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Avalanche Forecast

Archived

Dec 10th, 2015–Dec 11th, 2015

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

Regions

Mt Hood.

New storm slab will be the primary avalanche problem Friday due to potentially unstable storm layers. Lingering wind slab from Thursday and Thursday night on lee N through SE slopes will be a secondary avalanche problem near and above treeline. Use extra caution if traveling into the above treeline zone (alpine) as there have not been any recent observations from this elevation band. 

Detailed Forecast

Showers should diminish overnight, but a new round of snow should begin by late morning as the parent upper low asscoiated with Thursday's frontal system moves into northern Oregon.  Snow should become moderate in the afternoon with shifting winds as the low tracks to the SW of Mt. Hood. 

New storm slab will be the primary avalanche problem Friday due to potentially unstable storm layers. Lingering wind slab from Thursday and Thursday night on lee N through SE slopes will be a secondary avalanche problem near and above treeline. 

Use extra caution if traveling into the above treeline zone (alpine) as there have not been any recent observations from this elevation band. 

Snowpack Discussion

Over the last 4 days,  9 - 12 inches of water has fallen at the Meadows and Timberline NWAC stations. Unfortunately for elevations below 7000', the large majority was in liquid form!  8-12" of new snow has fallen since the switch back to snow Wednesday morning with light to moderate westerly transport winds. 

Avalanche and Snowpack Observations

The Mt Hood Pro Patrol on Wednesday and Thursday reported a generally stable and draining snowpack with wet grains to the ground. The snowpack depth dramatically increases with elevation, with Meadows patrol reporting almost a meter at 6200 ft. New wind slab was developing near and above treeline Thursday on lee easterly slopes, but was generally not found to be reactive with ski cuts or in snowpack tests. Below treeline should still contain ample terrain anchors, but above 5000' there is enough snow to allow small avalanches in specific areas.  No recent observations have been received for the bulk of the above treeline zone due to weather and visibility restrictions. 

Problems

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.

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.