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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Thursday, December 29th 2016
Created: Dec 29th 4:19 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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
Alaska Alpine Adventures LLC
Special Announcement

The Girdwood to Bird bike path is now CLOSED for the winter season. Remember this crosses below multiple large avalanche paths. Violation of this closure can result in a fine from Chugach State Park. 

A strong winter storm is on track to affect Hatcher Pass. Check current Hatcher Observations HERE and remember to check the Hatcher Pass Avalanche Advisory that is published every Saturday HERE

Join the Friends of the CNFAIC TONIGHT at the Beartooth Theatre, 8 pm for the newest film in this backcountry snowmachine series, 509 Films: Volume 11. More info HERE

 


The Bottom Line

The avalanche danger is CONSIDERABLE in the Alpine and human triggered wind slabs are likely on leeward slopes. It will be also possible to trigger a slab 2-3' thick on older buried weak layers. 

At Treeline in the mid-elevation band (1000'-2500') the avalanche danger is MODERATE. It is possible to trigger a 2-3' slab on older buried weak layers and it may slide to the ground.

Overall the snowpack is getting less likely to trigger but the consequences remain high if an avalanche is initiated.

LOW avalanche danger exists below 1000’ where the snowpack has a firm crust and triggering an avalanche is unlikely. 

Check out the Summit Lake Summary HERE

 


Primary Concern

Yesterday a westerly flow moved over area in the early afternoon and winds increased into the 20s gusting into the 40s. This continued through the evening. The way this wind direction shows up in terrain can cause unusual loading patterns. The winds blew from the South on the Sunburst/Tincan side of the road loading N slopes. On Seattle Ridge the winds were from the W/NW and loaded more easterly slopes. These patterns were varied around Girdwood, Portage and Summit Lake as well. There was a few inches of light fluffy new snow that was easily moved as well as soft settling snow from the Xmas storm. Expect fresh wind slab in leeward areas. Look for cracking and pillowed snow. These may be quite tender and reactive. The winds also had the potential to stiffen the slab sitting over older weak layers, add load to the snowpack and make it possible to trigger a deeper avalanche.  

 Wind on Sunburst yesterday.

 

 

 


Secondary Concern

Many people have been out enjoying the recent snow with no incident and for the most part avoiding steep slopes. There have been no reported human triggered avalanches since Monday and the natural avalanche cycle associated with the storm also ended that day. As visibility has improved is easy to see the remnants of this cycle. Many areas have had large slides that we suspect ran on the December 24th surface hoar, the December 15th layer of surface hoar or buried facets deeper in the pack. In addition there was a number of mid-elevation band slides that also ran on buried weak layers, some even running on facets just above the ground. The slides at all elevations are mostly 2-4' thick. There are areas adjacent to those that slid that may still have the potential to go today. It is important to remember thinner areas are often the place that old weak layers are initiated. The snowpack is still complex and it may be harder to initiate but the slides could still be large and deadly. Observers yesterday still reported large whumpfs and shooting cracks. These are red flags and a good indication to stay away from avalanche terrain if encountered. As you choose terrain to ride or ski today think about how large and connected it might be. It may not be the 1st snowmachine rider or skier onto the slope that triggers it. Triggering a deep persistent slab is possible and winds from yesterday may have added stress/load.

Slide on North side of Magnum believed to have run Monday December 26th. Photo: Andy Moderow

The December 24th layer of buried surface hoar visible in the snowpack on Sunburst and still reactive in instability tests.

 


Additional Concern

Expect cornices to be sensitive and easy to break off. They also could trigger a slab avalanche below. Be extra cautious near ridgelines today where cornices can be challenging to navigate.  If you suspect a corniced ridge give these a wide berth and be aware of people below you. Due to the unsusal wind loading yesterday look for new cornices or unsual loading patterns. 

 

 

Sunburst Cornice 12.28.16


Mountain Weather

Yesterday was mostly cloudy with a few light snowflakes falling. Winds were WNW and increased in the afternoon gusting into the 40s.Temperatures were in the low 20Fs and teens. Temperatures dropped to single digits overnight.

Today will mostly cloudy with the snow starting in the late afternoon. Temperatures will rise again into the 20s. Overnight the temperatures at lower elevations may rise into the low 30s and a rain/snow mix is expected with the storm system as it moves into the area. 2-6" of snow is possible overnight. Winds will be light and Southerly.

Tomorrow snow showers will continue and temperatures will drop back into the low 20s. Winds will be variable as the system passes through. The pattern continues to be unsettled into next week as a series of fronts move off of the Pacific. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 19   0  39
Summit Lake (1400')  15  0  0 10 
Alyeska Mid (1700')  20  0  0  27

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') n/a  n/a   n/a  n/a
Seattle Ridge(2400')  14 NW   22 42 

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: Mar 15, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: OpenSkookum drainage closes to motorized use on April 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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