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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Tue, January 9th, 2018 - 7:00AM
Expires
Wed, January 10th, 2018 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  MODERATE  on all slopes above 2,000′ in elevation, where triggering a slab avalanche, breaking 1-3′ deep on a weak layer of snow is possible. Slabs may release after several tracks are on the slope and avalanches may be triggered remotely.  Additionally, triggering a larger slab breaking near the ground remains possible at elevations above 3,000′.

The danger is  LOW  near 2,000′ and below.

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Tue, January 9th, 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
  • 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

Above ~2,000′ our concern is the New Year’s storm snow that has now settled into a slab, around 12 – 20″ at Turnagain Pass and 20-30″ in the Girdwood Valley.  We have the buried surface hoar that was the cause for last week’s avalanche activity that sits right under this New Year’s snow. Could this slab/weak layer combination be triggered by the weight of a skier or snowmachiner? The answer is still YES. The buried surface hoar layer is slowly gaining strength and the slab is becoming more stubborn to trigger. However, snow pit results are still showing this layer to be reactive and to propagate – meaning human triggered slabs are possible if one hits the wrong spot on the slope. In addition, we are also concerned about slopes that avalanched in early December which have a thinner snowpack and harbor facets under the slab. Observers yesterday dug in a thinner spot on Sunburst and found reactive facets near the ground. 

On January 2nd it rained up to 2,000-2,300′, creating melt-freeze crusts in the upper snowpack at these elevations and below, making triggering an avalanche unlikely in lower elevation terrain.

For those riders and skiers headed out today:

  • Keep in mind that travel in the upper elevations is where triggering a slab is most likely. This is above 2,000′ where NO crusts exist in the top foot of the snowpack.
  • Remotely triggering a slab is possible, several tracks may be on the slope before a slab releases and no signs saying ‘the slope is unstable’ are likely to be present.
  • Larger slopes are more suspect as well and those with rocky features.
  • Safe travel habits are always key, but especially when dealing with persistent and deep persistent slab avalanche problems: expose only one person at a time, have an escape route planned, watch your buddies closely and view all slopes as avalanche paths. If the snow does slide where will it go? Avoid terrain traps. 

 Wendy’s video and photo from 3,000′ on Sunday illustrate our current buried surface hoar issue well: 

Thin snowpack at 3400′ on Sunburst. Note the weak faceted snow at the base under the slab. Photo: Sam Galoob

 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

Still reading… Deep Persistent Slabs have been in the forecast every day starting December 14th. Unfortunately it is a concern that we can’t ignore. At high elevations above 3,000’, human triggered large and dangerous deep slab avalanches are still possible. Weak sugary snow (basal facets) near the ground is creating a low probability/high consequence avalanche problem that is impossible to outsmart and will take a long time to heal. A big trigger like a snowmachine, more than one skier on the slope at the same time or a slab avalanche in the upper layers of the snowpack may be enough force to initiate a deep slab avalanche. Likely trigger spots will be in thinner areas of the snowpack that are connected to large, loaded slopes. Cautious route-finding is essential. This includes thinking about the remote trigger potential from below.

 

Weather
Tue, January 9th, 2018

Yesterday was mostly clear and sunny above the valley fog. Temperatures were in the low 20Fs at upper elevations and in the teens to single digits in the valley bottoms. Winds were mostly light and variable.  

Today there will be patchy valley fog in the morning but that should dissipate as cold dry air pushes into the region.  Winds will be northerly 5-15 mph with gusts into the 20s.  Temperatures will be in the low 20s and high teens today, dropping into the low teens and single digits tonight.  

Tomorrow will be partly cloudy with a chance of snow showers in the afternoon and temperatures in the high teens and low 20Fs. Winds will be from the SE 10-20mph. The weather looks to be unsettled into the weekend with snow showers and warming temperatures. Stay tuned!  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 24   0   0   43  
Summit Lake (1400′)  6 0   0    15
Alyeska Mid (1700′)  18 0   0  36

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   variable    4 15  
Seattle Ridge (2400′)  21 S    10  23
Observations
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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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