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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Tuesday, April 18th 2017
Created: Apr 18th 4:28 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.
 Show the Complete North American Avalanche Danger Scale
Special Announcement
  • The CNFAIC has started wrapping up the season. During the last 2 weeks of April we will issue forecasts on Sunday, Tuesday, Thursday and Saturday mornings until the end of the month. The Avalanche Center will close up shop on April 30th. We do however, always monitor/post any observations that come in all spring and summer - so please keep us, and the community, posted on any snow/avalanche information you may come across on your upcoming adventures!
  • We have stopped issuing our Saturday Summit Summary for the 2016/17 season. Click HERE for our Springtime Avalanche tips.
  • Hiking on summer trails (including the Byron Glacier trail, Turnagain Arm Trail a.k.a the bike path, etc).  Extra caution is advised during the afternoon and evening hours for trails that cross under avalanche paths. Avalanches possible at the higher elevations could send debris over snow-free hiking trails. 

The Bottom Line

The avalanche danger is MODERATE above 1000' On steep Southerly facing slopes in the afternoon and evening, triggering wet slab and wet loose avalanches will be possible as the sun heats up and softens Southerly aspects. Paying attention to aspect and time of day are crucial. On Northerly slopes, where dry snow exists, there is still a chance of triggering a deeper persistent slab avalanche 2-5+' thick.  Watch for changing conditions. Avoid travel on or under cornices and give glide cracks a wide berth. 

Below 1000' the avalanche danger is LOW. The wet snowpack has been draining and getting a solid freeze at night. Due to a stout crust triggering an avalanche is unlikely. It is still important to pay attention to runout from higher elevation terrain. 

WEDNESDAY AVALANCHE OUTLOOK:

No avalanche forecast will be issued tomorrow, Wednesday April 19th. The avalanche outlook will be the same message due to a similar weather forecast. 


Primary Concern

The natural avalanche activity slowed down as temperatures cooled Sunday and Monday and the freeze was more pronounced. Today and tomorrow it will still be important to pay close attention to how the warming is affecting the pack. We are in a melt-freeze cycle on Southerly slopes - hard frozen crusts in the morning, which turn to unsupportable mushy and unstable snow by the afternoon/evening. Choosing what aspect to travel on, paying attention to the time of day and how long the slope you are on has been exposed to direct sunlight are essential to staying out of trouble.  Zones with thin snowpacks have been particularly active where free water is interacting with old weak snow. Wet loose snow avalanches may also trigger deeper slabs.  Rocky areas that are absorbing more heat should be avoided.

 If heading out for a fun day in the sun keep these points in mind:

  • Once the snowpack becomes so wet it is unsupportable and 'punchy' to skis, snowmachines or boots - it's time to head to a cooler aspect. 
  • The steeper the Southerly slope, the more it will warm and the more dangerous it will be.
  • Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down. 
  • The recent wet avalanches seen have been large enough to injure, bury or kill a person. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope.

Temperature trend from late last week until this morning. The natural wet avalanche activity peaked during the warmest days Friday, April 14th and Saturday, April15th. 

 

Natural wet slab avalanche that occured on Friday afternoon on Seattle Ridge. 


Secondary Concern

Yesterday around 5 pm, a skier triggered a slide on a West aspect in Triangle Bowl on the backside of Seattle Ridge. The skier was the 4th person on the slope and triggered it in a thin spot. They were able to ski off of the slab. The bed surface was reported as the rain crust from the April Fool's storm. In this springtime transition it is important to remember on the shaded and cooler side of the mountains (Northerly aspects: NE - NW - W), a cold mostly dry snowpack still exists. Afternoon warming may also influence how easy it is to trigger weak layers that are buried anywhere from 2-5' below the surface. As folks venture out looking for "cold, soft snow" this remains a concern. Shaded aspects (NE - NW - W) in the mid and upper elevations that haven’t avalanched already are the most suspect places for triggering a deeper slab.  

This problem is one of low probability but high consequence as these are potentially large and unsurvivable slides.

Keep these points in mind:  

  • It will take someone hitting a 'thin spot' in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall.
  • There may be no signs of instability before the slope shatters 
  • Several tracks may be on a slope before it releases
  • Stability tests may not produce any notable results

Triangle Bowl a few minutes after the avalanche was triggered. Thanks to the party involved for sharing the photo and information.


Additional Concern

Several small glide avalanches have released on Southeast facing Seattle Ridge and Eddies Ridge over the past week. We expect this trend to continue with the warm days ahead. Keep an eye out for glide cracks, full depth cracks in the snow, and limit time underneath them. 

Glide cracks in Eddies continue to open. Glide avalanche occured on Wednesday April 12th. 

 

Cornices: Cornices are large and likely hanging close to their tipping point. Direct sunshine, a person, or a group of people on top these could be enough to cause one to break. An observer in Seattle Creek noted a large cornice fall on Friday. Cornice crevasses have also been noted (opening slots where the cornice is pulling away from the ridge but has not broken off. Give cornices a wide berth from above and limit exposure under them from below. 

Cornice in Summit Lake with old slab crown below. 

 


Mountain Weather

Yesterday skies were partly cloudy to mostly clear. Winds were light and Westerly. Temperatures were in the high 20Fs at upper elevations and 30-40Fs at lower elevations. Overnight temperatures dropped below freezing.

Today will be mostly clear and sunny. Winds will remain light. Temperatures will be in the 30-40Fs in the valleys and with high 20Fs to low 30Fs forecasted above 3000'. Tonight into tomorrow looks to be very similar with temperatures dropping at night and climbing back up during the day. Clouds may increase Wednesday evening. There is a pattern shift still in the forecast for the weekend. Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31   0 64 
Summit Lake (1400') 30  0 0  21
Alyeska Mid (1700')  32  0 0  58

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 25   3  9
Seattle Ridge(2400')  No Data  3   12

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
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
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