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Avalanche Forecast

Archived

Feb 14th, 2018–Feb 15th, 2018

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

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Identify and avoid areas of wind deposition such as below cornices, on snow drifts, or near blowing snow, where you are likely to trigger an avalanche. The recent storm snow is poorly bonded to the old snow surface. Stay off of steep unsupported and/or convex slopes where you are more likely to trigger a storm slabs as the new snow settles.

Detailed Forecast

Avalanches have been triggered in the last 24 hours and you will still be able to trigger avalanche Thursday.

Winds have drifted snow near and above treeline forming wind slabs on lee slopes near ridgeline. Use visual clues to identify and avoid wind deposited snow such as blowing snow, fresh cornices, snow drifts, and variable snow surfaces with cracking.

Storm snow will continue to settle and consolidate Thursday making it possible for you to trigger storm slabs in sheltered area. Stay off steep unsupported and/or convex slopes where you are more likely to trigger a slab avalanche. Some of these storm slabs may fail on old weak surface snow such as near surface facets observed throughout the forecast region.

The new snow has bonded poorly to the old snow surface. Although it is not listed as a problem you may be able to trigger small loose dry avalanches in steep terrain. Be careful traveling on slopes above terrain where even a small avalanche can have large consequences.

Glide cracks and other holes in the snowpack formed during the first week of February. These openings are now covered by a thin layer of snow and pose a hazard to backcountry travelers. Be cautious when traveling near depressions in the snowpack and maintain communication with your travel partners.

Snowpack Discussion

A snowboarder triggered avalanche was reported on the north side of Chair Peak in the Cache Couloir (Snoqualmie Pass). The avalanche occurred on a steep NE facing slope at 4500 feet. The rider was not caught and no injuries were sustained.

Wednesday 6-12 inches of new 5-10% density snow fell across the west slopes of the Cascades. Highest snow totals were seen at Paradise on Mt Rainier. Light to moderate west southwest winds transported the storm snow and formed wind slabs on lee slopes. In sheltered areas the new snow was poorly bonded to the old snow surfaces. Several loose dry avalanches were reported running far and fast.

Storm snow fell on a variety of old snow surfaces including melt-freeze crust on southerly aspects, uneven wind affected snow above treeline, and weak near surface facets on shaded slopes. Unstable snow will be limited to the new snow and its bond to the old snow surface. Below the old snow surface a strong consolidated snowpack exists in most locations. There are no significant layers of concern below the most recent crust layer.

Observations

Avalanche professionals in the Stevens Pass area Wednesday reported loose snow surface conditions. The new snow was bonding poorly to the old snow surfaces creating Loose Dry avalanche conditions. Near treeline winds had drifted snow forming shallow wind slabs on lee slopes.

NWAC staff in the field Saturday through Wednesday reported a variety of snow surfaces in every region including firm surface crust, wind effected snow, and near surface facets. Observations continue to demonstrate a strong snowpack below the most recent crust layer.

Over the weekend, numerous glide cracks and openings in the snowpack were present and created a non-avalanche travel hazard.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.