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Avalanche Forecast

Archived

Apr 8th, 2017–Apr 9th, 2017

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

Dangerous avalanche conditions are expected at Hurricane on Sunday. Recent storm snow will become wet and unstable with direct sun and warming, late morning and afternoon. Small loose wet slides may entrain significant snow in steeper sun exposed terrain. 

Detailed Forecast

A break in storms is expected Sunday, allowing for sunshine and gradual warming. ?Light winds and sunshine should allow for recent storm snow to quickly become wet and weak, especially on steep slopes facing the sun during the late morning and afternoon. Loose wet avalanches should become increasingly likely in this terrain.

Watch for wet surface snow deeper than a few inches, pinwheels and initial natural releases that indicate an increasing loose wet avalanche danger. Be wary of steep slopes with terrain traps such as cliffs or if heavily treed, where even a small loose wet avalanche could have big consequences. Initial small loose wet avalanches may entrain significant wet snow and become dangerous quickly.

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.

Other avalanche problems not listed that may be encountered on Sunday include storm slabs in more sheltered areas above treeline that experienced rapidly accumulating snowfall for more than a few hours.

Remember that solar effects can rapidly increase the touchiness of various types of avalanches at this time of year, loose-wet, cornices, glide and wind slab to name a few.

Snowpack Discussion

Weather and Snowpack 

Several inches of rain fell in the Olympics 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 and early April.

Daily spring warming temperatures have allowed surface snow melt and consolidation at Hurricane at nearly the same rate as snow accumulations which should generally indicate strong near surface crust layers.

A frontal boundary Wednesday to Thursday morning brought rain and snow to the Olympics and Cascades. Snow levels were generally between 4500-6000 feet over the Olympics. In the 3 days ending Friday morning the NWAC station at Hurricane had about .75 inches of WE. This WE will have fallen as snow above the snow levels.

A deep low pressure system moved north just off the Washington coast on Friday and Friday night. This storm deposited about a foot of snow at Hurricane Ridge by early Saturday with very strong S winds Friday afternoon, averaging over 40 mph with gusts over 90 mph!

Cooling, diminishing showers and winds Saturday allowed for the storm snow to begin settling and stabilizing. 

Recent Observations

No recent observations from Hurricane Ridge.

Problems

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.

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.

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.