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Avalanche Forecast

Archived

Dec 5th, 2016–Dec 6th, 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.

A slow improvement should continue, but cold temperatures slow the settlement process and may preserve recent storm snow instabilities found on wind loaded aspects near and above treeline. In steep sheltered terrain, watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences.  

Detailed Forecast

Showers should end early Tuesday with a clearing trend and cold temperatures with light winds. This should allow for a further slowly improving trend in avalanche danger as any storm related weak layers further settle and stabilize. 

In particular, watch for lingering wind slab on lee aspects near and above treeline that can still be human triggered. 

In steep terrain where the new snow lacks a slab structure, watch for small loose dry avalanches near terrain traps like cliff bands where even small avalanches can have big consequences. 

Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks. 

Snowpack Discussion

Weather and Snowpack

A front crossed the Cascades Friday with around 2 inches of new snow reported at NWAC stations on Mt. Hood through early Saturday morning. A warming trend ahead of the front allowed a breakable freezing rain crust to develop up to at least 6800 feet.

A much stronger front crossed the area late Saturday night delivering a welcome 1-2 feet of snow at Mt. Hood stations through early afternoon Sunday. This system also ushered in the coldest air mass of the season. Further showers at cold temperatures deposited an additional 12 inches of snow by Monday evening. Storm snow amounts have now reached an impressive 2-3 feet or more since late Saturday.  

Avalanche problems should be confined to the most recent storm snow and  we are not tracking any weak layers in the lower or middle of the snowpack at this time. 

Recent Observations

Patrol at Mt Hood Meadows Sunday indicated a favorable snowpack profile with very limited slab like character noted, except for isolated features were wind deposited snow produced some very soft slab releases of little consequence.  

Pro-observer Laura Green was touring in Iron Creek Saturday and found a generally stable snowpack with obvious signs of recent wind transport with scoured windward aspects as she traveled near treeline. The Meadows pro-patrol had no significant avalanche control results Saturday. 

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.