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Avalanche Forecast

Archived

Dec 29th, 2015–Dec 30th, 2015

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.

Regions

Mt Hood.

Wind slabs should be found on a variety of aspects, mainly near and above treeline. Remember MODERATE danger means human triggered avalanches are possible. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees. 

Detailed Forecast

Wind slabs are becoming more isolated and difficult to trigger, and that should be the case Wednesday. However, wind slabs may still be encountered on maily north to southeast aspects, near and above tree line. NW winds may redistribute recent snowfall to lee SE slopes above treeline Wednesday. Any triggered wind slab avalanches should be relatively small and remain within recent storm layers. Test for inverted strong over weak storm snow and give cornices a wide margin.

Dry loose avalanches have been removed as an avalanche problem from the forecast as recent deep snow continues to settle making these less likely.

There have been snow immersion fatalities in tree wells already this season at Snoqualmie and in Canada. Recent unconsolidated storm snow is still very deep in places with possible large tree wells lurking, so stick near your partner in the trees and maintain visual contact.  

Snowpack Discussion

For the week ending on Dec. 24th, a snowy and cool storm cycle brought 6-7 feet of snowfall to Mt. Hood NWAC stations. A weak passing front deposited 4-5 inches of new snow Tuesday at cool temperatures and light winds. This should add to the generally favorable snowpack profile of light surface snow with gradually increasing density snow with depth (right side up!). Over the last several days only light snowfall has allowed the snowpack to gradually settle, providing some great skiing and riding!  

In non-wind affected areas, the upper snowpack should generally be right side up with increasing hardness with depth. Moderate S-SW transport winds with Sunday's frontal system may have built shallow new wind slab on N through E aspects. 

The most recent snowpack and avalanche observations include control work with explosives on Christmas by the Mt. Hood Meadows pro-patrol, as they were able to trigger large avalanches on specific wind loaded slopes near treeline that stepped down to the Dec.17th rain crust. However, these results were not repeatable on other slopes of similar aspect and elevation with larger explosives.  

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.