Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, December 31st, 2016 - 7:00AM
Expires
Sun, January 1st, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

A  CONSIDERABLE  avalanche danger exists in the mountains surrounding Turnagain Pass and Girdwood Valley  on all slopes out of the trees. Human triggered wind slabs are likely on leeward and cross loaded slopes. It will also be possible to trigger a slab 2-3′ thick on older buried weak layers.  

In sheltered areas a  MODERATE  danger exists where triggering a slab avalanche 1-3′ thick that breaks in older snow, remains possible.  

A  LOW  avalanche danger exists below 1000′ and triggering an avalanche is unlikely.  

Johnson Pass region: A shallower snowpack exists in the mountains South of Turnagain Pass. We have limited snowpack information for this area  – if you are headed this way, a  conservative mindset is recommended  along with easing into terrain. Triggering a slab avalanche is possible and could be triggered from below.

Please check the Summit Lake Summary HERE. There was a natural wind slab avalanche cycle yesterday in that area.  

Don’t let the sunshine and holiday weekend lure you into making poor decisions. The snowpack is complicated and cautious route finding is recommended! Pay attention to other groups and practice safe travel protocols.  

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Sat, December 31st, 2016
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

Yesterday wind plumes and moving snow were seen throughout the day. There was a solid 12 hr period of wind speeds 30 mph and above. Seattle Ridge reached a peak gust of 75 mph at 6pm last night. The NW winds again were channeled due to terrain, loading or stripping a variety of aspects.  As noted yesterday the flow direction is known to load Easterly slopes on Seattle Ridge, such as Repeat Offender. On the East side of Turnagain Pass, this flow often loads Northerly slopes on ridgelines such as Tincan, Sunburst and Magnum as it blows from the south through Turnagain Pass. Yesterday there was limited natural avalanche activity in the core area of Turnagain Pass with a few new wind slabs being observed in Cornbiscuit and Zero Bowl. There were also two small snowmachine triggered wind slabs as well. Observers reported cracking and slab conditions well below treeline. 

Today wind slabs are likely to be triggered in leeward or cross loaded areas. Due to the strong winds look for pillowing farther down slope and avoid hollow sounding snow. Wind loaded slopes will be suspect and triggering a slab will be more likely in thinner areas of the snowpack near rocks or where the snow transitions from a ridge to a steeper slope. Wind slabs have the potential to allow you out onto them before they break. Look for cracking and keep in mind that wind loaded slopes could overload buried weak layers and a wind slab avalanche could ‘step-down’, triggering a larger slab avalanche.

Summit Lake saw a wide-spread wind slab natural avalanche cycle yesterday. Areas south on Turnagain Pass such as Petes N and S as well as Johnson and Lynx may be similiar and more sensitive today due to a shallower snowpack. 

Wind transport on Lipps Ridge, note the wind scouring and wind scalloped surfaces. 

Wind slabs in N Cornbiscuit Chutes. Photo: Heather Thamm

 

 

Avalanche Problem 2
  • 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

The snowpack in the advisory area is complex. Most terrain harbors weak snow under a slab from the past two weekend storms. Winds have moved snow around in open areas and snowpack depths are variable. The weak layers under the slabs are notorious for creating dangerous avalanches conditions for extended periods of time after storms end.  Both buried surface hoar and facets are present. There are areas adjacent to those that slid during last weekend’s storm that may still have the potential to go today. It is important to remember thinner areas are often the place that old weak layers are initiated. It may be harder to initiate but the slides could be large and deadly. Avalanches may run to the ground. The Lipps skier triggered slide that occurred Thursday afternoon was a persistent slab that broke in weak faceted snow 1-2′ below the surface. 

Today it is important to pay attention to:

  1. Whumpfing / collapsing
  2. Cracking in the snow
  3. Hard stiff snow over softer old sugar snow
  4. Thin areas of the slab – these are likely trigger points
  5. REMEMBER PERSISTANT SLAB AVALANCHES can occur when no signs are present as well – more reasons to follow safe travel protocols.

As you choose terrain to ride or ski today, think about how large and connected it might be. It may not be the 1st snowmachine rider or skier onto the slope that triggers it. Triggering a deeper persistent slab is possible and winds from yesterday may have added stress/load.

Skier triggered avalanche on Lipps, 12.29.16. Full report HERE.

 

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

Expect cornices to be sensitive and easy to break off. They also could trigger a slab avalanche below. Be extra cautious near ridgelines today where cornices can be challenging to navigate.  If you suspect a corniced ridge give these a wide berth and be aware of people below you. Due to the unsusal wind loading yesterday look for new cornices or unsual loading patterns. 

Weather
Sat, December 31st, 2016

Wind was the main event yesterday with steady NW winds blowing 30 mph and gusting to 75. These were more southerly depending where you were on Turnagain Pass. Terrain effect on the winds was highly variable. Temperatures were in the 20Fs and skies were broken. Overnight N winds were 15-25 gusting into the 30s. Temperatures were in the mid 20Fs and skies were mostly clear.  

Today will be mostly sunny with temperatures in the 20Fs and light N-W winds. Tonight will be partly cloudy with cooler overnight temperatures dipping into the teens and light SW winds.  

Tomorrow (2017) and into the week should be clear and slightly cooler due a “strong blocking ridge” creating a “prolonged period of dry weather over Southcentral Alaska.”

PRECIPITATION 24-hour data (6am - 6am)
  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25    2 ** .4**   41  
Summit Lake (1400′)  24 0    0  12
Alyeska Mid (1700′)  25 0    0  27

 **possible wind effect at SNOTEL site

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) Under repair   Under repair      Under repair    Under repair  
Seattle Ridge (2400′) 21    NW 30   75  
Observations
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Riding Areas
Updated Wed, December 11th, 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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