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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, December 31st, 2014 - 7:00AM
Expires
Thu, January 1st, 2015 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The danger rating today is CONSIDERABLE in the Alpine for wind slab avalanches up to 2-4′ thick.  These will most likely be found below ridge-tops, on leeward aspects or along gullies due to cross-loading.  Conservative route finding and careful snowpack evaluation is recommended if venturing into steep terrain.

At treeline (below 2500′) the danger is MODERATE. Small isolated wind slab avalanches are possible on wind-loaded slopes on all aspects. Avalanches are more likely to be triggered in the Alpine on steep terrain features and have the potential to run into this elevation band. Avoid being under sustained steep slopes and be aware of people above you.  

There is still very little snow below 1000′. However it is possible for debris from an avalanche above to reach our lowest elevation band, as seen in some gullies along the Seward Hwy during the storm. The danger rating today is  LOW, but could return to No Rating if upper elevation conditions stabilize.  

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Wed, December 31st, 2014
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
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
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

During a 60-hour period, ending last night, sustained ridge top Easterly winds averaged in the mid 40’s mph with gusts as high as 88mph. We estimate snow totals to be around 12-16” in upper elevations, but unfortunately it is impossible to calculate since much of this snow has been blown away. Yesterday visibility was poor and conditions were too dangerous to access the alpine thus we don’t have much information about how the snow was loading on large steep terrain. We suspect wind slabs could be as thick as 4-5’ on leeward terrain features and below ridge tops. It is uncertain how easily a wind slab could be triggered in the Alpine today.

At mid elevations (2000 – 2800’) we did find wind slab pockets up to 2’ deep alongside large scoured slopes. We did observe these pockets to be loading low on features and well below scoured ridges. 

The storm’s predominant wind direction was from the East, but due to variable terrain features and very high mid-slope winds all aspects are suspect of wind slabs. You will most likely find isolated pockets at mid elevations and larger pockets on leeward aspects at higher elevations. Safe travel can be found on wind scoured slopes and ridges – which will be obvious, based on their rough texture and signs of old eroded ski tracks.

If you venture into the Alpine stay on scoured ridges and avoid steep terrain with hard, smooth, pillow-like features. Listen for hollow sounds and look for shooting cracks, but realize that wind slabs have a tendency to break once you are well onto the slab. It is best to avoid steep slopes that could be wind loaded until the snow has a chance to stabilize. 

Luckily, this is the type of snow condition that heals quickly as long as temperatures are cool and we don’t see any additional precipitation and wind loading. Cooler temps could also help improve the quality of the riding. Yesterday was quite variable above 2000’. 

Additional Concern
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

We have been tracking a buried surface hoar layer since Dec.18th when a skier triggered a large avalanche on Sunburst.  There has also been some recent concern of weak faceted snow in thinner areas of our snowpack in Girdwood and Summit Lake. As of the last 48 hours, we do not know of any recent natural avalanche activity occurring on old buried weak layers. There is just enough concern that a human could tip the balance or if a wind slab could step down to keep persistent slabs in the forefront of our minds. We suspect a slab if triggered at this layer could be as deep as 4-6’ in some upper elevation locations. It is best to avoid steep slopes today and let buried weak layers adjust to its new load.

Weather
Wed, December 31st, 2014

Over the last 72 hours we have had sustained Eastern ridgetop winds in the 40’s mph with gusts into the 80’s.  Winds have decreased considerably overnight.  Precipitation has been relatively moderate with storm totals 12 -16 € at higher elevations and up to 6 € at the road elevation on the Northern side of Turnagain Pass. Temperatures increased from the mid 20’s F to mid 30’s F, and rain line fluctuated between 500ft to 1300ft throughout this two-day storm.  

Today, light snow accumulation, up to an inch, is expected into the early evening. Temperatures should decrease into the mid 20’s F in upper elevations and, and moderate ridgetop winds look to be shifting and coming from the South.

Clear skies are forecasted for New Years Day with temperatures in the 20’s F. Strong Northerly ridgetop winds (30 – 40mph) are expected again in Turnagain Pass on Thursday and into Friday.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   trace    0.1 35  
Summit Lake (1400′) 33   trace    0.1 7  
Alyeska Mid (1700′) 33   1    0.4 27  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   E   30   85  
Seattle Ridge (2400′) 27   E   26   65  
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Riding Areas
Updated Mon, October 26th, 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
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Turnagain Pass
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Carter Lake
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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.