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Avalanche Forecast

Archived

Dec 15th, 2015–Dec 16th, 2015

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

Regions

Mt Hood.

Previous layers will gradually stabilize on Tuesday but wind slab could still be triggered on previous lee slopes. Pay extra attention if you see winds transporting recent snow to new lee slopes.

Detailed Forecast

A weak cold front will cross the Northwest on Tuesday. This should bring northwest winds and cool temperatures but light snow should not reach Mt Hood until Tuesday night.

This weather should bring further gradual stabilizing of layers from late last week and the weekend. Previous wind slab layers from strong winds Saturday could still be triggered on previous lee slopes. Dangerous avalanche conditions are still expected above tree line making cautious route finding and conservative decision-making essential.

 Pay extra attention if you see winds transporting recent snow to new lee slopes.

Snowpack Discussion

An atmospheric river and warm very wet weather was seen last week. About 5-7 inches of rain was seen at Mt Hood. This caused an avalanche cycle, consolidation and stabilizing of the older part of the snowpack.

A stormy pattern with cooling was seen late last week and over the weekend with about 4-5 feet of snowfall at Mt Hood.

The Mt Hood ski area on Sunday reported sensitive explosive releases on most lee slopes up to 6600 feet as travel above that was avoided. Numerous soft slabs ran 100% of the paths and traveled far distances releasing in storm layers. These avalanches were on previously heavily skied paths indicating backcountry areas would likely have significantly deeper slab potential. The Mt Hood Meadows ski area 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 release on the rain crust from last week. Ski cuts generally gave just isolated 6-8 inch releases. A cool day with little if any new snowfall on Monday will have brought some stabilizing. Terrain anchors have been somewhat buried by recent snowfall but will still add significant anchoring below about 5000 feet. 

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.