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Avalanche Forecast

Archived

Dec 31st, 2017–Jan 1st, 2018

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.
Below Treeline
Natural avalanches unlikely.

Regions

Olympics.

Keep an eye out for signs of wind transported snow such as fresh cornices, uneven snow surfaces, and wind drifts. Avoid areas of wind deposited snow, especially above treeline where more soft snow is available for transport.

Detailed Forecast

The New Year will kick off with another day of mild weather in the Olympics. Mostly sunny skies and warm temperatures will create yet another day for the snowpack to gain strength.

Watch for lingering wind slabs in exposed terrain, especially above treeline. Look for signs of wind transported snow such as uneven snow surfaces, fresh cornices, and snow drifts. Each of these observations are signs that the wind has redistributed snow in the area. Identify and avoid wind loaded terrain features.

Wind slabs can be deceptively difficult to manage in the terrain. Take a moment and read our recent blog post by NWAC Pro Observer Jeremy Allyn on wind slabs.

 

Snowpack Discussion

Happy New Year from your friends at NWAC!

Mild weather Sunday allowed the snowpack to continue to heal and gain strength following an active weather pattern this past week.

SW winds Friday night redistributed new snow forming shallow wind slabs on lee slopes at higher elevations. This resulted in a variety of snow surfaces including soft unconsolidated snow, wind scoured slopes, rain crust, and firm wind slabs.

Friday’s warm weather resulted in a rain crust at most elevations. Limited information has been received about the extent, supportability, and bonding of new snow to this crust.

The 12/16 mid-December crust can still be found 2-3feet down within the snowpack.

Observations

NWAC pro observer, Matt Schonwald visited Hurricane Ridge on Friday, 12/29 and stressed that this is a different snowpack than the Cascades! He visited W-NW-N-NE aspects and found the 12/16 crust and 1-2 mm facets down 2.5 feet. Several PST tests failures, self-arrested, but propagated through most of the column along the 12/16 layer. This indicates that a persistent slab layer could be triggered most likely on large convex slopes below the ridgelines.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.