Issued: 6:20 PM PST Saturday, December 30, 2017
by Kenny Kramer

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level.

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.

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Avalanche Problems for Sunday

Wind Slabi

Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.

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Persistent Slabi

Persistent slabs can be triggered by light loads and weeks after the last storm. You can trigger them remotely and they often propagate across and beyond terrain features that would otherwise confine wind and storm slabs. Give yourself a wide safety buffer to handle the uncertainty.

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Forecast for Sunday:

With mild weather prevailing, the snowpack will continue to adjust and 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.

Lots of uncertainty still exists around the potential for a Persistent Slab problem. Observations on the 12/16 crust continue to demonstrate that there is potential for avalanche on this layer. Signs of instability on the 12/16 crust will be difficult to gather, but any resulting avalanche could be very consequential.  Avoid large terrain convexities on W-NW-N-NE slopes below ridgelines where the somewhat reactive 12/16 layer was found on Friday.

Despite all the new snow, early season hazards still exist at some lower elevation locales and especially around creek beds that are not filled in.

Avalanche Summary:

Several inches of new snow fell in the Olympics Friday night into Saturday morning. SW winds overnight redistributed the new snow in exposed terrain forming new shallow wind slabs. This new snow and fresh wind slabs sit atop a rain crust formed during Friday’s warm temperatures.

A surface crust from mid-December can still be found within the snowpack. 2-3 feet of snow now rest on the 12/16 crust.


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, self-arrested, but propagated through most of the column along the 12/16 layer. This should indicate that a persistent slab layer could be triggered most likely on large convex slopes below the ridgelines. Matt also noted wind slab developing with weaker storm layers down about 6 inches in recent snow and at 10 inches at recent/old snow interface.

No Corresponding Mountain Weather Forecast Available


This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.