Avalanche Forecast
Regions: Cascades - South East.
Loose-wet snow avalanches should remain possible in steep terrain. Use caution in steep terrain, especially if the surface snow is wet more than a few inches, avoiding steep slopes above terrain hazards such as trees or cliffs. Avoid travel on or below cornices.
Detailed Forecast
A warm, sunny day Friday allowed for further shallow melt and consolidation. Increasing clouds Friday night with light precipitation should maintain mild temperatures and allow for limited surface crust formation.
This weather should maintain shallow, moist to wet surface snow conditions Saturday.
Only light amounts of additional precipitation with a gradual cooling trend are expected Saturday. This should not appreciably change the overall avalanche danger through the day Saturday.
Expect shallow wet snow conditions over one or more strong near surface crust layers.
Recent shallow wind slabs should have mostly stabilized where formed on lee slopes, mainly above treeline and on NW-SE aspects.
Recent cornices are very large. Natural cornice releases and resulting slab avalanches are dangerous and unpredictable. Give cornices a wide berth if traveling along ridge-lines and avoid slopes directly below large cornices. See a blog post regarding cornices here.Â
Snowpack Discussion
Special Note: For more information on the massive natural cornice triggered avalanche on the north side of Ruby Mountain on Sunday 3/19 and general thoughts about low-likelihood/high consequence avalanches, please see NWAC's blog post issued Sunday, March 26.Â
Weather and Snowpack
Let's just say it's been a wet and wild few weeks regarding weather and avalanches in the Cascades.Â
This past week has also been active weather-wise, but water amounts/snowfall totals have been slightly lower relative to the extreme wetness of the past few weeks. NWAC and NRCS stations east of the Cascade crest had about 6-12 inches of snow in the 5 days ending Monday morning.Â
Another 5-10 inches fell near the Cascade crest along with a warming trend and increasing W-SW alpine winds Tuesday night and into Wednesday. Lesser amounts were seen further east of the crest and at lower elevations.Â
Cooling and showery weather Thursday allowed wet snow to begin refreezing with an additional 1-3 inches accumulating in most areas. The winds diminished by Thursday and combined with daytime warming, this has allowed for recent wind slabs to begin stabilizing.
Very mild temperatures and increased solar radiation Friday allowed for wet surface snow conditions in most terrain, even northerly facing slopes.
Recent Observations
North
The NCMG were in the Cutthroat area on Monday and found 15-20 cm of recent snow on a firm base. Loose wet avalanches and cornices were the main concerns.Â
On Tuesday, NCMG found stubborn and shallow storm slab in hand tests and on short slope tests. Very large cornices were still looming along ridge-lines. A public observation from the Washington Pass area on Tuesday reported shallow but sensitive wind slab on steep east aspects in wind affected terrain. Â
Central
No recent observations.Â
South
No recent observations.Â
Avalanche Problems
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, Treeline.
Likelihood: Unlikely
Expected Size: 1 - 2