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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sat, April 9th, 2016 - 7:00AM
Expires
Sun, April 10th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger is  CONSIDERABLE  in Turnagain Pass due to rain, blowing snow and glide avalanches. Below 2500′ large destructive glide avalanches and human triggered wet loose avalanches are possible today. In the Alpine fresh wind slabs, 1′-2′ thick are possible where the snow is drier and winds are strong. Cautious route-finding and snowpack evaluation will be essential, and it will be extra important to avoid being under the runout of glide cracks.

Today’s avalanche problems are in order of encountering them while ascending in elevation and today’s storm should warrant extra caution as the danger increase throughout the day.  If more precipitation falls than expected and winds remain strong, today’s avalanche danger could increase to  HIGH.  Be on the lookout for Natural avalanche activity and adapt to changing conditions.

Summer use trails with avalanche terrain above should be avoided due to natural avalanche activity from above. Byron trail in Portage Valley is not a recommended and the Turnagain Arm Trail between Bird and Girdwood, remains CLOSED.

*If you are headed to the Summit Lake area don’t forget to check  Summit Lake Summary.  

Special Announcements

The Chugach National Forest will be closing some riding areas to motorized use today due to snow melting out.  Please see the table at the bottom of this page for a complete list.  Snug Harbor, Summit Lake and Turnagain Pass (N. of Granite creek) will remain open.  

Sat, April 9th, 2016
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

The possibility of wet loose avalanche activity will increase throughout the day with rain saturating the snowpack in the Treeline zone. Rain (~0.76″) is expected up to 2000’ and could weaken the superficial surface crust. If the snow becomes unsupportable and your skis/snowmachine start sinking into punchy wet snow, this is an obvious sign the snow is loosing its strength. In the mid elevation where wet snow is falling on a slick bed surface, triggering a wet loose avalanche could be especially dangerous at the bottom of a terrain trap or on a large slope. Monitor the depth of this wet heavy snow, and stay off of slopes steeper than 35 degrees if the snow is wet and saturated.

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks continue to be actively releasing in popular terrain. On April 7th between 4:51pm and 5:07pm, Turnagain DOT web camera (currently not available online) photographed a very large glide above part of the uptrack. The debris covered many recent snow machine tracks traversing to & from the uptrack as well as recent high marks in this area. The good news is nothing bad happened, and no one was caught during a sunny afternoon at a popular time of day. The bad news is there are more cracks in this area that still threaten the uptrack.

Today increasing avalanche danger and poor visibility will make the decision ‘not to go’ into this area easier. Also be aware that rain and wet snow will be adding stress to glides today and we may see a spike in glide releases again over the next few days. Remember avoidance is key; if you were to be in the wrong place at the wrong time getting caught up in a glide avalanche would be unsurvivable. 

Repeat Offender near the Seattle Ridge Uptrack. Photo taken at 10:30am on 4/9. 

Additional Concern
  • 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

Yesterday blowing snow was observed in the alpine as Easterly winds started building from the East. These winds increased overnight averaging in the 30-40’s mph with gusts in the 60’s mph. Around three inches of new snow fell overnight and another 5-10” is expected above 2000’. Fresh and tender winds slabs will be forming on a slick bed surface and could be a thick as 1’-2’ deep on leeward terrain features and along ridges and gullies. Small test slopes and hand pits will be good ways to test the snow as you gain elevation. Monitor snow depths and look for any signs of unstable snow like shooting cracks or recent avalanches. Today it will be important to stick to mellow terrain by keeping slope angles below 35 degrees.

Cornices: Blowing snow will be adding stress to cornices today and natural activity is possible. Some cornices are gigantic this winter and skier or snowmachiner could be the tipping point should someone get too close.  Remember they have a tendency to break much further back than one might expect. Give them extra space and avoid travel directly below cornices. 

Yesterday an observer in the Taylor Pass/Pastoral area experienced building winds and blowing snow starting around 2pm yesterday.  Photo by Liz Repetto.

Weather
Sat, April 9th, 2016

Yesterday skies were clear in the morning becoming cloudy in the afternoon. Ridgetop winds started building mid day becoming strong by early evening, averaging in the 30-40’s mph overnight. Yesterday temperatures reached the mid 40F’s at 1000′. Overnight temperatures at Center Ridge Weather Station remained above freezing with a low of 32F at 1am. 1 € of new snow was recorded and .2 € of water.

An approaching front is bringing widespread showers and strong winds to Southcentral Alakska. Today 0.76 € of water is expected in the form of rain below 2000′, and 5-10 € of new snow could fall in the upper elevations. Strong Easterly winds will persist into the early afternoon becoming Moderate by early evening. Daytime temperatures at 1000′ are expected to reach the low 40F’s and remain above freezing overnight.  

Overnight and into tomorrow an additional 0.9 € of water is expected and winds will remain Moderate from the East. Temperatures may start to cool slightly, with rain/snow line ~1500′.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37   1   0.2   115  
Summit Lake (1400′) 39   0   0   34  
Alyeska Mid (1700′) 36   1   .39   102  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   NE   20 75  
Seattle Ridge (2400′) 30    SE 21    58
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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.