Avalanche Forecast
Regions: Olympics.
Carefully evaluate steep slopes still showing signs of firmer wind transported snow from early this week. Snowfall should be light by the end of the daylight hours on Friday and not cause a great change in conditions. But use more caution if snowfall is greater than expected.
Detailed Forecast
A weak cold front will move northwest to southeast over the Olympics and Cascades Friday afternoon and night. This should cause increasing northwest winds Friday in most areas. Light rain if any should quickly change to light snow due to a rapid cooling trend. The main light snow should be seen in the Olympics and north Cascades Friday afternoon spreading to the south Cascades Friday evening with little making it to Mt Hood Friday night.
The light amounts of snow in the Olympics and Washington Cascades should not greatly change snow conditions. Any new storm slab should be mainly in the Olympics and in the north Cascades, small and shallow, and will be rated as unlikely.
Watch for lingering wind slab from early in the week where the northeast winds redistributed snow mainly above and near treeline.
Sun crusts are also likely on steep south slopes where sun warmed snow from Thursday refreezes on Friday.
Snowpack Discussion
A storm system hit the Northwest last weekend with strong west to northwest winds. The NWAC site at Hurricane picked up about 12 inches of storm snow with a good cooling trend.
An upper ridge tilted inland on Wednesday and Thursday. Temperatures warmed dramatically at Hurricane. NWAC observer Tyler Reid was at Hurricane Ridge on Wednesday and reported widespread small wet loose avalanches. Snow on north slopes was more wind affected but he rated slab layers as unlikely. A 3 cm thick graupel layer was seen at 10 cm below the surface which could be something to watch on shaded slopes. Conditions should be similar on Thursday.
Graupel layer at Hurricane on Wednesday by Tyler Reid.
At Hurricane where there is significant snow a strong mid and lower snowpack is expected to be preventing deeper instabilities.
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: Unlikely
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