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Avalanche Forecast

Archived

Jan 31st, 2016–Feb 1st, 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 and above treeline mainly NW-N-SE facing slopes. Watch for signs of firmer wind transported snow.

Detailed Forecast

Light winds, mostly cloudy weather, a few light snow showers and cool temperatures should be seen in the Olympics on Monday.

This weather should bring a further gradually decreasing avalanche danger on Monday.

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

Watch for storm slab in areas that had rapidly accumulating snowfall. Storm layers that may exist above the new crust will slowly settle but could remain reactive to human triggers mainly near and above treeline.

Continue to evaluate snow and terrain carefully on Monday.

Avoid ridges where cornices may be present and slopes below cornices. Cornices can always be sensitive to human triggers.

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 reported about 14 inches of new snow 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 elevation 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 will cause less danger. 

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.