Avalanche Forecast
Regions: Olympics.
Dangerous avalanche conditions are expected in the above and near treeline at Hurricane on Sunday with careful snowpack evaluation and cautious route finding essential.
Detailed Forecast
The next strong cool cold front will cross the Northwest Saturday night and Sunday morning. This will renew moderate to heavy snow in the Olympics Saturday night and Sunday morning with a minor warming trend but the snow level will stay low. It looks like the heaviest snow will shift to Oregon Sunday.
Rapid loading will cause new storm and wind slab will build Saturday night and Sunday. Natural storm and wind slab should be possible and triggered storm and wind slab should be likely during the main part of the storm Sunday morning in the above treeline and near treeline. But these conditions could easily last all day Sunday.
Give large cornices a wide margin and watch for areas of recent wind slab deposits. Terrain anchors are still causing significant anchoring at the lowest elevations.
Snowpack Discussion
A major rain event was seen December 7-8th. This caused a crust and wet snow through the snowpack at Hurricane Ridge.
A series of cool storms since then has deposited storm snow at relatively low freezing levels. There has been about a foot of snowfall at Hurricane the past 2-3 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 bring some more stabilizing on Saturday.
In the higher elevations, above tree line, strong winds recently have scoured much of the snow from a wide variety of exposed slopes, leaving much exposed rock and vegetation.Â
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