Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 29th, 2017 - 7:00AM
Expires
Sat, December 30th, 2017 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

There is a  MODERATE  avalanche danger today in the alpine, above 3,000′ where triggering a large and dangerous deep slab avalanche is possible due to weak snow near the ground. Triggering an isolated hard wind slab is still possible on steep leeward features or on unsupported terrain in the alpine.  Heightened avalanche conditions exist on specific terrain features. Evaluate snow and terrain carefully.

 

The avalanche danger is LOW at Treeline. LOW danger does not mean NO danger. Pockets of unstable snow are not out of the question if you find yourself in very steep terrain, below 2500′. There is no hazard rating below 1,000′ due to a lack of snow.  

*Please remember your safe travel practices! This includes, exposing one person at a time in avalanche terrain, watching your partners, being rescue ready and having an escape route planned.

**Click HERE for several new observations from Summit Lake.

Thanks to our sponsors!
Fri, December 29th, 2017
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • 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

It has been over a week since a large avalanche was triggered on Pastoral by two skiers traveling below the NW face. If you have been reading the forecast regularly we are not trying sound like a broken record but the message is the same. This snow pack set-up continues to warrant elevated caution and respect. It is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. The ingredients for a deep slab avalanche have been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche in the early December storm cycle. This is a hard slab, 3-5+ feet thick, sitting on top of weak sugary snow (basal facets) near the ground. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations.

 

When dealing with a deep slab avalanche problem, keep in mind:

  • Large snow covered slopes that do not have large piles of old debris under them are all suspect 
  • Thinner areas of the snowpack (1-2 feet thick) are likely trigger spots as well as scoured areas near rocks   
  • It is possible to trigger this avalanche from below and it could run further than expected 
  • Snow depths are highly variable and there may be more trigger spots than we realize
  • Several tracks on a slope do not mean the conditions are safe. It could be the 2nd, 3rd or 10th person on a slope before someone finds a trigger spot.

 

Weak faceted snow near the ground continues to be reactive and signal propagation potential in test pits in the alpine. Check out a video HERE and observation from Magnum on 12/27/17 HERE

 

Over the last two weeks we have been trying to inventory terrain that has or has not avalanched like this observation sent yesterday from Seattle Creek. Photo taken and annotated by Peter Wadsworth. Check out his observation HERE.

Avalanche Problem 2
  • 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

Cold temperatures and stable weather this week have been making the snow more brittle and faceting out surfaces. With that said triggering an old wind slab is still possible on very steep terrain in the alpine zone. Places you might find a hard wind slab will be in steep couloirs, large unsupported terrain features, or in thin rocky areas. Triggering a wind slab in the Treeline zone is becoming less likely, but is not out of the question in high consequence terrain. This also goes for a few inches of fast moving loose surface snow “sluff” that could catch you by surprise if you’re not expecting it. Triggering a wind slab could take you for an undesirable ride, and has the potential for initiating a much larger and more dangerous avalanche above 3000′. Be suspect of any slopes that may harbor a deep slab problem in the upper elevations as described above. 

Thin wind slab crowns from a wind event that ended Dec.24 were seen on North and West aspects in Seattle Creek yesterday, as well loose surface snow. Photo by Peter Wadsworth. 

Weather
Fri, December 29th, 2017

Yesterday skies were mostly clear and temperatures along ridgetops averaged in the teens (F) with pockets of colder air at valley bottoms. Valley fog was present along Turnagain Arm. Winds were light and variable and no precipitation was recorded. Overnight thin cloud cover has moved into the region

Today skies are expected to be overcast with light Easterly winds. Temperatures should remain in the mid teens (F) to low 20F’s along ridgetops. Snow flurries are possible, but only a trace of snow is expected.  

A big pattern change is on tap for this weekend. Snow should start falling on Saturday with the intensity picking up late Saturday evening into Sunday morning. Several feet of snow is possible for the Kenai Mountains.   Strong Easterly winds are expected as well as rapidly rising temperatures which could change snow to rain at lower to mid elevations as the storm progresses.  

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 20   0   0   30  
Summit Lake (1400′) 8   0   0 12  
Alyeska Mid (1700′) 17   0   0   26  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13   W 2   11  
Seattle Ridge (2400′) 17   variable     3   14  
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/04/19 Turnagain Observation: Sunburst
12/03/19 Turnagain Observation: HIppy Bowl
12/01/19 Turnagain Observation: Tincan, All elevations
12/01/19 Turnagain Observation: Tincan
11/30/19 Turnagain Observation: Tincan Treeline Plateau/ Common Bowl/ Ridge
11/29/19 Turnagain Observation: Sunburst Ob #2
11/29/19 Turnagain Observation: Sunburst Ob #1
11/27/19 Turnagain Observation: Tincan
11/25/19 Turnagain Observation: Sunnyside
11/18/19 Turnagain Observation: Turnagain Pass – Road obs
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.

Subscribe to Turnagain Pass
Avalanche Forecast by Email