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Avalanche Forecast

Archived

Jan 12th, 2016–Jan 13th, 2016

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

The avalanche danger should remain elevated in the morning with a slow decreasing trend through the afternoon as storm instabilities begin to stabilize. Evaluate wind loaded slopes carefully and choose more moderately angled slopes to minimize storm related avalanche problems.

Detailed Forecast

Light to moderate rain and snow should taper to light showers on Wednesday and along with a cooling trend that begins Tuesday night and continues through Wednesday.

Stay off steeper slopes and allow storm instabilities time to settle. Look for wind slab mainly on lee 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 stabilized so our focus will be on the upper snowpack.

NWAC pro-observer Matt Schonwald was at Hurricane on Friday and generally found a right side up and stable snowpack. Older wind slab was limited to 15-30 cm pockets near ridges and tests indicated little propagation. Matt also observed surface hoar primarily on sheltered north to 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.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). 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.