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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Friday, April 14th 2017
Created: Apr 14th 5:41 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.
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; I know....already...! 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!

The Bottom Line

The overall avalanche danger is MODERATE and could rise to CONSIDERABLE on 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 possible. On steep Southerly slopes with a thin snowpack, such as where rocks are protruding, triggering a wet avalanche will trend more to likely. On Northerly aspects where dry snow exists, there is the possibility of triggering a deep slab avalanche 2-5+' thick. Cornice falls and glide avalanches are also possible.

***The mountains are heating up a little more each day. It will be 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! At some point the slow warm up in the snowpack will reach a tipping point and large wet avalanches should begin (the springtime 'shed cycle').

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, just for the sun to warm them up and turn hard crusts into slop later in the day. Hence, a LOW danger in the morning transitions to a MODERATE or CONSIDERABLE danger in the late afternoon - and even into the evening hours. A big thanks to Dan Koepke for sharing his story from Sunburst yesterday, where he talks about this exact experience; watching the snowpack warm up during the day and around 4:30pm a slab avalanche is triggered on a Southerly facing slope that runs to the valley floor. This slab was ~150' wide and broke 12-18" deep, it stepped down to the ground in places (we are very glad Dan was able to ski out of this avalanche). You can see his full report HERE.

Video of the Sunburst avalanche, wet snow debris in motion (lack of powder cloud). Note the older debris from last week on the left that becomes partially covered. (Koepke)


Photo of Sunburst avalanche crown, ~16" average in depth at the top before stepping down ~50' below the crown to near the ground in places. (Koepke)

 

WET AVALANCHES (Southerly facing slopes) - late in the day:

The Sunburst slide above is a good example of what kind of terrain (Steep Southerly) to avoid late in the day. Our snowpack consists of several weak layers of facets and buried surface hoar. Because of this, wet slabs are possible and having them step down to deeper weak layers is also possible. Wet loose snow avalanches have also been occurring, these have been relegated to steep slopes with a shallow snowpack so far. 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 high 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. 

SPRINGTIME SHED CYCLE?
This is when the whole snowpack becomes wet and begins to litterally ooze and slide off the mountains. So far there is still cold snow at the upper elevations; some thinner and lower elevations are 'shedding' however, such as the Southeast face of Seattle Ridge. We will be watching the snowpack and and air temperatures and talking about this in the future. 

 

The Southeast face of Seattle Ridge - this zone is typically the first area in Turnagain Pass to begin shedding its snowpack.

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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 noteable is the March 27 buried surface hoar; this layer was buried by 3-6' of snow during the 10-day April Fools storm. We have not seen or heard of any avalanche activity on this layer for 6 days now, but with warm temperatures and a 'persistent weak layer' present, 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.
  • 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 noteable results

Additional Concern

Two new small glide avalanches released on Southeast facing Seattle Ridge yesterday. 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. 


Mountain Weather

Bluebird skies with a very light ridgetop breeze from the West was over the area yesterday. Temperatures were again warm, up to 50F at 2000' and below and up to 40F along some ridgelines. Overnight, temperatures have cooled to the mid 20's at sea level and the upper 20's at the higher elevations. Ridgetop winds turned easterly and have picked up to the 5-10mph range since midnight. 

Today, another clear sky day is on tap. The Easterly ridgetop winds should remain light, 0-10mph. Temperatures again will climb to 50F around 2,000' and below while the breeze could keep upper elevations in the 30's F. 

The high pressure over the region looks to remain in place through the weekend. We could see a bit of cloud cover on Sunday, but warm springtime conditions will remain. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 40  69 
Summit Lake (1400') 35  23 
Alyeska Mid (1700') 40  62 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  34 18 
Seattle Ridge(2400') No Data   10

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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