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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 17th, 2015 - 7:00AM
Expires
Fri, December 18th, 2015 - 7:00AM
Forecaster
CNFAIC Staff
The Bottom Line

The avalanche hazard is CONSIDERABLE above and below treeline today. It will be possible for snowmachiners, riders and skiers to trigger dangerous slabs up to 3 feet in depth on slopes at and above treeline. Below treeline, warm temperatures and the potential for rain on the snowpack will make it possible to trigger slabs 1-2′ thick and/or wet loose avalanches  in steep terrain.

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Thu, December 17th, 2015
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
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
Considerable (3)
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

There are a variety of potentially dangerous storm related issues today. Caution is advised travelling in avalanche terrain, these conditions warrant careful route finding and conservative decision-making. We received a 6-8″ of snow that started falling in late the afternoon yesterday. We have now received over 3″ of water equivalent in the past week, equating to over 3′ of new snow in the Alpine. With the snow available to transport, winds over the past two days have created slab conditions on leeward slopes. An observer reported cracking in the upper 18″ on Seattle Ridge yesterday and triggering a small pocket of wind slab. This set-up may be more developed today and easier to trigger. 

In addition, temperatures are rising and may result in an “upside-down” structure and instabilities within the new snow. This may be more pronounced in the lower elevation bands. This means there is the potential for both wind slabs from the wind loading and soft storm slabs from the warming trend of the storm.

The snow line may rise over 1000′ today resulting in rain on snow in the lower elevation terrain. This could add additional load and saturate the snow on the ground. Wet-loose avalanches may be possible.

Watch for Red Flags (signs of instability): cracking, whumpfing and recent avalanching are all signs that the snowpack is stressed. New snow and wind may be actively creating dangerous avalanche conditions today.

Additional Concern
  • 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

We have been continuing to monitor the layer of Near Surface Facets and Buried Surface Hoar since they were buried at the beginning of this stormy period. So far they have been unreactive. However, as the slab and the load on top of this layer continues to grow they are worth remembering. This is an added reason for caution today in avalanche terrain.

Weather
Thu, December 17th, 2015

Yesterday was overcast, snow started in the afternoon and continued overnight, depositing 4-8″ of snow. Northeasterly winds blew in the 20’s and gusted into the 40’s. Temperatures were in the 20Fs.  

Today snow is forecasted to continue in the morning transitioning to scattered snow and rain showers after noon. Temperatures will be in the high 20Fs to upper 30Fs. Winds will be Northeasterly 15-25 mph. New snow accumulation of 2 to 4 inches is possible today.  Snow showers will continue overnight into tomorrow.

The low in the Gulf in conjunction with the occluded front will continue the pattern of unsettled weather in the area for the next few days with next stronger pulse of moisture forecasted for the weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   7   .7   42  
Summit Lake (1400′)  20  2  .2 15  
Alyeska Mid (1700′) 27    4 .3   35  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  19 ENE    23  49
Seattle Ridge (2400′)  21  n/a n/a   n/a  
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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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