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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
Sat, December 15th, 2018 - 7:00AM
Expires
Sun, December 16th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is  MODERATE  in the Alpine and Treeline. A bump in easterly winds today along with a few inches of snow this morning will likely form fresh wind slabs, up to a foot thick, that could be easy to trigger. If snowfall and wind intensify more than forecast, the danger will rise to CONSIDERABLE. Additional concerns: watch your sluff, as these have been getting larger, and keep an eye out for glide cracks and avoid traveling underneath them.

SUMMIT LAKE:   New snow overnight may overload weak layers near the ground, increasing the chance a person could trigger a larger slab avalanche.  

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Sat, December 15th, 2018
Alpine
Above 2,500'
Moderate (2)
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
Moderate (2)
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
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Watch for changing conditions. Ridgetop winds have picked up and should be blowing the existing loose surface snow into sensitive wind slabs this morning. These fresh slabs are likely to be shallow, around a foot thick, and easy to recognize if you are looking for them. Watch for areas with wind deposited snow and loading patterns in general. Shooting cracks will be an obvious clue wind slabs are tender. Feel for punchy or upside down snow and keep in mind the consequences of the terrain should even a small slab pull out from underneath you. In areas where winds aren’t an issue loose surface snow could move faster and farther than expected. 

Trevor Grams sent in this photo from the Library area further back along Tincan Ridge yesterday. Note the loose surface snow available for transport with today’s winds. 

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

As is often the case, the snowpack in the periphery zones of our advisory area such as, Crow Pass and Summit Lake have a shallower snowpack. In these areas, and even those closer to Turnagain Pass itself, we are tracking buried layers of facets and crusts that sit 1-2′ under the snow surface. These layers are most prevalent in the mid-elevations (2000’ – 2700’) and though snow pit data and a lack of avalanche activity has been pointing to an unlikely chance for an avalanche releasing deeper in the pack, additional snow load in the Summit area could start to tip the balance. Evaluate the snowpack and terrain as you travel and be aware that obvious clues like whumpfing may not be present.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks are beginning to open up in many places, including Sunburst’s SW face under the weather stationSW face of Tincan Proper, Gold Pan area (behind Cornbiscuit/Magnum) and the one shown below in the Johnson Pass area. These cracks can release at any moment, as this one did below in Johnson Pass. They are not associated with human triggers and the best way to manage the hazard is to avoid being on or beneath slopes with cracks. 

 

Photos of the Johnson Pass area glide avalanche couresy of Matt McKee.

 

An unnamed longtime CNFAIC pro observer puts his take on this avalanche problem…

Weather
Sat, December 15th, 2018

Yesterday:    Overcast skies were over region yesterday. Evening snow showers favored the Summit Lake area on the Kenai and further South where 4-6″ fell along the Seward Highway. Turnagain Pass and Girdwood only picked up 1-2″. This storm also favored the Anchorage region and North with 4-6″. Ridgetop winds have remained easterly in the 10-20mph range with gusts in the 30’s. Temperatures warmed dramatically overnight and are sitting in the teens along the ridgetops and 20’s at 1,000′.  

Today:  Snow showers have picked up this morning in Portage Valley and Girdwood. This quick moving front should give the mountains 2-4″ of snow before moving out by midday. Ridgetop easterly winds have picked up as well and should stay in the 15-25 mile range with gusts in the 40’s. Temperatures continue to rise and are expected to hit the upper 20’s at 3,000′ and mid 30’s at sea level.

Tomorrow:    What looks like a stronger front associated with the low-pressure in the Gulf moves in on Sunday. This should give the Turnagain area another chance to build up the snowpack. Warmer temperatures could bring a rain/snow mix to sea level, but so far it looks like it will be all snow at 1,000′. Stay tuned!

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 20   1   0.1   30  
Summit Lake (1400′) 18   4   0.5   13  
Alyeska Mid (1700′)  21 3   0.3   17  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14   ENE   14   41  
Seattle Ridge (2400′) 20   *no data   *no data     *no data    
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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
Closed
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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.