Avalanche Forecast
Regions: Olympics.
New or recent wind slab should be most likely on lee north to southeast facing slopes. Storm slab or loose dry avalanches in non-wind affected terrain mean you need to use extra caution around terrain traps.
Detailed Forecast
A cool upper trough will continue to sink south over the Pacific Northwest on Thursday. West winds should begin to decrease Thursday initially in the Olympics and north Cascades. Snow showers may another few inches to Hurricane.
Dangerous avalanche conditions should persist Thursday especially in the near and above treeline zones where new or recent wind slab be likely. Wind or storm avalanches should remain within recent storm layers but could move fast. Watch for evidence of wind deposited snow or pillows. Test for inverted strong over weak storm snow and give cornices a wide margin.
Loose dry avalanches in non-wind affected terrain may be difficult to manage on steep slopes. Even a small loose dry avalanche could have unintended consequences such as knocking you off your feet and into a terrain trap.
Terrain anchors are still causing anchoring at the lowest elevations, but less and less with every storm passage!
Snowpack Discussion
A series of cool storms has deposited increasing storm snow at relatively low freezing levels since early December. The last rain event occurred to the Hurricane Ridge elevation on December 17th. By Thursday morning Hurricane Ridge will have received about 3 feet of snow in the past few days.
NWAC pro observer, Matt Schonwald and an NPS ranger traveled extensively Friday around Hurricane Ridge testing the recent storm snow. The snow pack was mostly unconsolidated low density surface snow with a gradually increasing density down to the well bonded crust, a very good profile as of late last week. No slab character was noted in the upper snowpack during testing. Only isolated wind slabs were noted with no releases. Extensive cornices were noted on north to northeast sides of ridges. Skiing was very good.
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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, Treeline.
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, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Loose Dry
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose Dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose Dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Loose Dry avalanche with the characteristic point initiation and fan shape.
Loose dry avalanches exist throughout the terrain, release at or below the trigger point, and can run in densely-treed areas. Avoid very steep slopes and terrain traps such as cliffs, gullies, or tree wells.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1