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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, April 1st, 2018 - 7:00AM
Expires
Mon, April 2nd, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A generally  LOW  avalanche danger exists in the core zone of Turnagain Pass, while areas on the periphery continue to trend from a  MODERATE  danger to a LOW danger. Triggering a hard slab avalanche 2-4′ thick breaking in old buried weak layers is unlikely, but not impossible. Areas of most concern are above 2,000′ and in shallow snowpack zones such as Girdwood Valley and South of Turnagain Pass toward Johnson Pass and Summit Lake. Pay attention to afternoon warming and give cornices a wide berth.  

If you are headed South of Turnagain Pass more snowpack information can be found on the  Summit snowpack and avalanche summary  

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Sun, April 1st, 2018
Alpine
Above 2,500'
Low (1)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Low (1)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

March has slipped by already, Easter Sunday is here along with April Fools’ Day and sunset tonight will be around 8:45pm. For anyone that has been out in the mountains lately, the snowpack is getting more and more tired; like a runner in the final mile of a marathon. Almost three weeks have passed since the last snow event. A refresh is needed, will it come? Possibly later this week, we’ll have to wait and see. What about springtime corn skiing? Sunshine has been strong but air temperatures have not been warm enough during the day to let it soften Southerly surface crusts. Slightly warmer temperatures today could help this.

There has been no weather for over a week that has contributed to avalanche danger and the snowpack continues to stabilize. The chances for triggering a deep slab avalanche are becoming more unlikely as the days go by. However, if you’ve been tuning in, you’ll know we have a very poor structure to the pack. Various weak layers sit 2-4′ below the surface and are composed of facets and buried surface hoar. There has been no known avalanche activity for 10 days and stability tests show high strength in the snowpack despite the poor structure. This all said, the mountains by nature are uncertain and our snowpack does have weak layers. There is the remote possibility someone could find just the wrong spot on just the wrong slope and trigger a large and destructive slab avalanche. This scenario doesn’t fit neatly into the danger scale as it is a low probability, high consequence situation. 

What to keep in mind:

–  Periphery zones such as Girdwood Valley and the South end of Turnagain Pass towards Johnson Pass, Lynx Creek and Summit Lake all have thinner snowpacks and therefore are more suspect for finding an outlier slab avalanche
–  Northern to Eastern aspects have a generally thinner snowpack
–  T
rigger points are often in thin areas of the snowpack near rocks or in scoured areas along ridges
–  As always, p
ractice safe travel habits and minimize exposure in avalanche terrain

Sunshine:
Be aware of warming later in the day on Southerly slopes, especially steep southerly slopes with rocks that will help heat up the snow around them, aiding in possible wet avalanche activity. As we gear up for a warmer day today, keep the afternoon warming on your radar! 

Deep Persistent Slab is challenging to fit into the danger scale when stability is increasing due to their potential size and already low probability of triggering. 

 

 

Suncrust is having a difficult time softening on Southerly aspects. This particular crust was found around 2,500′ by Allen Dahl on Corn Biscuit.

 


Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Watch out for cornices along ridgelines. It’s that time of year where cornices will begin to slowly warm during daytime heating, making them easier to break off. As always, give cornices plenty of space and limit exposure underneath them. 

These are great days to be exploring. Thanks to Troy Tempel for the photo below from the far side of the Seattle Ridge drainage on Saturday. This is looking East back at Seattle Ridge proper and Zero, -1 and -2 bowls from the Western side of Seattle Creek. Note the large cornices in the distance along Seattle Ridge.

Weather
Sun, April 1st, 2018

Sunny skies with thin high clouds were over the region yesterday. Ridgetop winds were light from the West (5-10mph) on the higher peaks. Temperatures were near 35F at 1,000′ and 25F along ridgelines. Temperatures have dropped to the teens in valley bottoms overnight but have remained warmer (mid 20’sF) at the upper elevations due to a warmer air mass that moved in.  Note the  increase overnight from teens to 21F at 4,200′at the Penguin weather station.  

Today, sunny skies and warmer temperatures are on tap. Ridgetop winds look to increase to the 10-20mph range and shift more Northerly during the day. Temperatures should warm to the mid 30’sF in valley bottoms and remain in the mid 20’sF along ridgelines. Colder air looks to stream back in from the North this evening at the higher elevations, dropping temperatures back to the teens.  

For tomorrow and Tuesday, mostly sunny skies, cool temperatures and windy off-shore conditions are expected. A chance for clouds and snow flurries may occur mid to late week as models show a low pressure developing in the Bering. Stay tuned.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27   0   0   76  
Summit Lake (1400′) 22   0   0   30  
Alyeska Mid (1700′) 26   0   0   71  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   W   8   19  
Seattle Ridge (2400′) 23   Variable   4   15  
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Riding Areas
Updated Fri, May 01st, 2020

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.