Avalanche Forecast
Issued: Dec 25th, 2013 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Wind Slabs.
NWAC,
Northwest Avalanche Center
Summary
Detailed Forecast
Mostly sunny days and fair nights, generally light winds and mild temperatures are expected through Thursday. This should again allow for some surface snow melt on sun exposed terrain. Some shallow wet snow conditions may develop by late morning or afternoon on steep facing solar aspects where there is enough snow to slide. Older wind slab may still be sensitive on lee NW thru E aspects.
Snowpack Discussion
The last significant snow occurred in early December. Either strong high pressure or systems with high freezing levels have limited the snow accumulations in the Olympics and specifically at Hurricane Ridge where the total snowdepth remains a meager 12 inches. NWAC weather station at Hurricane has recorded less than 2 inches of water through December.
The overall shallow snowpack is limiting the avalanche danger, especially near tree line and below tree line where significant terrain and vegetative anchors remain. Field observations to Klahhane Ridge Sunday indicated that the lack of snow indeed is limiting the danger on most slopes. On north facing slopes below the ridge there was evidence of wind slab or wind drifts ranged to over 1 meter but most areas have mostly 30-75 cm (1-2+ ft) of snow depth. Rain to high elevations and lack of recent snow is maintaining mostly stable conditions with surface crusts or shallow wind drifts over crust layers.
View from Klahhane Ridge south facing slope, Olympics 12-22-2013, K. Reid
View looking east along Klahhane Ridge, Olympics 12-22-2013, K. Reid
Watch for areas where a locally deeper snow pack may exist. The most likely areas to find any unstable conditions would be on steep generally northerly facing terrain below ridges above tree line. In these areas, some wind slab may be present.
Problems
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
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, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Dec 26th, 2013 10:00AM
