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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, December 15th, 2015 - 7:00AM
Expires
Wed, December 16th, 2015 - 7:00AM
Forecaster
Graham Predeger
The Bottom Line

With 6-12+ inches of snow falling on Sunday night/ Monday morning from sea level to ridgetops there is a MODERATE avalanche danger in all elevation bands today.   Storm snow instabilities and loose snow avalanches are the primary concern today and are most likely to be encountered in very steep terrain.

Ice climbers: Snowfall totals in Portage Valley have been verified at 12 € or more yesterday.   This is potentially more than a €œmoderate € avalanche problem for this user group given the extreme and complex nature of the terrain.    

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Tue, December 15th, 2015
Alpine
Above 2,500'
Moderate (2)
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
Moderate (2)
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

Observations from yesterday are pointing toward an overall snowpack that continues to adjust to this latest pulse of snow.  The weak snow above the Thanksgiving rain crust continues to show signs that it is gaining strength and didn’t prove to be a concern in our snowpits yesterday.  Keep in mind this set up though (see secondary concern below) and recognize that areas where wind loading has occurred, there will be more weight on this weak snow/ storm snow interface.  Large triggers such as a snowmachine could prove enough to tickle out a fresh storm slab or wind slab 2-3’ deep.

Skiers pushing into steeper, upper elevation terrain (above 3500’) may also find fresh wind slabs in the 2-3’ range as we had a short but strong wind event on Sunday night.  In areas protected from the wind and lower elevations, the surface is quite unconsolidated.  Generally with more snow on the northern end of Turnagain pass, loose snow sluffs will prove to be fast moving and high volume today, particularly in steep terrain (greater than 40 degrees).

CNFAIC forecasters are elated to be able to utilize snowmachines again as a forecasting tool after last winters “snow drought” at trailhead locations.  Here, Graham Predeger digs in to look at our current snowpack structure at 2400′ above 2nd Bowl (Jr’s bowl) on the backside of Seattle ridge. 

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

We will continue to track the Thanksgiving rain crust/ facet combo (and buried surface hoar layer) until it is buried more than 3 feet deep AND proves dormant.  Though not reactive recently, all the ingredients are present to bake that cake (2’+ storm slab/ weak snow/ stout bed surface).  For the moment, look at this avalanche problem as an additional reminder to maintain safe travel protocols, and ensure you and everyone in your crew is carrying proper rescue equipment and knows how to use it.

Weather
Tue, December 15th, 2015

Low-level fog persisted most of yesterday near sea level with broken clouds and partly sunny skies above about 500′.   The snowfall shut off early yesterday morning with no new precipitation added during the daylight hours.   Winds were calm (single digits) throughout the day and temps were in the 20’s from valley bottom to ridgetops.  

Today, temperatures are starting out slightly inverted, promoting valley fog, though with a weak pulse of moisture arriving mid to late morning, that should usher in easterly winds in the 25-40mph range at ridgetops and act to mix the air a bit.   We may see 1-3 € of snow falling from sea level and up, around the eastern Turnagain arm region with temperatures in the 20’s F at ridgetops and low to mid 30’s F at sea level.

More active weather is on tap through the workweek as another low pressure moves into the Gulf and begins to affect Kodiak as early as tomorrow.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0   0   39  
Summit Lake (1400′) 23   0   0    14
Alyeska Mid (1700′)  25  0 0    33

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 19   W    4 28  
Seattle Ridge (2400′) 20    N/A  N/A  N/A
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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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