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Olympics

Issued: 8:42 PM PST Friday, December 29, 2017
by Garth Ferber

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.

Message from Garth Ferber: today Friday December 29th I worked my last shift as an avalanche forecaster at the Northwest Avalanche Center. I started my career here in 1993 and am fortunate to have been able to work here with Mark Moore, Kenny Kramer, Dennis D'Amico and now Robert Hahn. I also have been fortunate to have been able to work with many great people in the NWAC partner groups over the years. You may not have heard the last of me, I may help part time with the NWAC weather stations in the future we will see. Cheers, Garth

A decreasing avalanche danger will be seen on Saturday. Watch for new signs of wind transported snow on lee slopes on Saturday. Avoid large terrain convexities on W-NW-N-NE slopes below ridgelines where the somewhat reactive 12/16 may be present until we know more about it.

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Avalanche Problems for Saturday

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 Saturday:

A change to moderate to strong WSW winds and cooling should be seen Friday night following the front. Hurricane should get about 2-4 inches of new snow with a cooling trend by Saturday morning.

Overall this will lead to a decreasing avalanche danger on Saturday. The expected modest new snow and the cooling trend should favor up right side up snow.

With the recent SSE winds and the change to WSW winds Friday night new wind slab is possible on about W-SE aspects. Avoid lee slopes with these aspects especially if you see signs of firmer wind transported snow.

The persistent slab at Hurricane seen by Matt is a low probability but high consequence avalanche problem. Avoid large terrain convexities on W-NW-N-NE slopes below ridgelines where the somewhat reactive 12/16 was found on Friday, until we know more about it.

Also 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:

We are at the tail end of a couple of days of very active changeable complex weather. On Thursday strong westerly flow aloft carried a very moist occluded front across the NW. On Friday a moderately deepening low pressure system is crossing the Cape Flattery area and a strong cold front will cross the Northwest Friday evening.

By Friday morning there was 3 inches of new snow that fell with an overall slight warming trend at Hurricane. Winds on Friday have been generally SSE 20's gust 40's on Friday with and it looks like the snow level rose enough for a change to rain at Hurricane.

Regular though ususally light snow also accumulated at Hurricane as very weak weather disturbances crossed the Northwest in about the past week. 

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 at 75-80 cm. 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 a large convex slopes below the ridgelines. Matt also noted wind slab developing with weaker storm layers down about 17 cm in recent snow and at 25 cm at recent/old snow interface.

No Corresponding Mountain Weather Forecast Available

USE AT YOUR OWN RISK

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.