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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, January 15th, 2018 - 7:00AM
Expires
Tue, January 16th, 2018 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

A CONSIDERABLE avalanche danger remains at elevations above 1,500′ in the Turnagain Pass area. Triggering a large slab avalanche was likely yesterday and trending toward possible today. However, it is only the 2nd day after a storm and these slabs are 2-5+’ thick and unmanageable. Today is a day to follow the ‘travel advice’ for CONSIDERABLE danger: Careful snowpack evaluation, cautious route-finding and conservative decision making. A LOW avalanche danger exists below 1,500′ where triggering an avalanche is unlikely.

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Mon, January 15th, 2018
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
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
  • 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

Storm slabs, wind slabs and cornice falls associated with the heavy snowfall two days ago are still an issue today. Although the bonding of the new snow to the old snow surface is occurring quickly, slabs and cornices may still be triggered. Yesterday there were three large avalanches seen/reported in the Turnagain Pass zone. Two of these were in Main Bowl of Seattle Creek and were storm slabs triggered by snowmachiners. One was triggered by a cornice fall and one was remotely triggered from above. The third avalanche was on the SE face of Seattle Ridge and is unknown if this was a natural slide or triggered remotely from a snowmachiner(s) on the ridge. An avalanche course heard the slide from across the valley. This third avalanche looks to have stepped down into deeper weak layers in the pack. See photos below.

For today, if visibility allows for travel to the upper elevations, know that these types of avalanches remain possible. Furthermore, cornices have grown and could break farther back than expected. It is only the 2nd day out of a storm and don’t expect all slopes to remain intact. Although triggering a storm slab or wind slab avalanche will be less likely today, these slides can be large and have high consequences. Quick hand pits and getting your shovel out to look at the new/old snow bonding is a good way to help assess the slopes you are interested in riding. Assessing deeper weak layers in the pack is more difficult – more on that below. Keeping with safe travel habits, chiefly exposing only one person at time if venturing into avalanche terrain is key. Watch your buddies closely. 

 


Close up of the crown of avalanche above, note the dark bed surface, this avalanche ‘stepped down’ into weak snow near the ground

 

Yesterday a snowmachine triggered a cornice fall, which triggered this storm slab avalanche in Main Bowl (1st Bowl) in the Seattle Creek drainage. 

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

Triggering a deep persistent slab is just as concerning, if not more concerning, as the avalanche issues in the new snow. This is because these can be larger and more destructive avalanches. Underneath the storm snow sit a variety of weak layers deeper in the snowpack. The first is the New Year’s buried surface hoar that is anywhere from 30″ to ~5′ deep (general snow depths vary widely due to wind distribution and snowfall differences). This layer was showing signs of being reactive in pits yesterday – it took a bit of force to fail, but once it fails, it’s sliding easily. There are also facets that have been found near crusts in the mid to lower pack as well as basal facets that sit near the ground. The point is, this is a complicated snowpack that just received a lot of weight – avalanches triggered deeper in the pack can be very large and unsurvivable.

 

Video of failure in the New Year’s buried surface hoar on Sunburst ridge, while the storm snow has bonded well in this area

Weather
Mon, January 15th, 2018

Partly sunny skies filled the area yesterday with no precipitation. Ridgetop winds bumped up to the 30’s with gusts in the 50’s mph yesterday morning from the East before tapering off significantly in the afternoon and overnight have been light and variable. Temperatures remained warm, in the mid to upper 20’sF along ridgetops and in the mid 30’sF below 1,000′. A slight inversion is in place this morning with valley bottoms in the upper 20’sF.  

Today, we are just on the edge of some instability showers to our Northeast. We may see partly clear skies with no precipitation, yet we may also see these showers back down our way to bring 1-2″ of snow above 1,500 and light rain (.2″) below this. Ridgetop winds are expected to be relatively light, 5-15mph from the East today and into tonight. Temperatures will stay on the warm side with mid 30’sF at 1,000′ and the upper 20’sF along the ridgelines.

Early tomorrow another warm storm system moves in from the East. As of now, the rain/snow line looks to be around 2,000′ and possibly higher. Models are showing precipitation amounts in the 1-2″ of rain and 1-2+ feet of snow up high by Wednesday night. Stay tuned and cross your fingers for a lower rain line.

*A big THANKS to the folks who cleared off the Seattle Ridge weather station yesterday!  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31   0   0   60  
Summit Lake (1400′) 28   0   0   15  
Alyeska Mid (1700′) 33   trace   0.04   48  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 27    NE 21   55  
Seattle Ridge (2400′) 29   SE   15   30  
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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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