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Avalanche Forecast

Archived

Dec 2nd, 2016–Dec 3rd, 2016

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

Regions

Olympics.

Watch for left over wind slab on Saturday which may get covered by less cohesive snow Friday night.

Detailed Forecast

West winds will slightly decrease but not let up on Saturday with mostly light snow showers much of the day and cooler temperatures. However alpine west winds and snow should begin to increase in the afternoon as the next system approaches.

Shallow wind slab from Friday may linger on Saturday mainly on northwest to southeast slopes in the near and above treeline. Watch for firmer wind transported or hollow sounding snow. Wind slab from Friday may get covered by less cohesive snow Friday night making it harder to detect the underlying wind slab layer.

Avoid ridges that have a cornice and slopes below cornices.

Be prepared to change your plans if the next storm begins to arrive and significant snow begins to accumulate sooner than expected on Saturday afternoon.

In most of the lower part of the below treeline band there is still insufficient snow for avalanches but watch for early season hazards such as terrain traps, rocks and creeks.

Snowpack Discussion

A bit of a break was seen Thursday with snow showers tapering with 1 an inch of new snow at Hurricane ending Friday morning.

NWAC pro observer Matt Schonwald visited Hurricane on Thursday and reported lots of wind effects but a generally well bonded snow pack and snow profiles in pits that lacked a slab structure. The snow was found to be unconsolidated at lower elevations making terrain traps and creek crossings a hazard.

A front is crossing the area on Friday causing moderate to strong south to west alpine winds in the Olympics and Washington Cascades, hopefully with several inches of new snow at Hurricane and a warming trend.

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.

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.