Avalanche Forecast
Regions: Olympics.
New storm slab and wind slab are likely with new wind slab mainly forming on lee slopes ranging from N-SE facing.
Detailed Forecast
Continued cool weather with snow showers and moderate winds overnight should build further possible shallow storm slabs. A brief decrease is expected early Tuesday ahead of another approaching Pacific frontal system. The next system moves into the Olympics midday Tuesday with renewed snow and light to moderate westerly winds. This should begin to build new areas of wind slab on lee slopes below ridges and create some isolated storm slabs.
Dangerous avalanche conditions are expected in the above and near treeline bands Tuesday.
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 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. Over the past four days Hurricane Ridge has received 30 inches of snow as of Monday morning.Â
NWAC pro observer, Matt Schonwald and an NPS ranger travelled extensively Friday around Hurricane Ridge testing the recent storm snow. As of Monday morning, Dec. 21, the Hurricane Ridge study plot had a snow depth of 5 feet! From observations last Friday, about 5500 feet the December 9 crust was buried about 1.5-2 feet and now is likely another foot or more down.Â
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 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.
The most recent snow over the past few days has fallen at very cool and even temperatures and without significant winds.
The main avalanche problem in the Hurricane Ridge area remains wind slabs, on a variety of aspects near ridges and cornices which were noted in observations last week.
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