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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Wednesday, February 22nd 2017
Created: Feb 22nd 4:24 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.
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.
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Special Announcement

Southern Kenai mountains; including the Seward zone (Lost Lake/Carter/Snug Harbor/etc):  Heavy precipitation, strong winds and warm temperatures last week have added several feet of new snow to these areas. Cautious route-finding is recommended as avalanche conditions may still be dangerous.

Other regions throughout Southcentral, AK continue to have heightened avalanche conditions including Chugach State Park and Hatcher Pass

 


The Bottom Line

There is a MODERATE avalanche danger on all aspects above 1,500' where triggering a slab avalanche 2-3' thick is possible on slopes steeper than 35 degrees and could have high consequences. In addition there are a handful of other avalanche concerns to be aware of including fresh wind slabs, cornice fall and loose snow point releases. Also it's worth mentioning that a glide crack has opened up on Seattle Ridge and continues to creep open on Repeat Offender. Be aware of it and limit time below if you are near the up-track. 

Below 1,500' there is a LOW danger where triggering an avalanche is unlikely due to a snowpack consisting of hard crusts.

In Summit Lake, Girdwood, and near Johnson Pass triggering a deeper more dangerous avalanche near the ground is still possible but will be hard to trigger. If headed to Summit Lake please check out the weakly summary HERE.


Primary Concern

WIND SLABS: There was 3-6” of very light weight fluffy snow on all aspects throughout our region and a few inches fell overnight with warmer temperatures. This snow combined with Easterly ridge top winds 10-20 mph overnight with gusts into the 30s may have formed tender wind slabs on leeward slopes. The snow may feel "upside down" with slightly stiffer snow over softer snow. Look for areas of pillowed or drifted snow and watch for cracking. Pay attention to active loading this morning as few more inches are forecasted to fall with continued gusts into the 30s. 

LOOSE SNOW: Sluffs may also be easy to initiate on steep features and could be fast moving.

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? If skies clear this afternoon be aware of solar warming that may trigger loose snow avalanches in steep Southerly aspects.   

Terrain East of Sunburst with evidence of cornice fall in the background and obvious wind patterns on the snow. 

 

Cross-loaded slopes and the glide crack on Seattle Ridge south of the up-track. 

 

 


Secondary Concern

Yesterday the beautiful weather and soft snow inspired a number of folks to test some of the slopes around the advisory area. There were no reports of avalanches being triggered. However, it is important to remember today that there is still poor snowpack structure in many locations and the possibility of triggering a dangerous avalanche exists if you hit the wrong spot. It’s been a week since the Valentines Day storm dumped 2-3’ of heavy snow on top of a weak surface (surface hoar and/or near surface facets). Saturday was there were two human triggered avalanches on Seattle Ridge on this set-up. The good news is with time, the weak layer has been adjusting to the slab above, making it more difficult to trigger. However the consequences remain high, meaning it is still possible to trigger an avalanche large enough to bury, injure or a kill a person. Be aware that no red flags may be present (whumphing or cracking in the snow) and the pack could have a general "it seems fine to me" feel before someone finds a trigger point. Trigger points are often where the slab is thinner, near rocks or scoured areas. Also keep in mind, these slabs can break above you, release after several tracks are on a slope and be triggered remotely. The trickiest part about our current snowpack is how difficult it is to assess due to the spacial variability of both the weak layer, the slab, and even the bed surface in some places. Some steep solar aspects (S-SE) may have a slick sun crust bed surface/buried surface hoar combo. Be aware that snow pits and stability tests may not be representative of the actual slope you are trying to assess.

Buried surface hoar in a snow pit on Sunburst yesterday at 3750', SW aspect.

 

 


Additional Concern

At the bottom of the snowpack are various layers of facets with varying degrees of strength. In the Summit Lake zone and some areas in Girdwood Valley and Johnson Pass depth hoar has been found as well as some areas in Turnagain Pass. Last week's storm cycle tested these layers and only a few avalanches that we know of broke in them (Girdwood Valley, Portage and Summit Lake). These layers will be tough for people to trigger, but possible in shallow snowpack zones. The more likely case is where an avalanche occurring in the upper layers of the pack has the potential to step down and release the entire snowpack. If this does happen the volume will be large and could run long distances. 

 


Mountain Weather

Yesterday was clear, calm and cold for most of the day. Temperatures were near or below 0F at valley bottoms and around 10F at ridge tops. Winds were very light and northerly. High clouds moved in late in the afternoon and skies became obscured by the evening. Snow started falling and temperatures rose overnight. Winds picked up from the East blowing 10-20 mph with gusts into the 30s. 

Today will be mostly to partly cloudy with clearing forecasted in the afternoon/evening. Another 1-5 inches of snow is possible. East winds will continue in the 20s this morning and shift to become light and variable this afternoon. Temperatures will be in the 20Fs in the valleys and low teens in the Alpine.  Tonight will be partly cloudy. 

Tomorrow is forecasted to mostly clear with temperatures rising to the 30s. The next system is has the potential to impact the area Thursday evening into the weekend. There is some uncertainty about the timing and precipitation amounts and how warm it will be. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 12   3  .1 70 
Summit Lake (1400')  11  3  .2  34
Alyeska Mid (1700')  13  3  .1  66

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  7  ENE* 15* 37* 
Seattle Ridge(2400')  8 rimed  rimed   rimed

*Sunburst started recording wind data at 1 am. 

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

Subscribe to the Turnagain Area Avalanche Advisory:

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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