Turnagain Pass RSS

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Wed, April 5th, 2017 - 7:00AM
Thu, April 6th, 2017 - 7:00AM
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

Rising temperatures, additional rain, snow, and wind will keep the avalanche danger at  HIGH  again today  for the Turnagain Pass area and surrounding mountains. Natural avalanches are still likely at all elevations and human triggered avalanches are very likely.  Travel is not recommended in avalanche terrain. If choosing to play in the flats, make sure to steer well clear of gullies and the bottom of steep slopes in the event an avalanche releases above you.

Hiking in Portage Valley:    Avalanches occurring at the higher elevations can send large amounts of debris well into valley bottoms and cover snow-free hiking trails. Avoid trails that cross under avalanche paths.  

Summit Lake:    Travel in avalanche terrain is not recommended.  Read the  Saturday Summit Summary  HERE.

Special Announcements

Roof avalanches have been occurring over the past week in Girdwood due to warm temperatures and rain.  Be aware that roofs will continue to shed today and into this coming week.

Wed, April 5th, 2017
Above 2,500'
4 - High
Avalanche risk
4 - High
Avalanche risk
Below Treeline
Below 1,000'
4 - High
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. Dangerous avalanche conditions. 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

Due to periods of heavy snow, rain and strong winds, yesterday was the most active day for avalanches yet in this series of storms. A majority of the avalanche terrain that was visible below 2500′ had avalanched. Much of the activity observed was wet avalanches at lower elevations. It was hard to get a good look into the Alpine. For today it is important to remember that conditions remain touchy and travel in avalanche terrain is not recommended. Avalanches may also step down into weak older layers in the pack, creating an even larger slide.

Strong winds yesterday combined with heavy snow will have created large wind slabs and cornices on leeward slopes. With temperatures rising to above freezing in the Alpine these may release naturally and could entrain enough snow to run quite far. Any additional wind today will also add stress.

In areas out of the wind, expect the recent storm snow to still be reactive. Human triggered slab avalanches 2-4′ thick are very likely.  

How much load is on the old weak surface from March? Storm totals (March 27 – 6am April 5th):

Turnagain Pass:     4″ of H2O, 45+” of snow at upper elevations
Girdwood Valley:    5″ of H2O,  55+” of snow at upper elevations
Summit Lake:         1.5″ of H2O,  15+” of snow at upper elevations   

 AKRR/DOT Avalanche Hazard Reduction triggered slide in the Centerline path on the Seward Highway yesterday. 

Avalanche on Seattle Ridge across from the Sunburst parking lot.


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

Yesterday periods of heavy rain, rising temperatures and strong winds initiated a widespread wet avalanche cycle below 2500′. The rain/snow line climbed to approximately 1,500′, possibly higher in places.  Many slopes across the advisory area had piles of wet debris at the bottom. Artillery triggered slabs caused long running slides that gouged into wet snow and weak deeper layers in the snowpack. Slopes that did not slide may still today as temperatures climb above freezing in the Alpine and dry snow at upper elevations becomes wet. Additional rain to 2300′ will also add load and contribute to instability. In the event that the sun makes an appearance wet activity may also be exacerbated by more heat.



Avalanches along Seattle Ridge towards the uptrack.


Additional Concern
  • 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

The balance was finally tipped and avalanches yesterday were observed stepping down into old weak layers. Dirty debris in places indicted that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6′ and running the entire length of a slide path.  



Multiple layers of buried surface hoar and facets exist within the snowpack. These layers are overloaded and avalanches are breaking into them.


Wed, April 5th, 2017

Yesterday was cloudy and the ceiling was low for most of the day. Heavy rain and snow fell on and off throughout the day totaling around an inch of water. 6-12″ of snow fell at upper elevations. Rain/snow line was approximately 1500′. Winds were Easterly blowing 20-40 with gusts into the 70s. Temperatures were in the high 30Fs to low 40Fs at sea level, 30s at mid elevations and mid to high 20s at ridgetops. Winds tapered off overnight and temperatures rose slightly.  

Today is a small lull in the system. Temperatures are forecasted to rise with temperatures at 3000′ reaching 36F. The skies will be mostly cloudy with rain/snow showers throughout the day with little to no accumulation expected. Winds will be Easterly 20-30 mph with gusts into the 40s increasing in the afternoon/evening. Precipitation will pick up overnight.  

Tomorrow temperatures are forecasted to cool a little. Snow and rain showers will continue into remainder of the week with a chance for some clearer skies and sun this weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 37   rain .8   85  
Summit Lake (1400′) 36 rain   .2 29  
Alyeska Mid (1700′) 34 rain   .65    74

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  26 ENE    30 71  
Seattle Ridge (2400′)  29 sensor rimed   sensor rimed   sensor rimed  
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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.