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Avalanche Forecast

Archived

Dec 24th, 2015–Dec 25th, 2015

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

Regions

Olympics.

A consolidating and stabilizing trend should begin by Friday. But recent wind slab, storm slab, loose dry snow and tree wells will all still be key features to avoid on Thursday.

Detailed Forecast

An upper trough and cool air mass will sink to the south of the Northwest on Friday. Alpine winds should decrease and become northwest with light snow showers ending over the Olympics by Friday morning. Some sun should be seen at Hurricane by Friday afternoon.

This weather should not build new snow pack layers and a gradual consolidating and stabilizing trend should begin by Friday. Cool temperatures may somewhat slow the stabilizing but the avalanche danger should be less than the previous couple days.

Recent wind slab will be most likely to linger on north to east slopes in the above and near tree line. Wind and storm slab avalanches should remain within recent storm layers but could still move fast. Test for inverted strong over weak storm snow and give cornices a wide margin.

Beware of loose dry avalanches in steep non-wind affected terrain that could have unintended consequences such as knocking you off your feet and into a terrain trap.

Remember to discuss plans with your partners or steer clear of high consequence terrain until there is more information and we know more about what is going on out there.

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

Snowpack Discussion

We have had nearly a week of heavy snow and cool temperatures in the Olympics and Cascades. It looks like Hurricane Ridge has received about 4 feet of snowfall in the past week. The last rain event at Hurricane Ridge was December 17th.

NWAC pro observer Matt Schonwald and an NPS ranger toured around Hurricane Ridge last Friday. 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.

 

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.