Avalanche Forecast
Regions: Olympics.
Mostly light amounts of new snow Friday are not expected to cause a great change in snow conditions. Adjust your plans if you are out and find more than a few inches of new snow on Friday.
Detailed Forecast
A system will move mainly across Oregon and north California on Thursday night. This system should spread some moderate snow as far north as Mt Hood on Thursday night and Friday morning with way less in the Olympics and Washington Cascades.
Some snow showers should drift north over western Washington on Friday. The snow showers should bring mostly light amounts of new snow in the Olympics and Washington Cascades and are not expected to cause a great change in snow conditions at Hurricane.
Avalanche problems should be mainly from layers formed during the snowfall seen about January 12-14th.
Wind slab from January 12-14th should be possible on ridges and on north to southeast slopes near and above treeline. Watch for signs of hollow snow and firmer wind transported snow.
Storm slab where it might still exist from January 12-14th could linger on more varied aspects but should be becoming unlikely and should be stabilizing.
New wind or storm slab layers would be possible if there is more snow than expected on Friday. Be prepared to adjust your plans if you are out and find more than a few inches of new snow on Friday.
Snowpack Discussion
Deep storm snow that fell during mid-late December is well settled, homogeneous and has stabilized, so the focus on the current avalanche danger will be on the upper snowpack and the most recent storm snow.
Fair weather over the New Year caused extensive surface hoar and near surface faceted snow. This was followed by about 6 inches of snowfall at Hurricane about January 3-6th.
The last observation for Hurricane is from NWAC pro-observer Matt Schonwald at week ago and he generally found a right side up, stable snowpack. Older wind slab was limited to 6-12 inch (15-30 cm) pockets near ridges and tests indicated little propagation. Matt also observed surface hoar primarily on the sheltered north-east slopes. Any lingering surface hoar was likely destroyed by mild temperatures and rain Monday or Tuesday. Strong winds and rain up to at least 5500-6000 feet Tuesday likely caused a loose wet avalanche cycle on steeper slopes near and below treeline.
The latest period of snowfall has been from about January 12-14th with about 5 inches of snowfall at Hurricane. A cooling trend was seen at the tail end yesterday.
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: Possible
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: Unlikely
Expected Size: 1 - 1