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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Saturday, February 25th 2017
Created: Feb 25th 4:27 am
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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The Bottom Line

The avalanche danger is MODERATE above 2,000' in the Alpine where triggering a 2-3' slab avalanche on slopes steeper than 35 degrees is still a possibility on all aspects. In addition, there are a handful of other avalanche concerns including shallow wind slabs, cornice falls, sluffs and glide avalanches. 

Below 2,000' there is a LOW danger where triggering an avalanche is unlikely due to a snowpack consisting of hard crusts.

In Summit Lake, Girdwood, and on the southern end of Turnagain near Johnson Pass triggering a deeper more dangerous avalanche near the ground is still possible, but will be hard to trigger.

Check out the Saturday Summit Summary HERE.


Primary Concern

Above 2000' where the rain crusts disappear the layer of surface hoar that was buried by the mid February storms is lingering as a concern in the advisory area. Relatively calm weather has been over the region for a few days now. This has allowed for folks to push further into the mountains with no reports of avalanche activity since last Saturday. However, this weekend it is important remember that poor snowpack structure still exists with this thin layer of buried surface hoar sitting 2-3' below the surface and the slab is large enough that the consequences could be high if you find the wrong spot. Triggering an avalanche breaking on this layer is becoming tougher by the day as the snowpack slowly stabilizes and adjusts but the possibility shouldn't be forgotten. 

The most likely place to find one of these larger slides is on steep slopes with thin areas and rock bands. Trigger points are often these thin areas, near rocks and zones that may have been scoured slightly by winds. Also, these slabs can break above you, and release after several tracks are on a slope. Be aware that snow pits and stability tests may not be representative of the actual slope you are trying to assess. A helpful way to think about this problem is to consider the consequences of a slope if it slides and identify and avoid terrain traps (gullies, cliffs, or trees below).

Deep Persistent Slab: Various layers of weak faceted snow sits at the bottom of the pack in certain areas. In the Summit Lake zone and some areas in Girdwood Valley and towards the southern end of Turnagain near Johnson Pass depth hoar has been found. Similar to the problem above, these layers will be very tough to trigger, but a possibility remains in places with this structure. 

Snow pit profile from Sunburst on Tuesday. Note the structure: buried surface hoar sandwiched below a stiff slab and stiff potential bed surface.

 

Snow pit on Thursday showed similar stucture across the road on Seattle Ridge.  In both locations tests showed that the layer was harder to trigger but still a possibility.

 


Secondary Concern

Wind slabs: Loose surface snow combined with W-NW ridgetop winds in the 10-20 mph range gusting into the 30s overnight may have formed shallow wind slabs on leeward features. The snow may feel "upside down" with slightly stiffer snow over softer snow. Look for areas of pillowed or drifted snow and identify steep features like convexities or gullies where the snow may be more loaded.  Blowing snow and shooting cracks will be obvious clues to look for today. 

Loose snow avalanches: The top 6” of surface snow is loose and sluffs may be easy to initiate and fast moving on steep terrain features protected from the winds. 

Cornices: Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche on the slope below. Give cornices extra space and avoid being under them. 

Glide avalanches: There is a new glide crack above the flats along Seattle Ridge, just looker's left of the up-track and Repeat Offender slide path. Avoid hanging out under this crack and any others you may see - these release without warning and are very destructive.

Sunshine: Today skies may be be partly sunny and solar warming may trigger loose snow avalanches in steep Southerly aspects. 

Wind effect just South of Pyramid Peak on Thursday.

 


Mountain Weather

Yesterday was mostly cloudy with a few light snow showers during the day favoring Girdwood. Temperatures were in the mid to high 20Fs with a few low elevation stations seeing above freezing for a few hours. Winds were light during the day and then picked up overnight from the W-NW 10-20 mph gusting into the 30s.

There was clearing overnight but clouds are forecasted to move back in today. Temperatures will be similar to yesterday and winds will be light and continue to be from the NW. There is a slight chance of snow overnight tonight. 

Sunday looks to be similar with an increasing chance of snow showers into Monday. Cold, clear weather is forecasted later next week. 

PRECIPITATION 24-hour data (6am - 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27  0 67 
Summit Lake (1400') 24 32
Alyeska Mid (1700') 24   1 .05 62

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24 WNW 10  32 
Seattle Ridge(2400')  26  NW 15  39 

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: May 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be 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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If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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