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Avalanche Forecast

Archived

Dec 16th, 2015–Dec 17th, 2015

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

Regions

Mt Hood.

Travel in avalanche terrain is not recommended Thursday, especially near and above treeline where larger and more dangerous avalanches are possible. 

Detailed Forecast

A strong Pacific frontal system on Thursday should bring heavy precipitation to the Mt. Hood area along with a strong warming trend.  

As snowfall and winds increase, avoid steeper slopes and watch for increasingly sensitive storm layers. A rising rain-line should also activate storm slabs throughout the day. At lower elevations that change to rain quickly, watch for small loose wet avalanches on steeper slopes and near terrain traps. 

New and recent snow will be deposited on lee NW through SE aspects near and above treeline. Most avalanches should stay within the new storm snow, but some may step down to older storm layers or crusts producing larger avalanches.    

Travel in avalanche terrain is not recommended Thursday due to dangerous avalanche conditions, especially near and above treeline. 

The elevated avalanche danger will continue Thursday night into Friday morning.  

Terrain anchors are still causing significant anchoring at the lowest elevations. Use caution near creeks which are still open in some areas.

Snowpack Discussion

An atmospheric river around Dec 9th pushed heavy rain up well above 7000 feet in the Mt. Hood area. Below these elevations water percolated down below the early December crust (date at which when the crust was buried). An active and cool weather pattern over the last week has produced about 2 to 4 plus feet of new snowfall that now sits over the 12/9 crust. The below treeline zone snowdepth is filling in nicely but still contains many barely hidden hazards like rocks, streams or snags. The skiing in non-wind affected areas with enough snow cover has been good! 

The Meadows pro patrol on Sunday reported sensitive explosive releases on most lee slopes up to 6600 feet. Numerous soft slabs ran their full paths, releasing in storm layers. The Meadows pro patrol on Monday still reported avalanches of increasing size with increasing elevation. At 6800 feet, avalanche control triggered a 3-5 foot hard wind slab on a northeast slope which released on the rain crust from last week. Ski cuts generally produced isolated 6-8 inch releases. The Meadows pro patrol on Tuesday reported that wind Monday night had greatly rearranged the snow into sastrugi and wind slab down to the below tree line zone but no new avalanches were triggered or reported.  W through NW winds above treeline may have further loaded lee slopes Tuesday night and early Wednesday.  

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.