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Avalanche Forecast

Archived

Jan 3rd, 2016–Jan 4th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

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

The recent clear weather is giving way to a return to light snow showers Sunday that should persist into Monday. Freezing levels should remain low.

A heightened avalanche danger should apply to wind-loaded slopes near and above treeline where east-southeast winds continue to build new wind slab on a variety of aspects. After several days of strong east winds, most of the available surface snow should have been stripped from the surface. But it may still remain possible to trigger a small slab avalanche on a loaded convex roll or some unsupported slope. Look for recently transported snow further downslope from ridgelines than you might expect.

Snowpack Discussion

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

By Thursday through Saturday, moderate to strong east-northeast winds had significantly scoured or transported available surface snow 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 wind slab was bonding to underlying snow and no natural or skier triggered avalanches were noted. Significant wind loading continued to occur on the upper mountain Friday and to lesser extent Saturday.

Other than well sun and wind protected slopes, mainly shaded slopes in the trees, most surface snow conditions have been transformed significantly by wind, sun and overall snowpack settlement over the past several days.  

Exhibit photo: surface snow sculpted by wind, active wind transport on ridge, center left: Photo: Laura Green

Problems

Wind Slabs

Wind Slab avalanches are the 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.