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Avalanche Forecast

Archived

Jan 12th, 2016–Jan 13th, 2016

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

The avalanche danger should remain elevated in the morning with a slow decreasing trend through the afternoon as storm instabilities begin to stabilize. Cautious route-finding and terrain selection will be essential on Wednesday to stay safe and avoid storm related avalanche problems. 

Detailed Forecast

Moderate to heavy precipitation Tuesday night should moderate on Wednesday. A warming trend should occur Tuesday evening leading to a natural avalanche cycle involving the new storm snow. A slow cooling trend should begin late Tuesday night and continue through Wednesday with transport winds shifting from S-SW to NW by Wednesday afternoon. 

The avalanche danger should be elevated in the morning with a slow decreasing trend through the afternoon as storm instabilities begin to stabilize. Cautious route-finding and terrain selection will be essential on Wednesday to avoid storm related avalanche problems. 

Stay off steeper slopes and allow storm instabilities time to settle. Look for wind slab on a variety of aspects near and above treeline due to shifting winds. Watch for signs of firmer wind transported snow that can indicate wind slab layers near and below ridges.

Shallow loose wet avalanches are possible Wednesday below treeline on steeper slopes primarily in the morning.

Snowpack Discussion

About a week of fair weather was centered around the New Year. This allowed the heavy snow that fell during the strong storm cycle that ended about Christmas to settle and stabilize. Moderate to strong east-northeast winds in early January had significantly scoured most of the available surface snow in the near and above treeline elevation bands.

No avalanches have been reported over the past several days on Mt Hood. 

As of 4 pm Tuesday, a little less than an inch of water received during the day had translated into 5-6 inches of heavy snow at the base Timberline and Mt. Hood Meadows NWAC stations. Warm air has been slow to work it's way around the mountain, with temperatures just beginning to climb above freezing at Timberline Wednesday afternoon while still below freezing at Meadows. Winds have been strongest above treeline from the south or southwest.  

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.

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.