Avalanche Forecast
Regions: Olympics.
A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. This should cause an increase in the avalanche danger on Wednesday in the Olympics mainly above treeline where there is significant snow.
Detailed Forecast
A big dose of warm front moisture will arrive in the Olympics and Cascades on Wednesday. Rain or snow should be heaviest in the Olympics and central to south Cascades Wednesday morning and shift to the north Cascades Wednesday afternoon and evening. Snow levels will be a moving target but the sure thing is they will be going up pretty rapidly on Wednesday. The main avalanche danger increase should be above treeline on the higher peaks of the Olympics.
The warming trend and initial snow will help build new upside down new storm slab where there is at least a few hours of snowfall of an inch or more an hour. In the Olympics this should be likely above treeline on Wednesday morning.
The warming trend and initial snow will also help build new wind slab on lee slopes. In the Olympics this should also be likely above treeline on Wednesday morning.
A change to rain should generally be seen in the Olympics on Wednesday. This is likely to begin to cause a cycle of loose wet avalanches on many slopes above treeline Wednesday afternoon.
Most areas below treeline in the Olympics do not have enough snow to cause an avalanche danger.
Snowpack Discussion
The 16-18 inches of storm snow that fell March 14th-15th mostly melted at Hurricane Ridge. The total snow depth at the NWAC weather station settled or melted and lost 10 inches last week.
Just a few inches of new snow accumulated last weekend. Winds may have built some small cornices along ridges and built some small wind slabs on lee slopes.
A fairly vigorous low pressure system moved east over the Mt Hood area last night to this morning. The main snowfall was in the south Cascades with only about 3 inches at Hurricane.
Overall the snowpack remains meager at Hurricane. There is probably only enough recent snow for avalanches above treeline on the higher peaks of the Olympics.
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.
Likelihood: Likely
Expected Size: 1 - 1
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, North West.
Elevations: Alpine.
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.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1