Avalanche Forecast
Regions: Mt Hood.
Watch for developing storm slabs, wind slabs and possible buried surface hoar, especially in areas receiving the heaviest snowfall with the strongest winds, such as at higher elevations. Choose very conservative terrain.
Detailed Forecast
Increasing storm conditions Saturday. Light rain and snow should increase Saturday morning through the day, becoming moderate to heavy with increasing westerly crest level winds. This should build unstable storm and wind slab layers through the day, with wind slabs spreading to NE-SE facing exposed terrain, especially below ridges by afternoon.Â
Expect dangerous avalanche conditions near and above treeline, especially by late Saturday afternoon. Careful snowpack evaluations, cautious routefinding and conservative decision-making will be essential Saturday.Â
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Snowpack Discussion
A warm plume of moisture moved over the Pacific Northwest last weekend. Exceptionally strong winds and heavy precipitation were recorded at Mt Hood; 9-12 inches of water fell at NWAC stations over 72 hrs ending 4 am Monday, 12/22 along with frequent gusts exceeding 100 mph in the alpine, wow! A natural avalanche cycle occurred on the upper mountain during this storm.  Â
The frontal system that impacted the area Tuesday evening through Wednesday started warm and ended cold for a right side up layering. Moderate to strong winds turned northwesterly with the cool-down... loading easterly aspects during the day. Winds were SW at the onset of this storm... and above treeline slopes were cross loaded.Â
New NWAC pro-observer C.J. Svela reported substantial wind transport Wednesday in White River Canyon in the near and above tree-line elevation bands. This translated to cracking on wind loaded slopes and sensitive cornices in the canyon.Â
News arrived from the Mt. Hood Meadow pro-patrol Thursday of a post control release. NW winds and additional snowfall continued to load non-traditional southerly lee slopes. A wind slab avalanche was skier triggered in bounds where 40-60 cm of stiffer snow overlaid a weaker layer at 6600 ft on a southerly aspect. Ski cuts produced few results, but the fracture was able to propagate along this interface in extended column tests. Â
Friday was a mostly cool and sunny day, which may have helped to settle recent layers.Â
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Avalanche Problems
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: All elevations.
Likelihood: Likely
Expected Size: 1 - 1
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 East, East, South East, South, South West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1