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Sun, April 9th, 2017 - 7:00AM
Mon, April 10th, 2017 - 7:00AM
Heather Thamm
Avalanche risk The Bottom Line

The avalanche danger  is CONSIDERABLE  above 1000′ due to weak snow sitting under 2-6+ feet of storm snow in Turnagain Pass, Placer Valley and Girdwood.  Human triggered avalanches 2-6+ feet deep are likely  today  on slopes that haven’t avalanched already. The likelihood of triggering will increase during the heat of the day and natural avalanches will be possible. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential.  

Below 1000′ a MODERATE avalanche danger exists where triggering a wet avalanche will be possible during the heat of the day.  Watch for changing conditions.

Hiking in Portage Valley and on summer trails around the Advisory area (including the Turnagain Arm Trail a.k.a the bike path).  Avalanches occurring at the higher elevations in this last storm sent large amounts of debris into valley bottoms and covered snow-free hiking trails. Continue to avoid trails that cross under avalanche paths such as Byron Glacier or portions of the Trail of Blue Ice and Crow Pass. The Turnagain Arm Trail between Bird and Girdwood remains  CLOSED for the winter.

Summit Lake:  An active avalanche cycle has occurred in Summit Lake this week and ELEVATED  CAUTION is advised.  Read the  Saturday Summit Summary  HERE  and observations from the last few days  HERE.

Special Announcements

Southcentral Alaska has been experiencing a widespread avalanche cycle over the last week due to warm temperatures, snow and rain, and strong winds and now SUN!!! Dangerous avalanche conditions are expected region wide including: Lost Lake, Hatcher Pass, and the Anchorage Front Range. Above freezing day time temperatures are forecasted throughout the weekend and human triggered avalanches will be likely.  

Sun, April 9th, 2017
Above 2,500'
3 - Considerable
Avalanche risk
3 - Considerable
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
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Yesterday we received reports of three seperate human triggered avalanches in Seattle Creek Zone, and possibly a fourth. These were large slab avalanches that likely failed on the March 28th buried surface hoar and/or the March facets. Incident details are unclear, but so far there have been no reports of anyone buried or injured. These were not small avalanches – they were all 3-6+ feet deep, maybe larger and propagated long distances. Bottom line an avalanche this size could be unsurvivable. There was also a very large Natural avalanche in Portage Valley yesterday. The Portage DOT web cam captured the debris in motion at the bottom of the avalanche path at 5:10pm.   

Test pits yesterday found easy propagation potential in reactive buried surface hoar on Sunburst. (See video below.) A 10-day storm cycle that ended Friday morning has left anywhere from 3 feet to 6+ feet (possible more in Portage/Placer/20 mile area) of snow in the upper elevations. Strong storm winds also created variable slab depths. This storm cycle came as rain in the lower elevations and produced a widespread large natural avalanches region wide. Slopes that didn’t slide during the storm are suspect. Slabs maybe slightly harder to trigger and it may not be the first person on the slope. Spring time conditions and daily warming in the afternoon will increase the likelihood of triggering.  Ease into terrain and avoid terrain traps. Follow safe travel protocols and pay attention to other parties in the area. Conservative decision-making is essential. Don’t let the sunny weekend lure you into an accident. Be patient! 

Human triggered slab avalanche in 1st Bowl (aka Main Bowl) that occured yesterday (4/8/17.)  If anyone has more details or pictures of any of the Seattle Creek avalanches yesterday please submit an observation HERE. It’s easy and can be done anonymously. Reporting near misses can help prevent future accidents and save lives!!! 



This natural avalanche happened yesterday in Portage Valley and ‘debris in motion’ was capture on the Portage DOT web cam.  



Avalanche Problem 2
  • 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

Widespread wet avalanches have occurred this week due above freezing temperatures and rain below 2700’. Yesterday there was a very large sun-triggered avalanche in Portage Valley and widespread roller ball activity and some wet loose avalanches on Southerly slopes. Mostly clear skies overnight and temperatures below freezing have created a solid crust in the lower elevation band. A sun crust also extends into the Alpine on solar aspects. Yesterday’s warm temperatures caused these crusts on steep Southerly aspects (both in the lower and upper elevations) to completely break down causing the snowpack to be wet and saturated. In the morning with freezing temperatures, the snowpack will be more stable, but as this crust starts to degrade, this is when human triggered avalanches will become likely on slopes steeper than 35 degrees. Temperatures are forecasted to rise into the mid 40Fs again today and solar heating is certain, either through thin clouds or direct sun light. In the afternoon, when the crust melts wet-loose avalanches will be possible. This daily warming will also increase the potential for triggering a deeper slab in drier layers in the alpine, on ALL ASPECTS! Pay attention to roller balls indicating surface warming and avoid slopes if you start sinking into wet snow on your skis or snowmachine. 

Wet avalanches that occured on Seattle Ridge during the 10 day storm cycle. Photo taken 4/5/17 


Additional Concern
  • Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Strong winds throughout the storm cycle combined with the heavy snow have created large cornices overhanging leeward slopes. Daily warming is also contributing to their instability. Yesterday there was a possible cornice triggered slab avalanche in Seattle Creek. Details are unconfirmed, but either way avoid travel on or underneath these backcountry bombs. They are likely to trigger a large avalanche on the slope below and often break further back on a ridge than expected.  

Sun, April 9th, 2017

Yesterday was clear and sunny. Daily spring time temperature swings were between mid 20F’s in the morning reaching mid 40F’s by mid to late afternoon at sea level. In the upper elevations Sunburst wx station recorded above freezing temperatures between 1pm and 5pm with a high of 38F. Ridgetop winds were light (5-10mph) from the East and picked up later in the evening to 10-20mph. No precipitation was recorded. Overnight temperatures have dropped below freezing.

Today temperatures are expected to be in a similar range. Temps in the mid 20F’s this morning increasing to high 30F’s to mid 40F’s by the early afternoon. There is a chance for scattered snow/rain flurries today, with a possibility 1 € of snow (0.1 € of water.) Clear skies this morning could range from partly cloudy to cloudy this afternoon. Ridge top winds are expected to be in the 5-15mph from the SE today.

A similar spring time pattern is expected this week. No significant changes are in the immediate forecast. Expect clear skis to partly cloudy through midweek.   Diurnal daily temps swings could range from 25F to mid 40F’s this week.  

*Center Ridge Snotel site and Summit Lake Snotel sites stopped recording data from 9am to 10pm on 4/8/17.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) *n/a   *0   *0 *74
Summit Lake (1400′) *  n/a   *0 *0 *26  
Alyeska Mid (1700′) 35   0   0   68  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 28   E   4   22  
Seattle Ridge (2400′) 28   SE   9   20  
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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.