Avalanche Forecast
Regions: Mt Hood.
A decreasing avalanche danger is expected Saturday as wind slabs stabilize at higher elevations, while wet snow drains and continues to refreeze at lower elevations.
Detailed Forecast
Cloudy conditions with mostly light snow showers are expected through the day Saturday. Winds should remain light to moderate Saturday with only light snowfall accumulations.
This weather is not expected to increase the avalanche danger. Wind slabs formed late Thursday should continue to settle and stabilize at upper elevations. At lower elevations, wet or saturated snow should continue to drain and refreeze. This should allow for a gradual decreasing danger Saturday.Â
Continue to watch for recent wind slabs that formed Thursday night, mainly easterly facing terrain near ridges above treeline.
Snowpack Discussion
Weather and Snowpack
Yet another atmospheric river arrived Wednesday and Thursday brought heavy rain to all forecast elevations in the Mt Hood area. The storm total rain amounts ranged from over 2 to nearly 3 inches of water by Thursday morning.
A slow cooling trend through late Thursday with light to moderate snow showers deposited 5-8 inches of new snow late Thursday and Thursday night at mid and upper elevations above the hardening rain crust. A period of strong westerly winds accompanied these snow showers late Thursday, building new wind slab on lee slopes near and above treeline.
At lower elevations, below treeline, significant wet snow remains in the upper snowpack. The wet snowpack continues to drain and is beginning to slowly refreeze as of late Friday.Â
Recent Observations
NWAC observer Laura Green reporting from Mt Hood Meadows indicated the new 5-6 inches of snow received late Thursday was being rapidly transported, building fresh wind slabs on a variety of lee slopes from NE-SE facing below ridges. The bonding to the underlying wet snow appeared to be good initially.
Control results at Mt Hood Meadows early Friday produced 1 foot wind slab releases on lee terrain above treeline from artillery explosives. These slides would be the most recent wind slabs formed late Thursday. Elsewhere, controlled wind slab releases ranged from 6 inches to 1 foot, described as stubborn, and isolated. Below treeline, significant wet snow remained in the upper snowpack as of Friday. Â
Backcountry reports from Laura Green Friday indicated a whole mix of surface conditions. Firm rain crust near and above treeline with varying amounts of recent snow above, depending upon wind exposure. Isolated wind slabs had formed on the leeward terrain below ridges, with one natural wind slab noted in White River Canyon at about 7000 feet on ESE facing wind loaded slope. Elsewhere, firm conditions on an exposed hard rain crust.Â
Â
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, South.
Elevations: Alpine.
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.
Elevations: Below Treeline.
Likelihood: Unlikely
Expected Size: 1 - 1