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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 14th, 2018 - 7:00AM
Expires
Sat, December 15th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

The avalanche danger is  MODERATE  in the Alpine and at Treeline where triggering a slab 1-3′ deep is possible in a shallow areas of the snowpack. In the Alpine triggering an isolated windslab or getting caught up in a loose snow avalanche is possible in steep terrain.  Avoid traveling underneath glide cracks.

Assess the snowpack as you travel, identify areas of concern and evaluate consequences.

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Fri, December 14th, 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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

Overnight ridgetop winds have picked up into the teens with some gust in the 20’s mph. In the alpine there’s over a foot of low-density snow available for transport and another 3-6” of new snow in the forecast today. Triggering an isolated windslab on leeward or cross-loaded features will be possible, especially if you see blowing snow. Otherwise mild weather and cold temps have been keeping all this new snow as light dry powder. Should you go into steep terrain, pay attention to how much new snow is falling and if winds are moving it around. Shooting cracks will be an obvious clue windslabs are tender. Feel for punchy or upside down  snow and keep in mind the consequences of the terrain should even a small rug get pulled out from underneath you. In areas where winds aren’t an issue loose surface snow could move faster and farther than expected. 

Shooting crack on a wind loaded terrain feature on a NW aspect of Tenderfoot yesterday at 2500′. 

 

Some larger fast moving point release sluffs were observed yesterday in steep terrain on Sunburst. 

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
This graphic depicts how likely you are to trigger avalanches or encounter natural avalanches while traveling on avalanche prone slopes. Unlikely means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. The chance of triggering or observing avalanches increases as we move up the scale. Certain means that humans will be able to trigger avalanches on many slopes, and natural avalanches should be expected.

Size of Avalanches
This graphic depicts the potential size and destructive force of expected avalanches. 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, large enough to bury or destroy vehicles and break a few trees, and large enough to destroy railway cars, buildings, or a substantial amount of forest. Historic avalanches are massive events capable of destroying villages and gouging or altering the landscape.
More info at Avalanche.org

No new avalanche activity has been reported in our forecast zone since a wet and windy storm ended last weekend. Yesterday dozens of tracks could be seen in steep terrain which is a good sign of increasing stability. With that said there remains some uncertainty around weak snow within older layers of the snowpack, especially in Summit Lake, in Crow Creek Valley and the Southern end of Turnagain Pass where a thinner snowpack exists. The mid-elevation band is also more suspect where the snow quickly transitions to shallower depths. Observations this week have found a facet/crust combo 1-2’ below the surface in the mid-elevations (2000’ – 2700’.) Whumpfing and reactive stability tests were observed on Tuesday on Magnum’s NW shoulder. Rotten faceted snow near the ground in Summit Lake  is also a concern especially with more snow expected over the weekend. Evaluated the snowpack and terrain as you travel and be aware that obvious clues like whumpfing or recent avalanche may not be present.

Snowpit on Tenderfoot shows a thinner snowpack where weak snow is sitting on the ground. 

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

The first glide cracks of the season were seen on Sunburst SW face under the weather station and another on the SW face of Tincan Proper. A glide crack is the snowpack being pulled by gravity downhill along the ground. They can release at any moment without warning and are usually not associated with human triggers. The best way to manage this hazard is to avoid being on or beneath any slopes with cracks opening up. 

Weather
Fri, December 14th, 2018

Yesterday: Skies were clear and sunny. Temperatures were in the single digits (F) in the upper elevations and teens (F) near 1000′. Winds were light and picked up in the evening from the East 10-15mph with gusts in the 20s mph. An inch of new snow fell in Turnagain Pass overnight and a trace in Girdwood.

Today:   Temperatures will gradually increase throughout the day into the mid-20’s at 1000′. Snow showers will start this afternoon with 3-6 € of snow possible and another 4-5 € overnight. East ridgetop winds are expected to be 10-15mph and build into the 20’s mph overnight.

Tomorrow: Temperatures will continue to increase into the mid-30’s (F) at sea level. Rain/snowline may be around 500′. Another storm is expected Saturday evening through Sunday morning. An active weather pattern is expected to persist into early next week.

*Seattle Ridge weather station anemometer has been rimed and not recording wind data.    

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 13   1   0.1   31  
Summit Lake (1400′) 7   0   0   9  
Alyeska Mid (1700′) 14   trace   0.07   17  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 4   ENE   7   31  
Seattle Ridge (2400′) 12   *NA   *NA     *NA    
Observations
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Date Region Location
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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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