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Avalanche Forecast

Archived

Nov 26th, 2017–Nov 27th, 2017

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

Regions

Mt Hood.

As the snowpack refreezes, there is still a low chance for glide avalanches near and below treeline on steep unsupported terrain features. Much of the below treeline elevation band does not have enough snow cover to support an avalanche hazard. Isolated and shallow pockets of storm or wind slab may exist near and above treeline. Watch for non-avalanche related hazards such as open creeks and barely buried rocks and trees. 

Detailed Forecast

A fresh 4-8" of snow is forecast Sunday night through Monday morning. Light snow showers are expected for the remainder of Monday. 

The snowpack will begin to refreeze Sunday night and Monday with cooler weather. There is still a low chance for glide avalanches near and below treeline on steep unsupported terrain features that did not release during the recent heavy rains. Much of the below treeline elevation band does not have enough snow cover to support an avalanche hazard. Otherwise shallow isolated pockets of storm or wind slab may exist near and above treeline. The Moderate hazard will be maintained near and above treeline in part due to the lack of direct observations over the last few days. 

Watch for the numerous travel hazards such as open creeks, barely buried rocks and trees, and glide cracks, creating poor and challenging travel conditions, especially below treeline. 

Remember that closed ski areas without avalanche mitigation are equivalent to backcountry terrain!  

 

Snowpack Discussion

Avalanche and Weather Summary

New resources within your Avalanche Forecast this season! 

The Mountain Weather tab will take you to the most recently issued Mountain Weather Forecast. The Observations & Weather Data tab will allow an easy view of the various weather station graphs within your zone of interest and provide easy access to the most recent avalanche and snowpack observations. 

The great start to the 2017/18 PNW Winter took a giant step backwards over the last week. During an extended period of warmth and wet weather in the days leading into Thanksgiving, an initial round of wet snow and glide avalanches occurred, especially on steep unsupported slopes and rock faces. Another round of rain Saturday night through mid-day Sunday likely did not cause widespread wet snow avalanches on an already beat up and saturated snowpack. This warm, wet and windy period melted significant snow with total snow depths decreasing by 50% or more from their mid-November peak depths at many NWAC stations including Mt. Hood. This has allowed much of the previously well snow-covered terrain to open with many creeks and snow bridges re-appearing, especially near and below treeline. 

Rain had changed to snow Sunday afternoon with further cooling and generally light snow accumulations expected overnight.

Observations

No weekend observations due the wet weather, numerous ski area closures and lack of snow in WSDOT avalanche paths. 

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.

Glide Cracks

Glide avalanches occur when water lubricates the interface between the snowpack and the ground. These avalanches are difficult to predict and best managed by avoiding terrain below glide cracks.