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

Regions

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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 should generally be shallow and primarily found near and above treeline. 

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. After a period of light to moderate rain and snow through late morning or mid-day, post-frontal showers, moderate at times in the northeast Cascades, will follow in the afternoon. More sunshine should mix in for the central-east and southeast Cascades in the afternoon. 

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 should generally be shallow and primarily found near and above treeline. 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

March was a wet and wild month for weather and avalanches in the Cascades. The last widespread avalanche cycle during this stretch occurred March 28th-29th.

A weak front crossed the Northwest on Saturday morning, causing very light precipitation along the east slopes of the Cascades. This was followed by an upper trough that brought 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 east slopes of the Cascades. Snow levels were generally between 4500-5500 feet on Wednesday. The NWAC station at Washington Pass showed up to 5 inches of new snow at the base station at Pass level followed by a warming trend and a slight increase in ridge-top winds out of the SSW. 

Recent Observations

No recent observations. 

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.