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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, January 13th, 2018 - 7:00AM
Expires
Sun, January 14th, 2018 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

An avalanche warning has been issued for Turnagain Pass, and the avalanche danger remains HIGH at all elevations due to rain, heavy snow, strong winds and above freezing temperatures.   Natural and human triggered wet slab avalanches and storm slabs 2-4 feet deep will be likely today in avalanche terrain and could run to valley bottoms. Travel is not recommended on or near slopes steeper than 30 degrees including runout zones.  

*Portage and Whittier, outside of our advisory zone, has received double the amount of precipitation as Turnagain Pass and another 2 € of rain is expected today. Avalanche activity in these zones may run to valley bottoms.  

For information about the Summit Lake avalanche conditions click HERE.

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Sat, January 13th, 2018
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
High (4)
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
High (4)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Wet Slab
    Wet Slab
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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

Rain on snow is expected below 1500’ and will be adding significant stress to the snowpack in the mid and lower elevation zones. A weak interface (facets and buried surface hoar sitting on a crust) is underneath yesterday’s 20” of storm snow. Add today’s rain and this is a perfect recipe for wet slabs. Natural and human triggered wet slabs 2-3 feet deep are likely on slopes steeper than 30 degrees including both large and small terrain features. Triggering this kind of avalanche will be impossible to escape and could be unsurvivable. It will be very important to avoid terrain traps and being near the runout of larger slopes. 

 

Remote triggered avalanche on Tincan yesterday. This is a good example of a small terrain feature that could be releasing naturally if rain saturates the snowpack today. Photo credit: Matti Silta

 

Avalanche Problem 2
  • 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 20” of new snow was observed in Turnagain Pass and today another 12-20” of heavy snow is expected in the upper elevations above 1500’. Natural slabs 3-4 feet deep will be likely today and human triggered avalanche very likely. Strong Easterly winds in the 40’s with gusts in 90’s are also anticipated. All 6 Red Flag warning signs were observed yesterday at Turnagain Pass. This includes a remote triggered avalanche on Tincan,  large shooting cracks, collapsing “whumpfing sounds”, rapid loading due to heavy snow and strong winds, and warming temperatures. All of this new snow has fallen on surface hoar and near-surface facets and slabs will be easy to trigger. Below 2000’ these weak layers are sitting on a slick crust  and a slab could easily catch you by surprise, even in the protected trees of Tincan or getting your snowmachine stuck under a small steep terrain feature. Strong winds today could trigger a large natural avalanche that could run down to valley bottoms. Maintaining a safe distance from the runout zones of all larger slide paths including Repeat Offender will be important. Remote triggering an avalanche from below or above is also possible. Basically today is a good day to avoid the mountains around Turnagain Pass. In fact this is a good day to head to Hatcher Pass and practice your avalanche rescue skills. Click HERE for details about the free clinic. 

A very large shooting crack on a wind loaded terrain feature was intentially triggered by a snowmachine near the motorized lot yesterday. Windloading has created variable slab depths. Slabs could be as deep as 4-5′ on leeward features. 

 

Additional Concern
  • 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

Natural and human triggered avalanches today could step down to deeper layers of the snowpack producing a very large avalanche depending on the size of the slope. A layer of buried surface hoar from the New Year’s holiday has been showing propagation potential in test pits including a pit dug yesterday at 2000′ on Tincan by an avalanche course. In addition, a Deep Persistent Slab problem remains a concern in the upper elevations above 3000’, and serves as one of the many reason to avoid avalanche terrain today. 

Weather
Sat, January 13th, 2018

Yesterday Center Ridge Snotel recorded 0.6 € Snow Water Equivalent (SWE) at 1700′ and the RWIS DOT Wx station recorded (1.13 € SWE) at 1000′. Field observations confirmed about 20 € of new snow since Thursday when the storm began.   Sunburst Wx station showed strong Easterly winds all day averaging in the 40’s mph with a gust to 92mph last night. Rain/snow line started out at sea level yesterday morning and increased to just below 1000′ this morning.  

Today there is .95 € rain (SWE) expected, this translates to another 12-20 € of snow in the upper elevations. Unfortunately rain/snow line will continue to rise to 1500′ possibly higher. Strong winds will continue to blow from the East and average in the 40’s mph with gust in the 80-90’s mph. Peak intensity and warmest temperatures should begin later morning through 8pm this evening.

Tomorrow afternoon another front is expected. There’s some uncertainty as to how much precipitation and wind, but temperatures are expected to remain warm.  

*RWIS DOT weather station at 1000′ on Turnagain Pass recorded 1.13 € SWE. This weather station is located further North where precipitation is often heavier than then further South in Turnagain Pass.  

**Seattle Ridge weather station is covered with rime and stopped recording wind data at 4pm yesterday (1/12/18)

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   *4   *0.6   57  
Summit Lake (1400′) 34   1   0.1   15  
Alyeska Mid (1700′) 32   4   0.92   48  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   ENE   42   92  
Seattle Ridge (2400′) 26   **SE   **24   **46  
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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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