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Archived

Avalanche Forecast

Jan 1st, 2016–Jan 2nd, 2016
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Mt Hood.

Heightened avalanche danger should be specific to wind-loaded slopes at all elevation bands where recent east winds continue to build new wind slab.

Detailed Forecast

Another cool and sunny day is forecast Saturday, with moderate E-SE winds continuing to transport snow in the near and above treeline elevation bands.   

New wind slab will be the primary avalanche problem as easterly winds continue to build new wind slab, including but not limited to westerly aspects. Look for recently transported snow onto lee slopes further downslope from ridgelines than you might expect, including the below treeline elevation band due to the persistence of the easterlies.    

Snowpack Discussion

A cool and very snowy storm cycle brought 6-7 feet of snowfall to Mt Hood the week ending December 24th. Moderate additional accumulations in the past week have allowed the snowpack to slowly settle. A variety of surface conditions exist with firm windpack near and above treeline, scoured ridge-lines, sun crusts on solar aspects, and powder below treeline in sheltered terrain.  

The Mt Hood Meadow pro patrol reported an overall right side up upper snow pack, good stability, limited wind effects below 7500 feet and good skiing on Tuesday. However, by Thursday moderate to strong east-northeast winds had begun significant new snow transport onto lee westerly aspects mainly in the near and above treeline elevation bands. 

NWAC observer Laura Green was in the Newton Creek drainage Friday and found good skiing in non-wind affected terrain. Even on wind loaded slopes near treeline, the denser winds slab was cohesive to underlying snow and no natural or skier triggered avalanches were noted. Significant wind loading continued to occur on the upper mountain. 

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, South West, West, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1