Turnagain Pass RSS

ARCHIVED - Forecasts expire after 24 hours.
Mon, December 25th, 2017 - 7:00AM
Tue, December 26th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

There is a  MODERATE  avalanche danger today in the alpine and treeline elevation bands where triggering a hard wind slab will be possible on steep, unsupported slopes.  Above 3,000′ triggering a much larger and more dangerous avalanche is also possible given the poor structure that we know exists high in the alpine.  Obvious clues like €˜whumpfing’ and shooting cracks may not be present until its too late. Evaluate snow and terrain carefully and steer clear of large loaded slopes that have no evidence of past avalanche activity (old piles of debris.)  

There is no hazard rating below 1,000′ due to a lack of snow.  

**Click  HERE  for the Summit Lake Summary posted Saturday.

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Mon, December 25th, 2017
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

Strong Easterly winds have been changing the surface conditions of our forecast zone over the last 4 days creating hard wind slabs on leeward features. Many ridgelines have been exposed down to rocks, dirt and old crusts. Observations yesterday found hard supportable wind slabs as low as 1600’ on Eddies. These slabs averaged around 5” thick and were failing in hand pits on old weak snow. Any wind slabs today will be hard and supportable (to a skiers weight) and may lure a skier well onto a slope before it fails. Be suspect of unsupported slopes steeper than 30 degrees that have a fat, smooth, pillow-type shape to them. Listen for that hollow, drum-like sound below your skis or use a pole to probe for that hard snow over weak set up.  These slabs could be as thick as 1-2’ deep in upper elevations and have the potential for initiating a much larger and more dangerous deep slab avalanche. More on this below. 


A handpit that failed on isolation on weak snow below, near surface facets and buried surface hoar. Yesterday at Eddies at 1900′ on a West aspect. 



Many windward slopes have eroded down to rocks, dirt, and crusts, but cross loading is still possible around gullies and terrain features on windward slopes. Photo of the SE face of Seattle Rigdge near Pyramid Peak. 


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

The recipe for deep slab avalanches has been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facetsObservations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart.



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

  • Large snow covered slopes that do not have piles of old debris under them are all suspect 
  • Thinner areas of the snowpack (1-2’ 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 
  • Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
  • Thicker areas (3-5+’ thick) will be difficult to trigger and several tracks may be on a slope before someone finds a trigger point


This Deep Slab avalanche on the NW face of Pastoral was remotely triggered from below on Dec.20 by a party of two skiers who were able to run out of the way of the debris. This is an example of the potential that still lingers in upper elevations, above 3000′ on slopes that haven’t avalanched. For more details on the snowpack structure click HERE and for a description of what happened click HERE

Mon, December 25th, 2017

Yesterday Strong Easterly winds decreased to Moderate, averaging 15mph with gusts in the 30’s. Temperatures at lower elevations were above freezing, mid to low 30F’s at 1000′ and low 40F’s at sea level. Temperatures at ridge tops remained in the low 20F’s. An inch of new snow fell yesterday.  

Today a trace of snow is possible and winds are expected to be East, 5-20mph.   Skies could range from overcast to partly sunny. Temperatures in the lower elevations should start cooling into the 20F’s today.  

High pressure is expected to settle over mainland Alaska this week with several lows tracking South of the Gulf of Alaska. This should allow for some clear skies and cooler temperatures. Northerly gap winds are possible this week as well as an occasional snow shower.  

*Center Ridge SNOTEL is reporting erroneous temperature data. See  Turnagain Pass DOT weather station  for accurate temperature at 1000′

**A max gust of 72mph occured at 7am on 12/24/17 at Sunburst Wx Staion before winds decreased and gusts were averaging in the 30’s mph most of the day.  
PRECIPITATION 24-hour data (6am – 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) *34   1   0.1   30  
Summit Lake (1400′) 31   1   0.1   11
Alyeska Mid (1700′) 31   2   0.2  27  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   ENE   15   **72  
Seattle Ridge (2400′) 26   ESE   15   48  
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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.