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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
Fri, February 20th, 2015 - 7:00AM
Expires
Sat, February 21st, 2015 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

Today in the Alpine the avalanche danger is CONSIDERABLE where a slab 1-3′ thick is sitting on a weak layer of old snow. This weak layer has been reactive over the last few days and is likely to be triggered on terrain steeper than 35 °. Below 2000′ the avalanche danger is MODERATE where a more stable snowpack structure exists.

Weather in the form of high winds will be arriving today as another low-pressure system moves into the Southcentral region.   Precipitation is expected to intensify into Saturday and will likely increase the avalanche danger for tomorrow.  

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Fri, February 20th, 2015
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
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
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • 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

Today we will see the first of this weather pattern shift as East winds increase, possibly as high as 30-40 mph along ridgetops. With only a few inches of snow available for transport wind loading could add additional stress to an already reactive weak layer. 

Above 2000’ a weak layer of faceted snow is present beneath a 2’ slab in Turnagain Pass that was laid down four days ago. On Tuesday several remotely triggered avalanches occurred on the South face of Tincan as seen in the photo below. Collapsing has been the most commonly observed (heard) sign as this weak layer adjusts to its load. Over the last few days many test pits have been performed and continue to show propagation potential with moderate results.

In areas outside of Turnagain Pass a similar (SLAB + WEAK LAYER) problem exists. In Summit Lake the average slab depth is closer to 1’ in the alpine. Click HERE to see a video from yesterday at Manitoba. In the upper elevations of Girdwood this slab is estimated to be closer to 3’ thick.

Travel advice today is very simple. Avoid all slope angles greater than 35° including small steep features with terrain traps below. With high winds and poor visibility expected today this should be easy advice to follow. 

This is a view of Tincan’s South face as seen from along the Seward Hwy. These three avalanches were remotely trigged on Feb.17, the day after a storm left 2′ of snow in the upper elevations of Turnagain Pass. If you look closely you will notice recent ski tracks on Common bowl avoid the steepest convexed rollover. 

Avalanche Problem 2
  • 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

If winds increase as forecasted today small wind slabs 4-6” could be found at mid elevation near treeline. This is a secondary problem to the persistent weak layer + slab combo described above and travel advice remains the same. 

Weather
Fri, February 20th, 2015

Yesterday skies were sunny and temps reached the low to mid 30’s F at lower elevations. Upper elevations remained slightly cooler with localized light winds 5-15mph from the Southeast.

Overnight temperatures have remained elevated in the low 30’s F at lower elevations and high 20’s F along ridgetops. Winds have steadily increasing 15-35mph out of the Southeast on Seattle Ridge and no new precipitation has been recorded in Turnagain Pass.

Today ridgetop winds are expected to be out of the East (30-40 mph) as another warm low-pressure system moves into the Southcentral region. Temperatures will be in the mid to high 30’s F at sea level, with light precipitation starting this afternoon into the evening. Rain/snow line could be as high as 1500′.

Tonight strong winds (40-50 mph) will continue out of the East in Turnagain Pass. Precipitation will increase with up to an inch of water (rain) expected for Saturday at sea level. Temperatures could reach the low 40’s F and rain/snow line may be as high as 2000′.    

*Seattle Ridge weather station wind data was only available after 3PM on Feb.19.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   0   0   42  
Summit Lake (1400′) 24   0   0   8  
Alyeska Mid (1700′) 32   .01   trace   25

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27   N/A   N/A     N/A    
Seattle Ridge (2400′) 28   *SSE   *15   *35  
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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
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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.