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Avalanche Forecast

Archived

Dec 8th, 2017–Dec 9th, 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.

A large natural wind slab avalanche was seen at Mt Hood Meadows early in the week. Continue to watch for firmer wind transported snow mainly on non solar slopes. Be especially wary of small loose wet avalanches on solar slopes near terrain traps. 

Detailed Forecast

Little change should be seen on Saturday with mostly sunny weather, warm temperatures at higher elevations, light alpine winds, with inversions and cool temperatures in the Cascade passes.

Due to mild temperatures at Mt Hood the snowpack should continue to gradually consolidate and strengthen, and the avalanche danger should continue to gradually decrease Friday to Saturday.

Recently formed wind slab is most likely to linger on non-solar slopes.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 late in the week. 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 about 2 feet of snow. 

An upper ridge this week has brought sunshine this week. The most recent active wind loading was by cold NE winds in the 10's and 20's with gusts to 30 mph plus at NWAC Mt. Hood sites on Tuesday and Wednesday. But winds decreased and  temperatures climbed into the 40's and 50's by Thursday and Friday.

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 and Friday 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 consolidating 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.