Avalanche Forecast
Regions: Olympics.
Watch for new wind or storm slab layers above treeline Thursday afternoon in the Olympics.
Detailed Forecast
A southwest-northeast oriented front will move slowly to the International border area on Thursday with a series of waves beginning to move along the front. This should cause new snow above treeline and rain near and below treeline over the Olympics and north Cascades Thursday afternoon.
So the main change to watch for will be in the Olympics and northwest Cascades Thursday afternoon. In these areas above treeline watch for new wind and new storm slab to develop if there is more than several inches of new snow by the end of the daylight hours. Less new snow will mean less of an increase in new wind and storm slab avalanche danger Thursday afternoon.
Further snow above treeline and rain near and below treeline should be seen in the Olympics and northwest Cascades Thursday night.
In all areas in the Olympics and west of the crest Thursday watch for previous shallow wind slab on previous lee slopes. Loose wet avalanches should also remain possible especially on solar slopes.
Little snow in the Olympics below treeline should greatly limit the avalanche danger in that area.
Snowpack Discussion
Last weekend another warm and wet system brought a one-two punch to the Pacific Northwest. The initial system Saturday brought mostly rain with a few inches of snow at Hurricane. This was followed by 16-18 inches of new snow Sunday at the NWAC Hurricane Ridge station.Â
A weak front may have caused minor rain or snow at Hurricane on Tuesday.
NWAC observer Tyler Reid toured above Hurricane Ridge on Tuesday and reported about 1-2 feet of wet snow with up to 3 feet in drifts near ridges. There were numerous recent small loose wet avalanches seen on all aspects with a few larger avalanches. Avalanches ran into ares with little or now snow cover.
Loose wet avalanche debris size 2 on Tuesday, March 17th, above the tunnels on road to Hurricane Ridge. Photo by Tyler Reid.
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: North, North East, East, South East.
Elevations: Alpine.
Likelihood: Likely
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: Alpine.
Likelihood: Likely
Expected Size: 1 - 1
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1