Avalanche Forecast
Regions: Olympics.
The avalanche danger should improve through the afternoon as storm and wind slab instabilities further stabilize. Evaluate wind loaded slopes carefully and choose more moderately angled slopes to minimize storm related avalanche problems.
Detailed Forecast
The Olympics will be between storms Thursday and the next system should move inland to affect the regions further south towards the Oregon/California border later Thursday and Thursday night. Only light amounts of new snow are expected late Thursday and Thursday night, allowing for a slow decrease in danger through the day Thursday.Â
Remain cautious in steeper terrain giving storm instabilities time to settle. Look for wind slab mainly on lee north and easterly aspects near and above treeline. Watch for signs of firmer wind transported snow that can indicate wind slab layers near and below ridges.
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.
NWAC pro-observer, Matt Schonwald was at Hurricane on Friday and 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.
Shallow amounts of storm snow by Wednesday fell with a cooling trend during the day and with relatively light winds, not causing a significant increase in danger.Â
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: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 1