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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 19th, 2013 - 7:00AM
Expires
Fri, December 20th, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

Pockets of  CONSIDERABLE  avalanche danger may be found today.  Watch for areas with deeper storm snow and wind driven slabs.  Last night’s storm is clearing today, but residual avalanche danger will linger as our weak base adjusts to the new load.  

During the fading daylight yesterday afternoon a couple small natural avalanches were noted along the Seward Highway.  This was at the very beginning of the stormy weather.  

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Thu, December 19th, 2013
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
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
Moderate (2)
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

There was a lot of low density snow available for wind transport before this storm, and all the new storm snow came in cold.  Storm totals are in the range of 9-12 inches, with wind slabs probably reaching twice that depth.  Water content of the storm snow was around 0.6-0.9 inches (Snow Water Equivalent).

Wind was predominately from the East and Southeast at our Turnagain Pass ridgetop stations.  Expect the majority of wind loading to be on West aspects with crossloading on North and South.  

This cold storm should be compared to the one we got over the weekend.  In that storm we had a little more snow, but we saw a number of skier triggered avalanches.  We can expect the same today, with possible warning signs like whoomphing (collapsing) and shooting cracks.  Conservative decisions are justified today as the snowpack adjusts to the increased stress. 

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

Storm slabs and wind slabs will be the evident surface layers, but the weak interfaces that may fail today could be older and deeper.  The freezing rain crust was one of the most reactive weak layers from last weekend.  It may show itself again today.  Below that rain crust we still have well developed facets on the ground.  Fortunately, digging a full depth pit to look at all those layers is easy with our shallow snowpack.  

Weather
Thu, December 19th, 2013

Yesterday temperatures started a dramatic rise.  Portage had one weather station increase 56 degrees in the last 24 hours, from -25 F yesterday to 31 F this morning.  Ridgetop stations continue to read colder temperatures  – less that 20 degrees through the snowfall.

Snowfall and wind are the big news for us today.  Mid elevations in Girdwood and Turnagain Pass have about 9 inches of fresh snow overnight.  Wind was strong during the snowfall, reaching gusts to 64 mph on Sunburst and 56 mph on Seattle ridge.  

The blizzard warning for yesterday has expired, and the snowfall and wind are diminishing.  Some clearing this afternoon is expected.

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Riding Areas
Updated Tue, January 12th, 2021

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
Open
No parking in turnaround at end of the road near the outhouse.
Placer River
Open
Early season conditions exist, including thin ice on rivers, swamps and lakes. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Skookum Drainage
Open
Early season conditions exist, including thin ice on rivers, swamps and lakes. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Turnagain Pass
Open
Twentymile
Closed
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Primrose Trail
Open
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Summit Lake
Open

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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.