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Avalanche Forecast

Archived

Dec 21st, 2014–Dec 22nd, 2014

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

Mt Hood.

The storm over the region Saturday night and Sunday produced mainly rain for the Mt. Hood area at elevations where avalanche forecasts apply. However, the avalanche danger on the upper volcano will likely be much greater due to heavy snow and strong winds. Travel into the alpine is strongly discouraged.  

Detailed Forecast

The storm over the weekend should be in the rear view mirror by Monday, as high pressure rebuilds.  This should cause light to moderate northwest crest level winds and little if any accumulation of new snow. 

Recent storm and wind slabs should persist at higher elevations, especially above treeline and near ridgetops. Best performing numerous quick test pits or pole tests to determine recent snow conditions. Wet snow conditions should gradually drain Monday at mid and lower elevations. 

Snowpack Discussion

The snowpack on Mt. Hood below 6000' remains relatively shallow and marginal for avalanche formation.  Snowdepths are now 1-2 ft after snowfall Saturday at NWAC stations near tree-line.  We have no recent avalanche activity or observations which, considering the strength of the weekend storm is a good thing!

A very strong storm began affecting the Mt Hood area Friday.  NWAC weather stations have recorded between 5-10" of water equivalent in 48 hours as of Sunday evening!  The majority of this has been in the form of rain, however, above treeline much of the recent precipitation has been snow.  Coupled with winds in excesses of 100 mph, there is no doubt highly varied conditions on Mt Hood presently.

The rain, snow, extreme winds and fluctuating freezing levels have certainly changed the landscape of the snow conditions by Sunday.   Little field information has been available Sunday, however, expect lower to mid elevations to begin slowly freezing and forming a new crust with shallow amounts of new snow being well bonded to the old surface.

Be extremely cautious venturing to higher elevations as deep storm and wind slabs are likely.

 

 

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.