Avalanche Forecast
Regions: Mt Hood.
Travelers in the Mt Hood zone should chose conservative terrain Tuesday as recent wind slabs and wind stiffened surface snow are maintaining the likelihood of human triggered slab avalanches in exposed terrain near and above treeline. Avoid steeper terrain features with previous or newly forming firmer wind transported snow. Recent storm slabs may be preserved in the cool temperatures.
Detailed Forecast
Brief high pressure should rebuild along the PNW coastal areas Tuesday. This should maintain partly to mostly cloudy skies, light to moderate winds near treeline and continued cool temperatures.Â
This weather should maintain wind slabs near and above treeline with little change in the avalanche danger trend, as cool temperatures will slow the stabilization process especially in higher terrain.
Watch for wind stiffened snow and wind slab deposits on a variety of aspects, including non-traditional aspects from recent northerly winds.
Mt Hood is the zone most affected by current and recent wind affected snow and where travel plans should be more conservative Tuesday
Early season hazards still exist at lower elevations and especially around creek beds that are not filled in.
Snowpack Discussion
A disturbance moved across the southern WA Cascades and Mt Hood area Christmas Eve into Christmas Day, depositing 6-10 inches of storm snow, with moderate to strong winds near and above treeline. This has built new sensitive wind slabs near and above treeline as of Christmas Day.
About 15-18 inches of light snow fell at Mt Hood in the 24 hours ending Saturday morning.Â
A freezing rain layer formed Monday above about 6000 feet.
Moderate to strong SW-NW crest level winds transported snow in exposed terrain Tuesday to Thursday forming wind slabs on a variety of aspects.
Observations
On Christmas Day, the Mt Hood Meadows Pro Patrol produced sensitive 6-12 inches storm and wind slab avalanches near treeline, released with both ski cuts and small explosives. There was extensive propagation reported with some of the triggered slides. No control was performed above treeline due to active wind transport.
Backcountry observations from Thursday confirm wind redistribution of snow, with bare ridges and wind slabs on lee slopes observed.
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: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
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: All elevations.
Likelihood: Possible
Expected Size: 1 - 1