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Avalanche Forecast

Archived

Dec 4th, 2015–Dec 5th, 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.

Lingering storm and wind slabs on lee N through SE aspects are possible on Saturday in the near and above treeline elevation bands.   

Detailed Forecast

The incoming frontal system on Saturday will largely steer clear of the Mt. Hood area until Saturday night.  With no new significant storm snow expected, avalanche problems should be contained to previously formed shallow storm and wind slab mainly on lee N through SE aspects near and above treeline. Part of the Moderate avalanche danger also represents a lack of observations from the above treeline zone at this point in the season.

Snowpack Discussion

Note: The snowpack discussion is for the entire west slopes of the Cascades, but the avalanche danger forecast varies by zone.  

 

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 a 5-7 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, with similarly sized and placed shallow slab releases during control work on Friday. 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

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.