Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, February 16th, 2017 - 7:00AM
Expires
Fri, February 17th, 2017 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is CONSIDERABLE  above 1000′ around Turnagain Pass, Placer Valley and Girdwood due to a variety of concerns. Natural avalanches are possible and human triggered slab avalanches 3+’ thick are likely on slopes steeper than 35 degrees.  Fresh wind slabs and loose snow avalanches will also be easy to tigger and should the sun appear, these may release naturally. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential today.

Below 1000′ the avalanche danger is MODERATE where an avalanche from above is possible as well as triggering a loose snow avalanche.  

Summit Lake:  Expect the avalanche danger to remain elevated due to recent a recent storm that has impacted our region. Click  HERE  for the weakly Summit Lake Summary.  

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Thu, February 16th, 2017
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
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
Considerable (3)
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
  • Storm Slabs
    Storm Slabs
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

In the past 3.5 days Turngagain Pass has received 3.1 inches of water (SWE) and just under 4.0” SWE was recorded in Girdwood. This water weight (either as snow or rain) combined with strong winds caused a widespread natural cycle as well a variety of lingering avalanche concerns. Yesterday all three red flags were observed between Girdwood and Turnagain Pass in the afternoon as clearing skies allowed for a good look around. In addition to dozens of mid-storm avalanches observed, several natural slabs released in the afternoon in Girdwood. There was also a report of a remote triggered avalanche in the Girdwood Valley. Very loud collapsing (whumphing) was experienced in Turnagain Pass and upon investigation was caused by surface hoar collapsing 2-3’ below the surface. Heat from the sun caused numerous natural loose snow avalanches in steep terrain on South and Southeast aspects. Today expect similar conditions as more unsettled weather is expected to bring another 4-10” of new snow accompanied by Easterly winds averaging 15-25mph, enough to actively be loading leeward features. Although the sun is not anticipated today, should it appear, there is enough solar energy to make the following concerns easier to trigger. Be aware of the following recent storm snow instabilities:

Wind Slabs: Expect fresh wind slabs up to 1’ thick to be tender on leeward features today. It will also be possible to trigger an older, much deeper wind slab 3+’ thick on a variety of aspects. These wind slabs may be sitting on top of weak snow (buried surface hoar) and/or a slick bed surface (old sun crust on Solar aspects) and may propagate further than expected. 

Loose Snow Avalanches: Loose surface snow “sluff” will be easy to trigger, and may release naturally if the sun appears today.

Triggering a wind slab or loose snow avalanche will be likely today on slopes steeper than 35 degrees.  It is also important to remember natural avalanche are still possible. Avoid being in avalanche runout zones and remember that recent avalanches, cracking and collapsing (whumpfing) are obvious signs the snowpack is unstable. 

Natural avalanche activity over the last few days on the SE face of Seattle Ridge. There are still places like the slope above the uptrack that did not slide on this aspect. 

 

Cracking was obsevered on a steep unsupported test slope yesterday on Tincan, West aspect at about 2000′. 

 

Beware there is not a lot of info about the new snow/old snow interface, but there are places where wind slabs 3+’ thick are sitting on buried surface hoar and could propagate large avalanches. FYI – the two upper rain crusts in this photo were not found above 2000′, but the sun crust was observed in the upper elevations prior to this storm.

 

 

Avalanche Problem 2
  • 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

Cornices have been growing over the last few days due to strong winds and heavy snowfall. These may release naturally or with the weight of a person. If you are along a ridge, cornices can be difficult to see, and can break further back than expected. Avoid being under or above these very unpredictable and precariously perched features.

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

Weak snow (facets and depth hoar) in the lower layers of the snowpack continues to be a concern in our advisory area. Avalanches occurring in the upper layers have the potential to step down and release the entire snowpack in some places. If this does happen the volume will be large and could run long distances. As more and more weight is added to the snowpack this becomes more of a concern. A few of the naturals throughout this last storm looked to have run into older faceted snow. The possibility of these large avalanches is another reason for conservative terrain choices today. 

Sevearl natural slab avalanches on a SE aspect of Fishes Breath in Girdwood Valley, including one that stepped down into an older layer of the snowpack. Photo courtesy of Mike Welch

 

Weather
Thu, February 16th, 2017

Yesterday morning 6 € of new snow fell before 9am at all elevations. By late morning skies were clearing and remained partly cloudy for most of the afternoon. With the exception of solar warming felt on South and East aspects, temperatures remained below freezing most of the day. South winds shifted to more of an Easterly direction late morning and average 15-25mph with some gusts in the 40’s by early evening. Overnight an additional inch of snow was recorded.

Today expect mostly cloudy skies and scattered snow showers throughout the day. Temperatures are expected to hover around 32F near sea level and an additional 4-10 € of snow (up to .5 inches of water/SWE) is possible today. Easterly ridge top winds are expected to average 15-25mph with gusts in the 40’s mph. An additional 5-12 € of snow is possible this evening.

Similar weather is expected to persist over the next few days and into the weekend with a continued pattern of scattered snow showers and temperatures remaining below freezing (32F.)

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   1   .1   73  
Summit Lake (1400′) 26   1   .1   27  
Alyeska Mid (1700′) 27   5   .44   67  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18   ENE   18   54  
Seattle Ridge (2400′) 22   n/a   n/a     n/a    
Observations
Recent Observations for Turnagain Pass
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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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