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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 10th, 2015 - 7:00AM
Expires
Fri, December 11th, 2015 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

With up to a foot of new snow falling overnight accompanied by moderate winds, we have a CONSIDERABLE  avalanche danger above 1,000′. Natural avalanches are possible and  human triggered avalanches are LIKELY  on slopes over 35 degrees. These will be  most pronounced in wind loaded terrain where slabs 1-2′ thick have formed. The new snow has fallen on a VERY unstable base and is expected to have a difficult time bonding – this also includes slopes that are sheltered from the wind.

**Very careful snowpack evaluation, cautious route-finding and conservative decision-making is advised if traveling in the backcountry.  Patience will be key  if skies clear enough today for travel above treeline.

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Thu, December 10th, 2015
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

The GOOD NEWS:  A quick hitting snow event rolled through last night and has, so far, added 10″ of new snow at Turnagain Pass. Girdwood Valley has seen slightly less with 8″ overnight and Summit Lake much less, only 2-3″. When adding last night’s total to yesterday’s 2-4″, we have a 24-hour accumulation of 10-14″. This is “low density” new snow which is great news, but that leads us to the 2nd part of the story…

The BAD NEWS:  This new snow has fallen on a VERY weak surface with a hard bed surface below (see photo).  Although it’s only a foot of new snow, it will simply have a hard time sticking to the old sugary snow below. Adding to this, avalanches triggered could run far with the help of the hard bed surface underneath. In short, this is classic case for creating very touchy avalanche conditions. This means you are more likely than not to trigger an avalanche if you enter slopes over 35 degrees. The exception are slopes where the new snow is so unconsolidated that it is not forming a slab – in this case, large sluffs can be expected.

Things to watch for if you are headed out:

  • Stiff, harder snow over weak, softer snow
       –  Hand pits are good ways to assess how the storm snow is bonding to the older ‘faceted’ weak snow
  • Shooting cracks in the new snow
  • Whumphing, or collapsing of the new snow into the weaker snow below

Photo below is from yesterday of the ‘weak’ faceted snow that sits on top of a hard bed surface. Imagine a cohesive slab of snow 12″ thick sitting on top of this weak layer/bed surface combination – yep, that’s what we have this morning and it’s a problem…

Weather
Thu, December 10th, 2015

Yesterday’s light snowfall added 2-3″ before intensity increased overnight adding another 10″ at mid elevations. (Check out the Turnagain Pass Snow Stake by clicking this link!). Winds have been Easterly and moderate with Sunburst averaging in the 20’s mph overnight and Seattle in the teens. Temperatures have decreases slightly with the snowfall as well and are sitting in the mid-20’s F this morning on ridgetops.

Today we can expect snowfall to decrease and skies start to break. Winds should remain from the East in the 15-20mph range and temperatures in the mid 20’s F at the mid and upper elevations.

Looking to Friday night and weekend, a potent storm system is slated to arrive that could bring “incredible snow rates” to Turnagain Arm and Anchorage – see this NWS discussion HERE.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28   10   1   34  
Summit Lake (1400′)  29   2    0.2 13  
Alyeska Mid (1700′) 30 8    0.8 23  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 26   NE   16   44  
Seattle Ridge (2400′) 27   SE   10   22  
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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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