Avalanche Forecast
Regions: Mt Hood.
While less new avalanche danger is expected at Mt Hood than in the Washington Cascades you will need to use extra caution on specific terrain features and evaluate snow and terrain carefully on Wednesday. The forecast at Mt Hood is quite uncertain and be prepared to scale back your plans if snow and rain is heavier than expected on Wednesday.
Detailed Forecast
Heads up because winter isn't done yet and the quiet weather and snowpack seen the past couple days is going to see significant snow and rain depending on location on Wednesday!
A front will stall over the Northwest on Wednesday with a series of waves moving south to north along the front. Precipitation should fall as snow in the above treeline and perhaps down into the near treeline zones. Rain and snow is expected to be less at Mt Hood than in the Washington Cascades.
New shallow storm slab may build in the above and perhaps down into the near treeline at Mt Hood where there is rapidly accumulating new snowfall. New storm slab should be very touchy especially if there is a daytime warning trend.
Loose wet avalanches should be possible in the near and below treeline at Mt Hood. Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger.
Recent cornices are large and will get new loads on Wednesday. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes below large cornices. See a blog post regarding cornices here.
New wind slabs won't be added to the list of avalanche problems at Mt Hood on Wednesday but may also build in the above and perhaps down into the near treeline. New wind slab should also be very touchy especially if there is a daytime warning trend.
While less new avalanche danger is expected at Mt Hood than in the Washington Cascades on Wednesday the forecast here is quite uncertain. Be prepared to scale back your plans if snow and rain is heavier than expected.
Snowpack Discussion
Weather and Snowpack
March was wet and wild for weather and avalanches in the Cascades.Â
The last major system in March was seen Tuesday and Wednesday when a strong low pressure system brought rising snow levels and locally heavy precipitation along the west slopes of the Cascades including Mt. Hood. After receiving a few inches of snow Tuesday night, Mt. Hood saw periods of moderate to heavy rain to above 7000 feet on Wednesday.
Cooling and showery weather Thursday allowed wet snow to begin refreezing with 2-5 inches of new snow at NWAC stations at Mt Hood. The winds diminished Thursday and combined with daytime warming, this allowed for wind slab and storm slab to begin stabilizing.
A weak front crossed the Northwest on Saturday morning, causing light rain mainly along the Cascade west slopes. This was followed by an upper trough on that caused some light amounts of snow along the Cascade west slopes at much cooler temperatures on Sunday.Â
Fair but cool weather has been seen in the Olympics and Cascades Monday and Tuesday. Reports generally indicate strong surface or near surface crust layers and shallow recent snow.Â
Recent Observations
The storm limited observations on Wednesday, but rain quickly penetrated the upper snowpack in the Mt. Hood Meadows base area by late morning.Â
NWAC pro-observer Laura Green was in the White River area in the 4500-6000 ft range on Friday and reported 4-13 cm of recent snow on the P crust from mid week. Pit tests gave hard results that did not indicate propagation on a layer at 30 cm. She noted natural wind slab releases in the above treeline and loose wet avalanches below from Thursday.
The Meadows pro-patrol on Saturday and Sunday reported triggered loose wet avalanches becoming possible on solar slopes. Otherwise the recent crust is the predominate snow surface there with small shallow areas of wind transported snow been soaked by rain and frozen in place.
Avalanche Problems
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, 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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Cornices
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridgeline areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
A corniced ridgeline. A large cornice has formed at the top of the ridge. A smaller cornice has formed to the left of the trees from crossloading.
Cornices are easy to identify and are confined to lee and cross-loaded ridges, sub-ridges, and sharp convexities. They are easiest to trigger during periods of rapid growth (new snow and wind), rapid warming, and during rain-on-snow events. Cornices often catch people by surprise when they break farther back onto flatter areas than expected.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood: Possible
Expected Size: 1 - 2