Avalanche Forecast
Regions: Mt Hood.
Dangerous avalanche conditions are expected Friday, near and above treeline. Best to limit objectives by avoiding steep or wind loaded slopes, watching for sensitive wind and storm slab layers. Recent and newly wind loaded slopes in the near and above treeline zone should be found on a variety of aspects Friday.
Detailed Forecast
A frontal system overnight should enhance and maintain strong winds and heavy precipitation rates at relatively high freezing levels, before changing to showers with cooling Friday.  Â
Avalanche problems Friday should be associated with new wind slab layers, especially near and above treeline and to a lesser extent possible storm slab layer. New and recent snow will be deposited on lee NW-SE aspects. Most avalanches should be confined to the new storm snow since Thursday, but a few may step down to older storm layers or crusts in isolated locations. Â
In areas near and below treeline, the warming and rain Thursday on Mt Hood, likely to near or above about 6500 feet, likely caused widespread natural avalanches on many steep slopes. This should limit the danger by Friday, especially as significant cooling begins to form new surface crust layers below the elevation that experienced rain or wet, heavy snow. This should limit any avalanches to mainly shallow new snow below treeline. Â
However, near and above treeline, increasing snowfall and winds are expected overnight Thursday and early Friday. This should cause sensitive storm layers. Therefore, best to avoid steeper slopes and those showing signs of recent wind loading. Â
Terrain anchors are still causing significant anchoring at the lowest elevations. Use caution near creeks which are still open in some areas.
Snowpack Discussion
An atmospheric river around Dec 9th pushed heavy rain up well above 7000 feet in the Mt. Hood area. Below these elevations liquid water percolated down below the early December crust (date when the crust was buried). An active and cool weather pattern over the last week has produced about 2 to 4 plus feet of new snowfall that now sits over the 12/9 crust. The below treeline zone snowdepth is filling in nicely, but still contains many barely hidden hazards like rocks, streams or snags.
A strong storm Thursday with rapid warming and heavy precipitation caused a rapidly changing and increased avalanche danger through the day Thursday. New wind and storm layers built rapidly and by midday was causing widespread avalanches.Â
Reports from pro patrol at Mt Hood Meadows Thursday indicated sensitive natural and triggered slab releases were occurring as the storm progressed through the day and temperatures warmed. Many sympathetic and very sensitive slabs were reported, involving the 8-12 inches of storm snow that had been received by mid-morning Thursday.  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, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2
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: Possible
Expected Size: 1 - 1