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Avalanche Forecast

Archived

Apr 5th, 2017–Apr 6th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Loose wet avalanches should be seen in all areas in the near and below treeline bands or on solar aspects during periods of extended sunshine. New storm and wind slab problems will be shallow and limited to the above treeline elevation band for the Olympics. 

Detailed Forecast

A stalled frontal boundary oriented north-south and to the west of the Cascades will finally lift to the northeast and out of the area Thursday morning. After a period of light to moderate rain and snow, light post-frontal showers will follow in the afternoon along with sunbreaks. 

Loose wet avalanches should be seen in all areas in the near and below treeline bands or on solar aspects during periods of extended sunshine. Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger.

New storm and wind slab problems will be shallow and limited to the above treeline elevation band for the Olympics. Treat recently wind loaded slopes with caution with fresh wind slab most likely on NW-SE aspects above treeline.

Recent cornices are very large and have likely been weakened during this most recent storm cycle. 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.

Snowpack Discussion

Weather and Snowpack 

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.

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 that caused some light amounts of snow at much cooler temperatures on Sunday. 

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. 

A stalled frontal boundary on Wednesday brought heavy rain and snow to the Mt. Baker area with much much lighter precipitation for the central-west and southwest Cascades and the Olympics. Snow levels were generally between 4500-5500 feet on Wednesday. 

Recent Observations

No recent observations from Hurricane.

Problems

Loose Wet

Loose Wet avalanches are the 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. 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.

Wind Slabs

Wind Slab avalanches are the 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.

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 drifts 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.