Avalanche Forecast
Regions: Olympics.
Difficult and dangerous travel and avalanche conditions will develop in the back country on Wednesday where careful snow pack evaluation and cautious terrain choices will be essential.
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. This should cause periods of moderate to heavy rain or snow on the Washington volcanoes especially Mt Baker with light to moderate rain or snow in most other areas. Precipitation should fall as snow in the above treeline and perhaps down into the near treeline zones.
New storm slab should build in the above and perhaps down into the near treeline in most areas and will be deepest where there is the most new, rapidly accumulating new snowfall. New storm slab should be very touchy especially if there is a daytime warning trend.
Loose wet avalanches should be seen in all areas in the near and below treeline. 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 very 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 lengthy list of avalanche problems on Wednesday but should also build in the above and perhaps down into the near treeline in most areas. New wind slab should also be very touchy especially if there is a daytime warning trend.
Snowpack Discussion
Weather and SnowpackÂ
Several inches of rain fell in the Olympics and Cascades on Friday, 3/17 to Saturday 3/18. Rapid cooling following the event formed a very strong crust layer, now buried by snowfall in late March.
The dominant wind pattern for the last several frontal systems at Hurricane have been moderate sustained S-SE winds. This transported snow to build fresh wind slabs in the Hurricane Ridge area.
Daily early spring warming temperatures in late March have allowed surface snow melt and consolidation at Hurricane at nearly the same rate as snow accumulations which should generally indicate strong surface layers.
A weak front crossed the Northwest on Saturday morning, causing light rain at Hurricane. This was followed by an upper trough on that caused some light amounts of snow 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
No recent observations from Hurricane.
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: 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: Likely
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, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 2