Avalanche Problems

Wind Slabs

Strong to extreme winds have produced stiff and touchy wind slabs in lee and cross-loaded features. These slabs will be reactive to both natural and human triggers.

Be cautious as you transition into wind-affected terrain; avoid lee and cross-loaded features.Use 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: All elevations.

Likelihood: Likely

Expected Size: 1 - 3