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Avalanche Forecast

Archived

Dec 7th, 2017–Dec 8th, 2017

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

Regions

Mt Hood.

Wind slab should be possible on more varied aspects at Mt Hood than in other areas. Be especially wary of small loose wet avalanches near terrain traps. 

Detailed Forecast

Expect some high clouds and slightly cooler temperatures on Friday with light winds at higher elevations.

The avalanche danger should slightly decrease Thursday to Friday.

Recently formed wind slab is most likely to linger on non-solar slopes. Newer wind slab might be most likely on west aspects due to the recent northeast winds. Older wind slab should be found on more usual northwest to northeast aspects. The photo above shows that southeast aspects can't be ruled out. So wind slab should be considered a possible problem on all aspects. Wind slab should be stubborn or difficult to trigger. Watch for areas of firmer, wind-transported snow.

Snow on steep solar slopes should have mostly slid or consolidated in sunny warm weather on Thursday. Any high clouds and slightly cooler temperatures should diminish the danger of loose wet avalanches on Friday. But continue to watch for loose wet snow on steep solar slopes especially near sun warmed terrain features.

Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.

Snowpack Discussion

A series of frontal systems from post-Thanksgiving through the first weekend in December produced significant snowfall in the Mt. Hood area. There are no snowpack concerns below the Thanksgiving crust and in general new snow received post-Thanksgiving has reportedly bonded well. 

A series of frontal systems produced snow over the week following Thanksgiving: NWAC stations at Mt. Hood received 20-23" of snow. 

The active weather pattern was replaced with a high pressure system which brought sun initially cold temperatures Sunday and Monday. Generally northeasterly winds in the 10's and 20's with gusts to 30 mph plus at NWAC Mt. Hood sites slowed the warming Tuesday and Wednesday. But temperatures in the 40's and 50's were seen by Thursday.

Observations

On Monday, Patrol at Hood Meadows saw evidence of a natural wind slab that released after dark Sunday.

 

Natural wind slab release sometime Sunday night, 12/3. ESE facing wind loaded slope about 6600 feet. Photo: Brian Murphy

By Thursday the Mt Hood Meadows pro-patrol had little to report with just some shedding off rocks and trees in the sun and no other activity and snow staying cold on non-solar slopes.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.