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Avalanche Forecast

Archived

Apr 14th, 2017–Apr 15th, 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 unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Afternoon sunshine or sunbreaks should increase the loose wet potential on steeper solar aspects Saturday. Initially shallow loose wet avalanches could entrain deeper layers and become large in specific locations. Watch for lingering wind slab on lee slopes in steeper terrain primarily above treeline. Give cornices a wide safety margin.

Detailed Forecast

The cool upper level trough that's been plaguing the Pacific Northwest for several days should finally begin to loosen it's grip on the area Saturday. Partial clearing with afternoon sunbreaks are expected for the Olympics Saturday afternoon. Snow levels will remain low and winds should be light. 

After a cool night Friday, snow levels will remain on the cool side Saturday. However, afternoon sunshine or sunbreaks should increase the loose wet potential on steeper solar aspects Saturday. Initially shallow loose wet avalanches could entrain deeper layers and become large in specific locations. This time of year even brief sunbreaks combined with subtle daytime warming can quickly activate loose wet avalanches. Be especially wary of the loose wet avalanche potential near terrain traps. 

Older wind slab may still be sensitive and linger on lee slopes in steeper terrain, primarily on NW-SE slopes and above treeline on Saturday.  

Recent cornices are very large and resulting slab avalanches are dangerous and unpredictable. There have been numerous recent cornice failures with some being very large in the Washington Cascades. Five people were tragically killed by a cornice release in British Columbia on Saturday. 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 

Heavy rain received in mid March has left behind a well consolidated snowpack with one or more strong melt freeze crusts in the upper portion of the snowpack. 

A series of strong spring storms occurred during the first week of April.

Mostly sunny weather Tuesday helped storm snow begin to settle, however, winds remained strong enough above treeline Tuesday to continue to transport surface snow.

A weather system passing through the area Wednesday night produced about a third of an inch of water at Hurricane Ridge through Thursday morning. This translated to a few inches of new snow at Hurricane that quickly settled with daytime warming. Showers increased during the afternoon on Thursday and Friday with light additional snow accumulations likely mixing with graupel during more intense showers.

Recent Observations

No recent observations from Hurricane Ridge.

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.