Avalanche Forecast
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. Â
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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.Â
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.Â
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!Â
Avalanche Problems
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1