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Avalanche Forecast

Archived

Jan 16th, 2016–Jan 17th, 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 at Hurricane Ridge on Sunday, especially near and above treeline. Careful snowpack evaluation, cautious route finding and conservative decision-making will be essential.

Detailed Forecast

Another front will bring more moderate rain and snow to the Olympics Sunday, beginning in the early morning and turning to moderate showers in the early afternoon. 

This weather will build generally upside down snow layers of increasing density near the surface and snow should also change to rain below treeline. About 6 inches should be seen at Hurricane by late Sunday afternoon.

New wind slab will also be very likely mainly on lee north to east slopes near and above treeline.

New storm slab due to the warming trend is also very likely on varied aspects where winds are lighter and snow rapidly accumulates to deeper than a few inches.

Small loose wet avalanche will again be likely below treeline in areas that see initial snow turn to rain Sunday, mainly on steeper slopes below treeline. 

Snowpack Discussion

Deep storm snow that fell during mid-late December is well settled, homogeneous and has stabilized so the current avalanche danger focus will be on the upper snowpack. Fair weather over the New Year caused extensive surface hoar and near surface faceted snow. This was buried by about 6 inches of snowfall at Hurricane about January 3-6th.

The last observation for Hurricane is from NWAC pro-observer Matt Schonwald at week ago and he generally found a right side up, stable snowpack. Older wind slab was limited to 6-12 inch (15-30 cm) pockets near ridges and tests indicated little propagation. Matt observed new surface hoar primarily on the sheltered north-east slopes. But this surface hoar was likely destroyed by mild temperatures and rain last Monday or Tuesday. Strong winds and rain up to at least 5500-6000 feet Tuesday likely caused a loose wet avalanche cycle on steeper slopes near and below treeline.

The latest period of snowfall has been from about January 11-16th. The NPS ranger reported about 2 inches of new snowfall Saturday morning with a likely change to rain later in the day. 

Problems

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.

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.