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Avalanche Forecast

Archived

Jan 30th, 2016–Jan 31st, 2016

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

Regions

Mt Hood.

On Mt Hood Saturday, the main problem has now shifted to new snow instabilities, above the new rain crust. New areas of wind slab on lee wind exposed terrain, near and above treeline. Wind slabs may have formed on a variety of aspects due to highly variable wind directions. Watch for new cornices near ridges. 

Detailed Forecast

Cool weather with light snow showers and moderate westerly winds Saturday should allow for an overall slowly decreasing danger. Weak lower density snow that may exist above the new crust will slowly settle, but remain reactive to human triggers Saturday. 

The greatest avalanche problem should be sensitive wind slabs on lee slopes, mainly NW-N-SE facing slopes, especially below ridges, near and above treeline. 

Watch for newly formed cornices along ridges as well. These may be sensitive to human triggers.

Below treeline, watch for any wind affected snow on exposed terrain features such as cross loaded ribs and larger open slopes.

Snowpack Discussion

Very mild, above freezing weather Wednesday allowed for wet surface snow conditions in most areas.

Mild weather continued Thursday with heavy rain reaching at least 8000 feet on Mt Hood, caused increasing wet snow conditions. 

Snow levels dropped late Thursday as temperatures lowered some 10 degrees or more through the day. The bond of new snow to crust is reportedly strong in the Mt Hood zone Friday, however weak snow above the crust is making for some sensitive ski triggered wind slabs near treeline on N-E facing the wind loaded terrain. No observations were received above treeline due to storm conditions. 

Below treeline, shallow new snow was not reactive overlying the new crust. 

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.