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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Saturday, April 15th 2017
Created: Apr 15th 4:25 am
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.
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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.

The Bottom Line

The overall avalanche danger is MODERATE in the morning but will rise to CONSIDERABLE and maybe go to HIGH on steep Southerly facing slopes later this afternoon and evening. As the sun heats up and softens solar aspects during the day, triggering a wet slab or wet loose avalanche will be likely and naturals are possible. Paying attention to aspect and time of day are crucial. On Northerly aspects where dry snow exists, there is still the possibility 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. 

 ***The mountains are heating up a little more each day. It is important to pay close attention to how the warming is affecting the snowpack. If you see any avalanche activity today or over the weekend please let us know!  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 are still possible at the higher elevations that could send debris over snow-free hiking trails. 


Primary Concern

Timing is everything...

It's that time of year where clear skies freeze up the snow surface at night and then the sun and warm air temperatures turn hard crusts into slop later in the day.  A MODERATE danger in the morning transitions to a CONSIDERABLE or even HIGH danger in the afternoon and into the evening hours. Choosing what aspect to travel on, paying attention to the time of day and how long the slope you are playing on has been exposed to direct sunlight are essential to staying out of trouble. Remember to avoid the runout areas of Southerly slopes as well as things heat up. 

Yesterday observers saw natural wet avalanche activity start around 12:30 pm and continue into the evening on Southerly slopes. Natural avalanches were witnessed on Seattle Ridge, in Girdwood, in Placer and in Whittier. A large skier triggered avalanche occurred on Sunburst on Thursday on a Southerly slope. This stepped down to the ground. Wet activity has been observed all week on Southerly slopes and 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 in mind these things:

  • 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. 

All of the avalanches in the pictures below are large enough to injure, bury or kill a person. Extra caution is advised. Natural avalanches are happening. Get Out of Harm's Way! 

Sunburst avalanche that was triggered around 4:30 pm on Thursday afternoon.

Natural avalanche on Seattle that was witnessed around 4 pm yesterday. Avalanche path in center of photo that has dirty debris. 

Natural that occured yesterday around 5:30 pm on Ragged Top mountain in Girdwood.

Wet loose that triggered wet slabs and ran to the ground on Corbiscuit. Photo: APU Snow Science Class


Secondary Concern

On the shaded and cool side of the mountains (Northerly aspects) dry snow still exists. While wet snow issues are not a problem here, deep slab issues are. There are several weak layers anywhere from 2-5' below the surface. The most notable is the March 27 buried surface hoar and/or facets; these layers were buried by 3-6' of snow during the 10-day April Fools storm.  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

Small glide avalanches have released on Southeast facing Seattle Ridge the past couple days. On Wednesday a larger glide released on the South aspect of Eddies ridge. 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. Most cracks appear to be small and in areas less traveled, but a glide avalanche can also release with little warning when a crack is not visible prior. 

Cornices: Cornices are large and likely hanging close to their tipping point as the warming trend continues. 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 large cornice cracks/crevasses along some of the ridgelines. Give cornices a wide berth from above and limit exposure under them from below. 

 

Glide avalanches and glide cracks near the Seattle Ridge uptrack. 

 


Mountain Weather

Yesterday was another warm spring day with clear, blue skies and warm temperatures. Highs were in the 40-50Fs and winds were light and variable. Temperatures dropped just below freezing last night and winds stayed calm. 

Today looks to be very similar with temperatures in the 30-40Fs at higher elevations and 40-50Fs at lower elevations. Skies will be mostly clear today and it will be partly cloudy tonight with temperatures in the low 30Fs. 

The current pattern is forecasted to continue until Thursday or Friday next week with a low-pressure system moving into the Gulf and bringing precipitation to the area. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 42  67 
Summit Lake (1400') 35 23 
Alyeska Mid (1700') 40 0 61

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  35  SW 12 
Seattle Ridge(2400')  No Data  SE 6 13 

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: Dec 08, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedRain and snow have fallen in Turnagain Pass this week, but not enough to open for snowmachining. Continue to check back to this site for updates.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to 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.


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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