Avalanche Forecast
Regions: Mt Hood.
A mixed bag of ugly snow conditions and a high avalanche danger in the near and above treeline elevation bands is expected at Mt Hood on Friday. Backcountry travel in avalanche terrain especially in the near and above treeline bands is not recommended on Friday.
Detailed Forecast
The next weather system will move strongly to the Olympics and north Cascades Friday late morning and spread to the rest of the Cascades by Friday evening with fairly high snow levels.
A fairly broad brush will be applied to the avalanche forecast for Friday. Expect a mixed bag of ugly snow conditions and a high avalanche danger in the near and above treeline elevation bands at Mt Hood.
Wet snow and rain or warm temperatures should further build or activate wind and storm slab mainly in the above tree line band.
Recent snow will be available for activation by warm temperatures for potentially large loose wet avalanches at Mt Hood. Watch for surface wet snow deeper than a few inches and pinwheels or small natural loose wet avalanches that usually precede large loose wet avalanches.
But new snow and cooler temperatures should be seen by Saturday.
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Snowpack Discussion
Weather and Snowpack
A strong occluded front crossed the Northwest last Friday and Saturday. NWAC stations on Mt Hood received about 1.5 feet of new snow
Cool and benign weather settled over Mt. Hood the last few days with ample sunshine on Tuesday.
A cold front crossed the Northwest on Wednesday. A warm front is causing heavy snow at Mt Hood today. NWAC stations at Mt Hood for the 2 days ending Friday morning will have about 1.5-2 feet increasing damp or wet upside down snow!Â
Recent Observations
The Mt Hood Meadows pro-patrol today reported heavy snowfall and remotely and easily triggered widespread 1 foot wind slab mainly on north to southeast slopes along with storm slab in the near and above treeline. A combination of storm slab, loose wet avalanches and rollerballs was seen below treeline.
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, South East.
Elevations: Alpine.
Likelihood: Very Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine.
Likelihood: Very Likely
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.
Elevations: Treeline, Below Treeline.
Likelihood: Very Likely
Expected Size: 1 - 1