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Avalanche Forecast

Archived

Jan 19th, 2015–Jan 20th, 2015

Alpine
Natural avalanches unlikely, human triggered possible.
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.

Regions

Mt Hood.

Watch for locally sensitive wind slabs on lee slopes near and above treeline and sun affects on steeper solar slopes Tuesday afternoon.  

Detailed Forecast

Tuesday should be partly to mostly sunny with a gradual warming trend. Recent shallow storm snow should continue to settle, but sunshine and increasing temperatures in the afternoon may activate loose wet avalanches predominately on steeper southerly slopes. Especially watch above treeline, where more snow is available for entrainment and could funnel you into a terrain trap.  

Also, there may be pockets of sensitive wind slab mainly on N-SE aspects near and above treeline.  

 

Snowpack Discussion

Strong southwest flow carried a warm and wet front across the PNW Saturday night. This front tapped subtropical moisture pushed snow levels pretty high on Mt. Hood resulting in 3.5 - 4.5 inches of rain at NWAC sites. A cooling trend Sunday along with another inch of water ended as 4-5 inches of new snow between 5-6000 feet by Monday morning. 

NWAC observer CJ Svela was at Timberline on Sunday. He found consolidated P and 1F layers in the top meter of the snowpack but no avalanche activity in this area. Mt. Hood pro-patrol reported wind transport Mon AM leading to a thin and soft wind slab above treeline. West winds eased off more quickly than forecast Monday and new wind transport was not likely significant. 

The mid and lower snowpack at Mt Hood should also mainly consist of melt-freeze crusts and stabilized rounded grain layers from warm stretches so far this winter. 

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.