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Avalanche Forecast

Archived

Feb 27th, 2016–Feb 28th, 2016

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

Regions

Olympics.

Dangerous avalanche conditions are expected Sunday especially in the near and above tree line. Careful snow evaluation and conservative decision-making should be essential on Sunday.

Detailed Forecast

A stronger cold front will cross the Northwest on Sunday. Expect increasing strong alpine winds and significantly increasing moderate to heavy rain or snow on Sunday. New snow amounts of about 5-10 inches should be seen in the near and above tree line by the end of the daylight hours.

This weather should transport snow and build new wind slab on lee slopes through the day. This should be mainly on N to E slopes in the above and near tree line bands. Watch for firmer wind transported snow and surface snow cracking from the tips of your skis.

New storm slab should also build through the day in areas that rapidly accumulate snow. This avalanche problem may work its way down into the upper treeline by the end of the day. Rapid snow accumulation is generally more than an inch or 2 an hour for several or more hours.

Dangerous avalanche conditions are expected by Sunday afternoon especially in the near and above tree line. Careful snow evaluation and conservative decision-making should be essential on Sunday.

The problem of loose wet avalanches will be left off the problem list on Sunday but watch for signs of significant wet snow at the lowest elevations.

Snowpack Discussion

Weather and Snowpack

The last snowfall occurred late last week when about a foot of snow fell ending February 20th. Some cornices and wind slabs formed during this period but recent warm weather and sunshine have likely settled and stabilized wind slabs.

Springlike weather under high pressure Wednesday and Thursday caused abundant sunshine with temperatures climbing into the upper 40's Thursday afternoon. This weather has allowed for melt-freeze crust formation overnight and varying amounts of wet surface snow depending on slope aspect.

A weak front brought mostly light rain to Hurricane Friday night to Saturday morning.

Recent Observations

NWAC pro-observer Matt Schonwald was at Hurricane Ridge Friday and found mostly consolidated stable snow. N to E slopes had areas of 25-30 cm of wind transported 4F snow well bonded to 1F MF grains in the upper snow pack. South slopes were melted out in some places with shallower dense stable snow in others.

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.