Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, January 28th, 2017 - 7:00AM
Expires
Sun, January 29th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  CONSIDERABLE  on upper elevation slopes where triggering an avalanche on a persistent weak layer or a  wind slab 2-3′ thick is likely and cornices are suspected to have grown large and be tender.  Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential today.  At Treeline and below  the danger will be  MODERATE  where triggering an avalanche on a persistent weak layer will still be possible.  Practice safe travel protocols, always carry rescue gear and please let us know what you see out there!!!  

Girdwood Valley:  Slabs have the potential to be larger due to more snow that has fallen on a weaker snowpack compared to Turnagain Pass. Avalanches were running to the ground during the storm.  

Summit Lake: Dangerous avalanche conditions exist.  Please check out the Saturday Summit Summary  HERE.  

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Sat, January 28th, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
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

As we got a few patches of visibility over the past two days we have been able to see evidence of the natural avalanche cycle that occurred during the storm and were reminded of the variability of the snowpack across the advisory area. In Girdwood Valley some avalanches were running to the ground on basal facets that formed early in the season. A similar weak layer is also the suspected culprit in a number of large avalanches that ran in the gullys at the southern end of Seattle Ridge.  At lower elevations in Turnagain Pass there were signs that avalanches were running on the January 13th layer of buried surface hoar. All these persistent weak layers still need time to adjust to the heavy load they received and could be triggered today. Shallow areas in the snowpack will be the most likely trigger spots. Be on the lookout for cracking and collapsing and areas where you can feel weak snow below strong snow. Do not overload steep slopes with multiple skiers or snowmachines on the slope at the same time! 

Yesterday at lower elevations it was easy to find the rain/snow line around 1400′. Water had formed two layers below the surface that were slowly cooling and may have formed crusts overnight. If these are solid today the likelyhood of triggering the January 13th buried surface hoar will go down. If the upper snowpack is still wet, persistent slabs may still be possible. 

Seattle Ridge South, both the gully and the face slid. Road obs yesterday showed that most of the gullys in this area slid and some made it all the way to the creek. 

 

Slab in above Tincan Gorge. Supected weak layer Janurary 13th buried surface hoar. Photo: Joe Kurtak

Snowpit on Tincan at 1100′, shows the layers of wet snow and the January 13th buried surface hoar

 

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

Strong easterly winds during the storm quickly moved snow, loaded slopes and triggered natural avalanches. Probing around a minor ridge yesterday showed that the winds had definitely redistributed snow. The windward side had less than a meter of snow and leeward side had over 2 meters. There was wind features in all of the Alpine terrain that was visible. Today wind slabs 2-3′ thick are likely on steep leeward slopes. It will be important to look for pillowed or drifted areas and watch for shooting cracks. These slabs may allow you get out onto them before they break. There is still snow available for transport today and the winds are shifting to the west. Pay attention to changing conditions if you see blowing snow and slopes being actively loaded.

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

Warm wet snow and strong winds are notorious for cornice growing. We have had limited visibility into the Alpine but suspect they will be looming over much of the leeward terrain. Give cornices wide berth, avoid travel on slopes below and remember they can break farther back onto the ridge than expected.  If they do break and fall they could trigger an avalanche on the slope below.

Weather
Sat, January 28th, 2017

Yesterday was mostly cloudy with snow showers throughout the day. Easterly winds were light with a slight uptick in the evening with gusts in the 20s. Temperatures were in the 30s at valley bottoms and 20s at ridge tops. There was a slight cooling trend overnight.  

Today will remain cloudy with snow showers forecasted throughout the day. Accumulations will be minimal. Temperatures will be slightly cooler than yesterday. Winds will be westerly 10-20 with gusts into the 30s. Snow showers diminish overnight but cloudy skies and a chance of snow remains through the weekend.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  32 1    .1  61
Summit Lake (1400′)  30  1  .1  27
Alyeska Mid (1700′)  30  2  .2 57  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  21 ENE   10   31  
Seattle Ridge (2400′)  24  rimed rimed   rimed  
Observations
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Riding Areas
Updated Mon, December 02nd, 2019

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
Closed.
Placer River
Closed
Closed.
Skookum Drainage
Closed
Closed.
Turnagain Pass
Closed
Closed.
Twentymile
Closed
Closed.
Seward District
Carter Lake
Closed
Closed.
Lost Lake Trail
Closed
Closed.
Primrose Trail
Closed
Closed.
Resurrection Pass Trail
Closed
Closed. Will be open for the 2019/20 season pending adequate snow cover.
Snug Harbor
Closed
Closed.
South Fork Snow River Corridor
Closed
Closed.
Summit Lake
Closed
Closed.

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