Avalanche Forecast
Issued: Dec 26th, 2013 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Be aware of increasing danger in the afternoon - especially if new wind and storm slab develop quicker than forecast.
Summary
Detailed Forecast
Mild temperatures should continue overnight into Friday morning. An approaching frontal system should spread light to moderate rain and snow to the Olympics Friday morning. Snow levels should start out rather moderate...and begin to lower later in the afternoon.
New snow may cause shallow storm slabs near and above treeline by the end of Friday. Moderate ridgetop winds from the SW may develop new wind slab in the near and above treeline zone on the usual 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. The 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
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, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 27th, 2013 10:00AM
