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Avalanche Forecast

Archived

Jan 30th, 2016–Jan 31st, 2016

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

Regions

Olympics.

The greatest avalanche problem should be wind slab on lee slopes near or above treeline mainly NW-N-SE facing slopes below ridges. Watch for signs of firmer wind transported snow.

Detailed Forecast

Light winds and occasional light snow showers with continued cool temperatures should be seen on Sunday. A skiers delight! But continue to evaluate snow and terrain carefully on Sunday.

This weather should bring a gradually decreasing avalanche danger on Sunday. Storm layers that may exist above the new crust will slowly settle but could remain reactive to human triggers mainly in the above treeline Sunday. 

The greatest avalanche problem should be wind slab on lee slopes near or above treeline mainly NW-N-SE facing slopes below ridges. Watch for signs of firmer wind transported snow.

Watch for storm slab in areas that had rapidly accumulating snowfall.

Watch for newly formed cornices along ridges as well. These may be sensitive to human triggers.

Below treeline, the old wet snowpack should continue to drain and slowly refreeze.

Snowpack Discussion

Heavy rain fell in the Olympics Wednesday-Thursday. Over 2 inches of rain was recorded at the NWAC station at Hurricane Ridge by Thursday midday. This rain event should give the snowpack a new horizon going forward.

The "20th of June" path released as a wet slab during rain and warmth last Thursday. Photo taken January 29th by Matt Schonwald.

A strong occluded front with strong winds crossed the Northwest on Friday. The Hurricane rangers report about 14 inches of new for the 2 days ending Saturday morning.

NWAC pro-observer Matt Schonwald visited Hurricane on Friday and found rapidly building wind slab and extensive loading on lee slopes in all 3 elevations bands. New cornices were sensitive to trigger but still relatively small. The bonding of the new snow to the forming crust was strong but there was a thin layer of low density stellar crystals above the crust, forming the weak layer for newly forming wind slabs to fail.

In the below treeline zone, a strong crust with shallow new snow should cause less danger, but watch for shallow wind deposited snow on isolated features, such as cross loaded ribs or slopes convexities. 

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.