Avalanche Forecast
Regions: Cascades - North East.
Significant new snow and strong winds over the last several days continue to warrant patience and conservative terrain use. The snowpack is slowing gaining strength, but caution should be taken before stepping into larger terrain.
Detailed Forecast
Cool and clear weather will continue to allow the upper snowpack to strengthen.
Wind slabs formed on Saturday will continue to be a problem Sunday. Look for areas of recently wind transported snow such as uneven snow surfaces, fresh cornices and snow drifts. Identify and avoid areas of wind loaded snow. Recent strong winds may have loaded slopes well below ridge crest. Pay attention to exposed terrain features even below tree line where wind slabs may have formed.
Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.
While storm slabs are gaining strength, the amount of recent snow warrants caution before stepping into larger terrain. Time and patience will allow these layers to heal and the hazard to fall.
Sunshine on Sunday may produce small loose wet avalanches on steep sunny slopes especially near rock outcrops. Pay attention to new roller balls as these are a sign that loose wet avalanches could occur.
Despite recent snow, early season conditions still exist. Pay particular attention to open creeks that have not filled in for the season.
Snowpack Discussion
Saturday afternoon brings a close to a very active weather pattern.
Windy conditions Saturday redistributed much of the recent storm snow forming sensitive wind slabs on a variety of aspects.
In general 1 to 1.5 feet of new snow fell across the eastern slopes of the Cascades between Thursday and Saturday. Fluctuating temperatures during the storms created several layers within the new snow. Mild temperatures have allowed these instabilities to begin to gain strength.
Snow depth decreases substantially the further east of the Cascade crest one travels. In many areas below treeline, there is not enough snow to present an avalanche danger.Â
Observations:
North:
The NCMG were in the Washington Pass area both Friday and Saturday. By Saturday, cooling and settlement allowed for a favorable stability trend. The sensitive storm slab layers and avalanches seen Friday were rapidly gaining strength and becoming less likely to trigger.Â
Central:
Mission Ridge Pro Patrol reported very sensitive wind slabs observed around the area Saturday. A natural avalanche cycle was observed from Friday night. Avalanche control work within the ski area Saturday produces 1-4 ft wind slab avalanches.
On Friday, a public skier triggered a 16-18†wind slab in closed terrain on a NE aspect at approximately 6000’. The skier was not caught nor injured.
South:
No recent observations
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1