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Avalanche Advisory

Turnagain Area Avalanche Advisory
Sunday, April 16th 2017 5:38 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The overall avalanche danger is MODERATE this morning and will rise to CONSIDERABLE on steep Southerly facing slopes this afternoon and evening. Wet slab and wet loose avalanches will be likely to trigger and natural 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 deep slab avalanche 2-5+' thick.  Watch for changing conditions. Avoid travel on or under cornices and give glide cracks a wide berth. 

 ***On steep Southerly slopes with a thin snowpack, such as where rocks are protruding the danger could trend towards HIGH = natural wet avalanches likely, human triggering very likely.  Avoid travel in Southerly avalanche terrain in the afternoon and steer clear of runout zones. 

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. 

MONDAY AVALANCHE OUTLOOK:
No avalanche forecast will be issued tomorrow, Monday April 17th. The avalanche outlook will be the same message tomorrow as for today due to continued warm and sunny weather expected.


 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
Special Announcement
  • The CNFAIC will begin wrapping up the season during the last 2 weeks of April. Starting Sunday April 16th, 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.

Avalanche Problem 1

Blue skies and warm days will continue to be the theme for today and into the workweek. As the mountains continue to heat up a bit more each day, they will become more and more dangerous. It is 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. Each night the re-freeze is a bit less and the melt phase is a bit longer, creating a longer period of heightened avalanche conditions. 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. 

Over the past few days many natural wet avalanches have occured. The activity looks to be starting around 12:00 pm and continuing into the evening hours, as late as 8 or 9pm. Natural avalanches were witnessed on the front and backside of Seattle Ridge, in Girdwood, in Placer and in Whittier on Friday. In the Lost Lake area several wet avalanches have been seen this past week. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope. 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.   

 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 (due to more warming but also because it's simply steeper).
  • 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 avalanches seen have been large enough to injure, bury or kill a person. Extra caution is advised. Natural avalanches are happening. Get Out of Harm's Way! 

     

Large wet slabs on the Southwest face of Cornbiscuit - released sometime over the weekend (4/15 or 4/16). Mike Davidson Photo.

 

Natural avalanche that occured Friday around 5:30 pm on Ragged Top mountain in Girdwood Valley, Southeast facing slope.


Natural wet slab avalanche in the Lost Lake and Snug Harbor zone from earlier in the week (Photo: Troy Tempel). This areas is out of our forecast zone, but it is the type of avalanche activity we have been seeing on Southerly aspects - including the Seattle Creek drainage.

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Avalanche Problem 2

On the shaded and cool side of the mountains (Northerly aspects) dry snow still exists. There are several weak layers anywhere from 2-5' below the surface. As folks venture out looking for "cold 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 deep slab. 

This problem is one of low probability but high consequence as these are large and potentially unsurvivable slides. As the snowpack continues to adjust, triggering will become more stubborn and less likely with time. Keep these point 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.
  • These slides can be triggered remotely, for example, from a ridge or bench on the top/side or below. 
  • 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

Additional Concern

Several small glide avalanches have released on Southeast facing Seattle Ridge and Eddies Ridge over the past few days. 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. 

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. 

Glide avalanches and glide cracks near the Seattle Ridge up-track. 


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Mountain Weather

Over the past 24-hours skies have been clear and winds have been light along the ridgetops, in the 0-10mph range from an Easterly direction. Temperatures were a bit cooler than yesterday, but are still warm, climbing from the 20's to the 50's at sea level and rising to the mid 30'sF along the ridgelines.

Today and Monday, we can expect very similar weather - bluebird. Winds should remain light from an Easterly direction and calm at times. Temperatures are expected to rise to the 50'sF at elevations below 2,000' and into the 30's and 40F along the ridgetops. 

This stretch of high pressure and clear sky days should extend into the coming workweek. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 40   66
Summit Lake (1400') 38  22 
Alyeska Mid (1700') 41  61 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 33  NE  10 
Seattle Ridge(2400')  No Data SE  15 

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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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