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Avalanche Forecast

Archived

Dec 6th, 2015–Dec 7th, 2015

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

Regions

Mt Hood.

New small storm and wind slab above treeline should be the focus on Sunday at Mt Hood.  

Detailed Forecast

The strong front that is bringing heavy snow and a warming trend to the Olympics and Washington Cascades on Saturday night and Sunday will bring much less new snow to Mt Hood. At Mt Hood only a few inches of new snow is expected. Winds may build some new small wind slab on lee north to east slopes. New small shallow storm slab is possible in calmer areas.

But  stronger system should begin to move into the Olympics and Cascades Sunday night. But be prepared to curtail your plans later Sunday if conditions deteriorate sooner than expected.

Early season hazards exist for much of the below treeline band throughout the Northwest, so ski and ride with caution.

Snowpack Discussion

We had a wild and wet month of November, with 18- 22 inches of water at Mt. Hood NWAC stations that unfortunately only amounted to a snowpack of 1-2 feet around 6000 feet. Strong high pressure led to steep temperature inversions over Thanksgiving weekend. The weather pattern has become more active for the first few days of December with about 10 inches of new snow at NWAC stations since the beginning of the month paired with moderate temperatures.

Avalanche and snowpack observations:  Mt. Hood Meadows professional patrol observed small natural slab avalanches on lee NE-E aspects near treeline Thursday to Saturday. The snowpack is rather thin, even up to 7000'.  No persistent weak layers have been observed or are expected in the Mt. Hood forecast area. The below treeline elevation band generally does not have enough snow to produce avalanches.

We still have many gaps in our observation network as it's early season, so make your own observations and use them in co-junction to our regional avalanche forecast. Thanks for reading the first NWAC avalanche forecast for 2015-16 season, stay safe and have fun! 

Problems

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.

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.