Avalanche Forecast
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.Â
A series of frontal systems produced snow over the week following Thanksgiving: NWAC stations at Mt. Hood received about 2 feet of snow.Â
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.
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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.
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, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1