Avalanche Forecast
Regions: Olympics.
New storm slab and wind slab are likely depending a lot on the changeable weather pattern on Monday.
Detailed Forecast
A strong low pressure system will move west to east across Washington on Monday. There should be a big difference in the weather and avalanche conditions between the Olympics and Cascades with the strongest winds and heaviest snowfall in the south Cascades. Right now it looks like the main effects of the low may reach as far north as the central Cascades. But a different track of the low could bring much different than expected weather and avalanche conditions on Monday so the forecast is somewhat uncertain.
Light to moderate winds and snow are expected in the Olympics on Monday. New storm slab and wind slab are likely depending a lot on the changeable weather pattern. Dangerous avalanche conditions are expected in the above and near treeline on Monday.
Remember to give cornices a wide margin. Also above tree line strong winds recently have scoured snow from exposed slopes leaving exposed rock and vegetation. Terrain anchors are still causing significant anchoring at the lowest elevations.
Snowpack Discussion
A series of cool storms has deposited increasing storm snow at relatively low freezing levels since early December. Some rain probably made it up to Hurricane on December 17th. There has been about 1-1.5 feet of snowfall at Hurricane the past 2-4 days.
NWAC pro observer Matt Schonwald and a NPS ranger travelled extensively Friday around Hurricane Ridge testing the recent storm snow. At around 5500 feet the snow depth is about 4-5 feet with the December 9 crust buried about 1.5-2 feet from the recent storm snow. The snowpack in the Hurricane Ridge area was mostly unconsolidated low density surface snow with a gradually increasing density down to the well bonded crust, a very good profile. 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.
The general break in the weather should have brought some more stabilizing on Saturday. The ranger reported 8 inches of new snow on Sunday.
Avalanche Problems
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: Likely
Expected Size: 1 - 1
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