Avalanche Forecast
Regions: Mt Hood.
Use extra caution as you transition into wind-affected terrain as wind slabs may still be reactive to human trigger.
***A strong storm cycle is expected Thursday through Friday. The avalanche danger will likely reach warning criteria. Pay close attention to forecasts and be prepared to alter plans as we move towards the weekend.***
Detailed Forecast
The combination of increasing temperatures on Wednesday with cloudy skies, moderate westerly winds, and little snow available for transport should continue to allow wind slabs to stabilize.Â
Wind slabs were becoming significantly less reactive on 12/26 and that trend is expected to continue on Wednesday in the near and above treeline terrain.
Watch for wind stiffened snow and wind slab deposits on a variety of aspects, including non-traditional aspects from recent northerly winds.
There are a number of firmer layers in the snowpack, which may provide bed-surfaces for avalanches when the snowpack is loaded during anticipated storm and wind events Thursday and Friday.
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 with a freezing rain layer 1 cm thick forming at Mt. Hood Meadows toward the end of a storm which featured a warming trend and moderate to strong winds near and above treeline. This 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
Mt. Hood Meadows Pro Patrol reported two small and one large, explosive triggered avalanches on N and NE-facing terrain.
On 12/26 Mt. Hood Meadows Patrol reports that the new snow is wind-blown, chalky, and slabs are more stubborn. A 1 cm freezing rain crust exists near the surface.
On Christmas Day, the Mt Hood Meadows Pro Patrol produced sensitive small to large, 6-12 inches storm and wind slab avalanches near treeline, released with both ski cuts and small explosives on N and NE-facing terrain.. 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: Possible
Expected Size: 1 - 1