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Archived

Avalanche Forecast

Dec 11th, 2018–Dec 12th, 2018
Alpine
4: High
The avalanche danger rating in the alpine will be high
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
2: Moderate
The avalanche danger rating at treeline will be moderate
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Mt Hood.

Dangerous avalanche conditions will persist on Wednesday due to recent snow and wind.  Avoid exposure to avalanche terrain capable of producing large avalanches. Below treeline, due to early season conditions, small avalanches have a greater potential for injury due to exposed rocks and vegetation. 

Discussion

Discussion

Prior to Tuesday's warm storm, reports of persistent weak layers in the upper snowpack were not found to be reactive by Mt. Hood Meadows patrol during control work or in snowpack tests.  Keep this recent layering in mind and look for weak snow in the upper snowpack below the most recent storm snow.  If avalanches do occur on this layer, they may act in surprising ways including remote triggers and wide propagation.

Snowpack Discussion

Regional Synopsis coming soon. 

Avalanche Problems

Wind Slabs

Fresh winds slabs will likely be found at all elevation bands Wednesday. Strong winds will have created deeply drifted areas, firm hollow wind slabs, and areas stripped by the wind. When you encounter firm surface snow on steep slopes, know that avalanches may break above you. 

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: All elevations.

Likelihood: Very Likely

Expected Size: 1 - 1