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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, February 28th, 2016 - 7:00AM
Expires
Mon, February 29th, 2016 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger for Alpine and Treeline (above 1000′) has increased to HIGH again due to heavy precipitation and an unstable wet snowpack. Large natural wet avalanches and glide avalanches are likely today. Travel in avalanche terrain is not recommended until the snowpack has had time to drain. Avoid slopes 30 degrees and steeper, including runout areas in the flats.

The danger is  MODERATE  below 1,000′ where debris from an avalanche above could run in steep terrain.

Elevated caution and a conservative mindset is recomended in the the Summit Lake area where a variety of avalanche concerns exist. See Saturday’s  Summit Lake Summary  and click HERE for recent observations.

Special Announcements

Our deepest condolences to family and friends of a snowmachiner killed yesterday in an avalanche in the Nelchina area. Details of the incident are limited at this time and we will keep you posted as new information becomes available. Click HERE for an article by Alaska Dispatch News and HERE for a report from KTUU.

Sun, February 28th, 2016
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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

Warm temperatures and heavy rain is weaken the snowpack in the mid elevation band. In the last 24 hours 1.8” of water (rain) fell below 1600’ and today another 1” of water is expected to fall by mid-day. This amount of water in the snowpack is increasing the likelihood for large natural wet slabs and wet loose avalanches. This is the type of snow that if a human triggers a wet avalanche it can be impossible to escape from. Our observations yesterday (video below) shows how unsupportable the mid-elevation snowpack was before the additional rain overnight and today. The only way to manage this avalanche problem is by avoiding avalanche terrain all together. Stay off of slopes steeper than 30 degrees, and maintain a safe distance from all run-out zones.

Yesterday several new piles of wet debris were seen from the road along the East face of Seattle Ridge including this wet slab seen near Ingram Creek from the Seward Hwy. 

 

Avalanche Problem 2
  • 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

Today expect strong Easterly winds and an additional 12-15″ of new snow above 1900’. This is on top of a 7-day stretch of very precipitous stormy weather that has produced and estimated 12’ of snow in the alpine and several days of above freezing temperature along Turnagain Pass road (1000′). In the upper elevations natural cornice fall and wind slab activity are likely. These dry avalanches from above could easily run into the mid elevations and entrain wet snow to the valley floor.  Again this is another reason not to go into avalanche terrain today. 

Additional Concern
  • 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

Rain will continue to weaken the snowpack where existing glide cracks litter the mid elevation zones. Over the last two days a handful of glide avalanches have occurred in steep terrain and it is likely more will release today. Glides threaten a lot of well-travelled terrain on both the motorized and non-motorized side of the highway. This concern is listed in the ‘Additional’, but is side by side with all of the above avalanche problems for today. Today is not a good day to play in the mountains. 

Recent glide release on the N side of Eddies, seen from the Seward Hwy yesterday. Click HERE to see more glide observations from the last three days.

Weather
Sun, February 28th, 2016

Overnight 1.8 € of water fell at Center Ridge weather station (1800′) where temperatures remained just cool enough for snow (~18 €.) Easterly winds averaged in the 30’s mph with a gust to 73 mph on Sunburst. Overnight temperatures cooled briefly along Turnagain Pass (1000′) for a short period of wet snow, but temps have already increased to 34F this morning.

Today 1 € of water is expected to fall in the form of rain below 1600′ and 12 € of new snow in the alpine. Warm temperatures could push rain/snow line as high as 1900′. Strong NE winds 30-40mph hour are anticipated along ridgetops. Intensity is expected to lessen by late afternoon, early evening.

Tomorrow showery conditions will persist in the form of rain and snow with the first hope of a break in precipitation Monday evening.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32   18   1.8   156  
Summit Lake (1400′) 34   0   0.3   41  
Alyeska Mid (1700′) 33   3   0.68   106  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25   ENE   31   73  
Seattle Ridge (2400′) 27   n/a   n/a     n/a    
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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.