Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Wednesday, January 9th 2013
Created: Jan 9th 5:56 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
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The Bottom Line

Sunny skies today after 2 solid weeks of stormy weather will make today the most likely day for somebody to die in an avalanche.  Another large avalanche was triggered late yesterday in Turnagain Pass on the snowmachine route up to Seattle Ridge.  The snowpack is still reactive to human triggers, and despite a decreasing possibility of causing an avalanche, if one is triggered it will be large, deep, and deadly.  A CONSIDERABLE hazard can be found above treeline, meaning human triggered avalanches are likely.  Conservative route choices are essential.  

Primary Concern

Last night we got reports of an avalanche on Repeat Offender, the site of the large fatal avalanche in 1999.  A group of snowmachiners had just started descending the standard trail from Seattle ridge when it released remotely 100 yards away.  Initial reports estimate the size as 600-1200 feet wide.  It undoubtedly took the entire depth of the snowpack, breaking on old October and November weak layers.  Reports say that Main Bowl also slid on the west side of the ridge.

The deep slab problem is difficult to understand because it won't show signs of instability until it avalanches in a big way.  You also won't see a lot of slopes avalanching on the same day, meaning that the mountains will look good and enticing.  The problem is that when you find a trigger point, the resulting slide will be much bigger than you want.  This is a low frequency, but very high consequence problem that is difficult to predict.

We have compiled ample evidence to show that the mountains are ripe for this to happen again.  Over 10 feet of new snow in the last 2 weeks has already brought down a number of large avalanches including at Tincan, Seattle ridge, Johnson Pass, Portage, and elsewhere.  This is the most dangerous persistent deep slab problem we've had in our region in a number of years.  The only way to avoid becoming a statistic is to alter our behavior and choose conservative, lower angle terrain.

Secondary Concern

Yesterday we found a small reactive wind slab in the top 6 inches of surface snow at treeline.  Wind deposit areas may have this layer of stiffer, less stable snow.  Compared to the deep slab issue, this is a relatively minor and manageable problem. 

Mountain Weather

A few inches of colder snow fell yesterday with light wind in the mountains.  Today is likely to be the first day since December 22nd without any snowfall.  Expect sunny skies and light wind in the mountains with slightly colder temperatures. 

The clear weather will give way to another weak storm tonight, with snow expected again tomorrow and a return to warm and moist flow by the weekend.

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: Nov 18, 2017 )

Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedOnly a few inches of snow sits at the motorized lot, not enough to open for snowmachining at this time. Updated Nov. 18, 2017
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.

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