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Avalanche Forecast

Archived

Mar 30th, 2017–Mar 31st, 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

Olympics.

Sunshine and warming temperatures will make loose wet avalanches increasingly likely Friday. By afternoon, small wet snow avalanches may entrain deeper wet snow layers and become large. Use caution in steep sun exposed terrain during the warmest part of the day, avoiding steep slopes above terrain hazards such as trees or cliffs. 

Detailed Forecast

High pressure is expected to rebuild over the area Thursday night through Friday. This will cause clearing overnight and allow for wet surface snow to begin refreezing and strengthening.

Partly to mostly sunny conditions Friday and warming temperatures should cause a gradual increase in danger from wet snow avalanches, especially on slopes receiving direct sun and during the warmest part of the day.

Recent shallow wind slabs should continue to settle and stabilize where formed on lee slopes, mainly above treeline and on NW-SE aspects.

The expected clearing and cooling overnight Thursday should cause a strengthening surface crust by Friday. However, if previously wet surface snow has not refrozen, be suspicious of loose wet avalanches that may begin small but entrain older snow and become dangerous and difficult to manage. Pay particular attention to steep solar facing slopes above terrain traps such as trees, cliffs or gullies where being caught and carried, even in a small slide, could prove consequential.

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. 

Snowpack Discussion

Weather and Snowpack 

The first week of March was very cool and snowy. This was followed by periods of heavy rain in the second week of March. This caused significant avalanche cycles in most areas March 9-10. Significant snowpack consolidation occurred over this period due to rainfall and warmer temperatures. 

Another strong low pressure system brought several inches of rain to the west slopes of the Olympics and Cascades on Friday, 3/17 through early Saturday morning 3/18. Rapid cooling later Saturday morning was followed by generally light snow showers with little in the way of new snow accumulation. The rain event 3/18-19 has formed a very strong crust layer, now buried by this past 10 days storm snow.

The dominant wind pattern for the last several frontal systems have been moderate sustained S-SE winds. This has transported available snow to build fresh wind slabs in the Hurricane Ridge area.

Daily early spring warming temperatures have allowed surface snow melt and consolidation, at nearly the same rate as accumulations. With about 2 feet of snowfall received in the past week, the total snowdepth has increased only about 8 inches as of Thursday evening, 3/30. 

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.