Turnagain Pass Avalanche Forecast RSS

Archives
ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 31st, 2015 - 7:00AM
Expires
Fri, January 1st, 2016 - 7:00AM
Forecaster
Heather Thamm
The Bottom Line

Multiple avalanche problems exist in the snowpack at different elevations bands today.

A CONSIDERABLE avalanche danger exists both at Treeline and in the Alpine where windslabs 1-4′ will be likely triggered on steep wind loaded features. Today natural activity is not expected in Turnagain Pass, however due to continued stormy conditions and recent rapid loading triggering a deeper more dangerous avalanche will have very high consequences. Therefore today’s travel advice in the Alpine will adhere to the HIGH danger rating where travel is not recommended.

A MODERATE avalanche danger exists below 1500′ where the snowpack is wet and saturated and a larger avalanche from above could easily run into this elevation band.  

*In the Girdwood Valley where more precipitation was recorded overnight natural activity in this area is more likely. Should winds increase beyond the forecasted 20-30mph range today, avalanche danger will be HIGH in the Alpine.

Thanks to our sponsors!
Thu, December 31st, 2015
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
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.
More info at Avalanche.org

Stormy weather has been the theme of our holiday break with over 4.5’ of new snow recorded at Center Ridge Weather Station. On December 29th and December 30th two separate storms brought a mix of rain and snow and high sustained ridgetop winds averaging over 70mph with gusts well over 100mph for multiple hours. Rain/snow line pushed as high as 1800’ saturating the snowpack at the Treeline elevation band. As observed yesterday this rapid loading event has created a variety of avalanche problems that will be challenging to manage today.

1) Wind slab: Triggering a wind slab 1-4’ is likely on steep wind loaded features where multiple layers of wind affected snow exist. Yesterday these wind loaded areas were easy to spot due to their pillow-like shape, but today another 4-5” of snow is expected and moderate Easterly winds 20-30 mph will be transporting more new snow on top, thus adding additional stress to an already stressed out snowpack.

2) Persistent slab: If slides break into older weak layers, we could see very large avalanches, up to 6′ thick (more on this below).

3) Cornices: With such strong winds and warm snow at ridgetops, we can expect cornices to be tender. These ‘backcountry bombs’ are likely to trigger a wind slab or step down to a deeper instability. Avoid ridgelines with large cornices and don’t put yourself below one.

4) Wet loose avalanches: Rain on snow has saturated to upper layers of the snowpack below 1500’. This is more of a concern in areas with terrain traps and in steep channeled terrain where an avalanche from above will be impossible to escape. 

 

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

On the Southern side of Turnagain Pass and extending into the periphery of zone of Summit Lake, this concern is elevated, where a generally thinner snow pack exists. Triggering an older weak layer will be more likely in these areas and possible in Turnagain Pass and Girdwood.  

Some of the avalanches triggered by avalanche hazard reduction by the Alaska Railroad and ADOT ran on older layers, and several large natural D3 avalanche were reported over the last two days including one on Butch Peak in Summit Lake and another at Lower Russian Lake, outside of the forecast zone.

A lot of uncertainty exists as to how easily a person could trigger one of these deeper instabilities. Recent high winds have moved a lot of snow around creating more potential for thinner areas in the snowpack and more stress on the thicker areas. These thin spots will be likely trigger points where a person could unknowingly collapse a weak layer below.  Also a larger trigger like a snowmachine or a cornice failure could be just enough force to tip the balance in deeper areas of the snowpack. Obvious signs of instability like ‘Woomphing’ are unlikely to be present or serve as a warning.

Right now the snow pack is stressed out! It is not the time to get into steep terrain even if a brief window of visibility opens up. The only way to manage this avalanche problem is to avoid steep terrain including being in the runout zone of a steeper slope above. Should you choose to venture into the higher elevation band today cautious routefinding and conservative decision-making are essential. 

This avalanche came down on December 28th and picture was sent to us from the public yesterday. Heads up if you are travelling to Barber Cabin. This is the second time this path has slid in the last month.

Weather
Thu, December 31st, 2015

The last five days has brought 5.4 € ­ ­ ­ ­of snow water equivalent to Center Ridge Weather Station. This has been in the form of mostly snow, but warm temperatures above freezing level reached just above this elevation band on several occasion in the last 3 days. Strong storm force winds averaged in the 70’s mph with multiple gusts reaching 117mph early morning on December 30th. Rain/snow line reached just over 1800′.

Yesterday a brief break in the weather was observed in Turnagain Pass; skies cleared temporarily allowing for a period of cooling on the snow surface. Below 1000′ temperatures stayed above freezing and scattered rain showers persisted all day in Girdwood and Portage Valley. Ridgetop winds decreased into the 20 mph range between 11am €“ midnight.

Overnight showery conditions persisted thoughout the whole forecast zone. Easterly ridgetop winds increased into the 30-40 mph. Rain/snow line remained around 1500′.

Today scattered showers will continue with up to another .5 € of water expected today. This will be in the form of rain below 1500′ and up to 5 inches of snow in the upper elevations. Winds are expected to be moderate from the East, 20-30mph at ridgetops. Expect more scattered showers and above freezing temperatures into the weekend.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32F   4   .8   73  
Summit Lake (1400′) 34F    1 .3   19  
Alyeska Mid (1700′) 33F   3   1.66   53  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25F   ENE   32   72  
Seattle Ridge (2400′) 28F   n/a    n/a   n/a    
Observations
Recent Observations for Turnagain Pass
Date Region Location
12/06/19 Turnagain Avalanche: Sunburst
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
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