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Sat, April 18th, 2015 - 7:00AM
Sun, April 19th, 2015 - 7:00AM
Wendy Wagner
Avalanche risk The Bottom Line

There is a HIGH avalanche danger in the backcountry where heavy snowfall, rain and gale force winds are rapidly loading an already unstable snowpack. Large avalanches are likely to occur naturally and human triggered avalanches are very likely on all aspects and at elevations above 1,000′. These slides can be up to 5′ deep, or more, and could propagate across entire slopes; nothing to mess with.

*Hiking trails with avalanche paths above, such as the Crow Pass and Portage Valley areas, should be avoided as debris can funnel into snow free zones and cover portions of trail.

Today’s message is simple:  Travel in avalanche terrain is not recommended, period.  This includes runout zones and valley bottoms where debris from an avalanche releasing above can run. It’s a good day to curl up and watch a movie or finally finish your taxes if you filed an extension…

Sat, April 18th, 2015
Above 2,500'
4 - High
Avalanche risk
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. 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
  • 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

It was an exciting day in the mountians yesterday with a very touchy snowpack in the elevation band between 2,000 and 3,000′. There were three known large avalanches that occurred (3-5′ deep). Two were triggered at the same time, but on different aspects, from the corniced ridgeline on Tincan (CFR ridge) and one was a natural avalanche on Magnum’s North face near Taylor Pass. You can see many great photos and some write ups on our observation page HERE.

Deep Persistent Slabs:
The primary concern for today are naturally occurring deep slab avalanches that fail in lower layers of the snowpack. These can be up to 5′ thick or more and propagate across entire slopes and terrain features. With a foot of new snow and strong wind overnight adding load to an already unstable snowpack, it’s a simple equation to stay away from avalanche terrain. 

There is a mixed bag of weak layers, crusts and interfaces buried anywhere from 2-4+’ deep in our current snowpack. We are unsure what layer was responsible for yesterday’s slides, but the take home point is: There are weak layers/interfaces that have been slowly loaded during the past 2 weeks of storms which are, clearly, still showing signs of reactivity. 

Photos below are of the large slab avalanche on Tincan’s CFR bowl, Southwest facing (left photo: Adam Phillips, right photo: Barkley Blair).



Images below are of the skier triggered slides off both the North and South side of Tincan’s CFR ridgeline. To have deep slab avalanches release on two opposite aspects is very unusual and speaks to our currently very complicated snowpack.

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

Storm snow avalanches associated with just the new snow will be likely but not as large as the deep slab issue mentioned above. Today we can expect wind slabs and storm slabs 1-3′ thick, depending on how much new snow falls. Sluffs should also be expected and could trigger a slab lower on the slope. Cornices will continue to grow and have the ability to fall and trigger large avalanches as well.

Wet Snow Avalanches:
We can also expect wet slab avalanches in the lower elevation band between 1,500′ and 2,500′ due to rising temperatures and a rising rain/snow line today and this afternoon.

Sat, April 18th, 2015

Partly cloudy skies yesterday morning quickly gave way to wind and light snowfall by the early afternoon. Heavy snow began falling overnight along with strong Easterly ridgetop winds. There has been around a foot of new snow at Turnagain Pass and Girdwood Valley with a rain/snow line ~500. Winds have been wreaking havoc at hourly averages in the 60’s and gusts to 107mph. See the charts below for additional 24-hour data.

Today we can expect a short break in precipitation before another 10-14″ of new snow is forecast to fall later today (~1″ water equivalent) with a rain/snow line rising to possibly 1,500′, and even higher. The gale force ridgetop winds are expected to continue from the East, averaging in the 50-60mph range. Temperatures look to rise to the upper 20’s and possibly 30F on the ridgelines and the upper 30’s at 1.000′.

The pulse of precipitation that moves in later today should remain through tomorrow with periods of heavy snowfall and rain to 1,500′. Monday we could see a break in weather before another round of rain, snow and wind early this coming week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   11   1.1   84  
Summit Lake (1400′) 35   2   0.2   14  
Alyeska Mid (1700′) 32   12 0.95   50  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22   ENE    38   107  
Seattle Ridge (2400′) 25   n/a    40 n/a  
Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
11/14/23 Turnagain Observation: Sunburst/Magnum
11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 Turnagain Observation: Tincan Trees
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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.