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Avalanche Forecast

Archived

Jan 21st, 2016–Jan 22nd, 2016

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, human triggered possible.

Regions

Mt Hood.

Loose wet avalanches should be the main avalanche problem Friday with plenty of wet snow in the upper snowpack. Natural avalanches are unlikely but human triggered avalanches are possible on steeper slopes. Be especially wary near terrain traps, where even a small avalanche could have unintended consequences.

Detailed Forecast

Light precipitation Thursday night with a slow cooling trend should transition to light to moderate showers with snow levels falling to 4500 feet by Friday afternoon. Light amounts of new snow should bond well to the wet and refreezing surface on Friday. 

Loose wet avalanches should be the main avalanche problem Friday with plenty of wet snow in the upper snowpack. Natural avalanches are unlikely but human triggered avalanches are possible on steeper slopes. Be especially wary near terrain traps, where even a small avalanche could have unintended consequences.

New wind slab may begin to build on lee easterly slopes near and above treeline Friday but should be fairly shallow. 

 

Snowpack Discussion

A continuous period of active weather for about the past week has brought several feet of snow to NWAC stations at Mt Hood. Fluctuating snow levels over this period has occasionally mixed rain up into the near treeline elevation band earlier in this storm cycle.

Most recently, roughly 2 feet of new snow accumulated Tuesday and Tuesday night at Timberline and Meadows NWAC base stations with consistent westerly transport winds buffeting the near and above treeline that continued through Wednesday afternoon.  

Meadows pro-patrol reported an active day of avalanche control on Wednesday with all the new snow. Storm and wind slab releases, mostly initiated with explosives but also sensitive to ski cutting, ranged from 1 to 3 feet, with the larger slabs on lee aspects near and above treeline. Wind affects were seen well into the below treeline band, and also allowed hard slabs to form on lee slopes higher in the terrain. Debris from a natural avalanche was observed in White River Canyon at around 8000'.

Periods of light and high freezing levels were seen on Thursday along with moderate and consistent SW winds near and above treeline.  

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.