Avalanche Forecast
Regions: Stevens Pass.
Use caution on slopes 35 degrees and steeper and where recent wind drifts have formed at upper elevations. Steer around loaded wind pillows on leeward terrain features near and above treeline. In the past week, storms brought significant snowfall and rain adding stress and new layers to the snow on the ground.
Discussion
Recent avalanches abound! From January 6-7th, a major avalanche cycle occurred in the Stevens Pass area. On Tuesday, brief windows of visibility from Highway 2 yielded upwards of 100 avalanche observations. Seasoned professionals reported numerous avalanches running in places that they hadn't previously observed avalanches. Observers reported that some paths avalanched multiple times in a 24 hour period. Avalanches occurred on all elevations and aspects and were generally large (size D2), 30-50cm deep, and involved recent storm snow. Observers reported a few very large (size D2.5-3) avalanches, originating at upper elevation ridges with deeper crowns that likely formed from wind drifting. On the night of the 6th and morning of the 7th, widespread loose wet avalanches ran up to size D2. Rain fell to at least 5,000ft. on Tuesday.Â
Snowpack Discussion
New Regional Synopsis coming soon. We update the Regional Synopsis every Thursday at 6 pm.
Avalanche Problems
Wind Slabs
Northwest wind has formed fresh drifts on leeward sides of ridges at the middle and upper elevations in the past 24 hours. There are also slightly older wind slabs from January 6th and 7th. Many leeward start zones have deep crowns from avalanches earlier in the week. Avoid deeply drifted features and leeward start zones. Even slopes that have avalanched once could slide again. The most dangerous slopes are at the highest elevations.
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: Likely
Expected Size: 1 - 2
Storm Slabs
You may be still able to trigger avalanches where recent snow has accumulated in the past 24 hours or where you find lingering storm layers from the past couple of days. Use caution on steep, convex slopes and unsupported features. You can find an interface of stiffer snow sitting on softer storm snow about 2-3 feet below the snow surface. Use small test slopes and snowpack tests to look for recent storm layers in the top 2 feet of the snowpack.
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.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1