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Avalanche Forecast

Archived

Dec 23rd, 2015–Dec 24th, 2015

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

Regions

Olympics.

New or recent wind slab should be most likely on lee north to southeast facing slopes. Storm slab or loose dry avalanches in non-wind affected terrain mean you need to use extra caution around terrain traps. 

Detailed Forecast

A cool upper trough will continue to sink south over the Pacific Northwest on Thursday. West winds should begin to decrease Thursday initially in the Olympics and north Cascades. Snow showers may another few inches to Hurricane.

Dangerous avalanche conditions should persist Thursday especially in the near and above treeline zones where new or recent wind slab be likely. Wind or storm avalanches should remain within recent storm layers but could move fast. Watch for evidence of wind deposited snow or pillows. Test for inverted strong over weak storm snow and give cornices a wide margin.

Loose dry avalanches in non-wind affected terrain may be difficult to manage on steep slopes. Even a small loose dry avalanche could have unintended consequences such as knocking you off your feet and into a terrain trap.

Terrain anchors are still causing anchoring at the lowest elevations, but less and less with every storm passage!

Snowpack Discussion

A series of cool storms has deposited increasing storm snow at relatively low freezing levels since early December. The last rain event occurred to the Hurricane Ridge elevation on December 17th. By Thursday morning Hurricane Ridge will have received about 3 feet of snow in the past few days.

NWAC pro observer, Matt Schonwald and an NPS ranger traveled extensively Friday around Hurricane Ridge testing the recent storm snow. The snow pack was mostly unconsolidated low density surface snow with a gradually increasing density down to the well bonded crust, a very good profile as of late last week. No slab character was noted in the upper snowpack during testing. Only isolated wind slabs were noted with no releases. Extensive cornices were noted on north to northeast sides of ridges. Skiing was very good.

 

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.

Loose Dry

Loose Dry avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.