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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, January 1st, 2018 - 7:00AM
Expires
Tue, January 2nd, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is HIGH today at all elevations above 1,000′. Another round of strong wind and heavy snowfall will continue to overload a weak snowpack. Natural avalanches are likely today and tonight. Human triggered avalanches are very likely. As the new snow piles up on a weak layer of buried surface hoar and facets, avalanches are becoming larger and more dangerous. Travel in avalanche terrain is NOT recommended.  

The avalanche danger is  CONSIDERABLE  below  1,000′ where debris from avalanches above may run.

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Mon, January 1st, 2018
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

Yesterday’s NYE storm (New Year’s Eve) greeted many snow enthusiasts with joy. Storm totals were 12-20″ at the mid and upper elevations from Girdwood Valley to Turnagain Pass. On the South side of Turnagain Pass, such as Sunburst and Johnson Pass, only 3-4″ of snow fell… Snowfall amounts were very different from one ridge to the other with this storm. The part of the puzzle that is not joyful however, is a layer of surface hoar underneath the new snow. This has created poor bonding between the new and old snow; proved yesterday by the plethora of human triggered avalanches. To make matters a bit worse, under the surface hoar are near surface facets (another weak layer) and then a hard layer of crust or wind packed snow that is acting as a bed surface. All these ingredients point to likely human triggered avalanches. 

There is another storm headed in today. An additional 5-10″ of snow is expected with another 6-12″ tonight above 1,000′; rain/snow line should be around 500-700’. This will increase the load on the weak layers as well as the slab thickness to over a foot and up to 3′ in places. The storm is coming in warmer and windier, which will also contribute to the increasing avalanche danger. Even small(ish) slopes could become hazardous if the slab is 3 feet thick instead of 1 foot. Keep this in mind if you are headed to the backcounty this week. Also, keep in mind remote triggering is possible from the side or below a slope. Steering well clear of runout zones will be key.

Yesterday’s avalanche activity:
Human triggered avalanches were widespread in the Tincan Trees yesterday. All avalanches were soft slabs or wind slabs around 1-2′ thick and failing on the buried surface hoar mentioned above. Photo below and comment from a group that triggered a larger avalanche in the Tincan Trees (16″ deep, 150 wide and running 200′ ). Triggered remotely by 3rd skier on adjacent slope – no one caught.

“We were pretty surprised at how much energy and how far it ran through trees.”   (Photo Ray Koleser)

Photos of skier triggered soft slabs in the Tincan Trees yesterday. Smaller terrain, smaller slab, smaller avalanches.  (Photos by Trip Kinney) 

  

 

Shooting cracks

 

 

 

 

A look at the new snow sitting on weak layers with a harder wind packed surface below. All known avalanche activity seen yesterday on Tincan was due to the buried surface hoar.

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

In the alpine, above 3,000’, rapidly loading slopes may awaken a large and dangerous deep slab avalanche. At these elevations, a hard slab, 3-5+ feet thick, is sitting on top of weak sugary snow (basal facets) near the ground. As new snow increases the load over this snowpack structure during the current storms, there will be the potential for large natural avalanches. Between storms, human triggered deep slab avalanches will be possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind as breaks between storms may allow for travel to the Alpine. 

Weather
Mon, January 1st, 2018

Yesterday was a classic storm day on Turnagain Pass. Very low visibility, gusts winds and snowfall. Roughly 12 – 20″ of new snow has fallen in the upper elevations of Girdwood Valley and the Turnagain Pass area. 24-hour totals are below in the table. Lesser snow amounts were seen on the South end of Turnagain Pass and in the Summit Lake area. Ridgetop winds were Easterly averaging 25-45mph with gusts to 80mph. Temperatures were in the mid 20’sF at treeline and around 30F at 1,000′.  

Today, New Year’s Day, into Tuesday we have another storm moving in. This one will be warmer, windier and possibly wetter. The rain/snow line looks to rise to around 500-1,000′ before lowering with cooler temperatures tomorrow. Snowfall amounts look to be 5-10″ (.8″ water) of heavier snow today with another 6-12″ (.9″ water) tonight. Ridgetop winds will be Easterly in the 30-50mph range with stronger gusts. Temperatures continue to climb to the mid 30’sF at 1,000′ and upper 20’sF on the ridgetops.

On Tuesday the storm begins to move out and cooler temperatures move in. A break in storms is looking to be Wednesday and Thursday before another low-pressure heads our way.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   8   0.6   40  
Summit Lake (1400′) 30   2   0.2   12  
Alyeska Mid (1700′) 29   10   0.75   39  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20   NE   37   80  
Seattle Ridge (2400′)  24      SE     20   51  
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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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