Turnagain Pass RSS

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Sat, February 14th, 2015 - 7:00AM
Sun, February 15th, 2015 - 7:00AM
John Fitzgerald
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE today in the Alpine on steep wind loaded slopes.   Freshly formed slabs up to 12 € thick will be easy to trigger and could release naturally.   The danger is MODERATE on non wind loaded slopes in the Alpine and in the Treeline elevations, where pockets of shallow slab ranging from 4-8 € thick could be triggered on steep slopes.   Wet loose avalanches are also an issue to contend with today in the lower elevations where warm temperatures and occasional rain will weaken the snow surface.

Sat, February 14th, 2015
Above 2,500'
3 - Considerable
Avalanche risk
2 - Moderate
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
  • 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

Snow does not like rapid change.  When rapid change occurs, weak layers have a hard time adjusting to the load.  Winds overnight have brought about this rapid change.  Slabs have been actively growing on leeward slopes in the higher elevations.  Winds have been mainly out of the East.  The important thing to remember about wind is that direction changes are common in mountainous terrain.  With that said, recognition of wind loaded slopes is a better assessment tool than reading the weather station data when it comes to wind direction and loading patterns.

Shooting cracks and collapsing are obvious indicators of unstable slabs.  Stiff, hollow and upside snow should be avoided today in leeward starting zones and cross loaded terrain features.  These slabs could build into the 12” range and have enough volume to injure or bury a person.

Avalanche Problem 2
  • 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

A layer of weak faceted snow sits anywhere from 2-16” below the surface.  This layer is widespread throughout the forecast area.  This layer is deepest on the North end of Turnagain Pass (Eddies, Pyramid) where snowfall earlier in the week put down slabs up to 12” thick.  Heading South along the Pass that slab gradually gets thinner and less continuous across slopes with averages in the 6-8” range.  As a result we have seen more reactive snow where that slab is thicker, including remotely triggered avalanches within the last 2 days.  In the Girdwood Valley we have a different setup, where older dense wind slabs 4-8” thick that formed a week ago are sitting on this weak layer and concealed by 6″ of snow that has fallen this week.  

To put it simply, we have the perfect recipe for a slab avalanche in many areas today; slab + weak layer.  Add into the mix the right terrain (slopes 35 degrees and greater) and a trigger (humans or rapid loading of snow) and the result is avalanches.  

Avalanches could occur within newly formed wind slabs and they could also step down to this weak layer.  Regardless of the actual failure layer, it will be important to avoid slopes 35 degrees and over that have this slab/weak layer combo.

Additional Concern
  • 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

A continuation of above freezing temperatures in the mid elevations along with occasional rain will make wet loose avalanches another concern today.  Volume of these will be generally low.  Despite this it will be important to recognize and avoid steep terrain that is holding loose, weak and damp snow.  This snowpack issue becomes more concerning when traveling above terrain traps such as cliffs, gullies and trees.

Sat, February 14th, 2015

The greatest change in the past 24 hours is in the wind category.   Ridgetop winds picked up overnight with the Sunburst weather station averaging in the 20-30 mph range since 10 pm.   Light rain and snow have been falling with the rain/snow line fluctuating between 1,500 – 2,000′.   Temperatures as you might guess have been warm with ridgetops in the low 30s F.

Today expect snow and rain showers throughout the day.   Rain/snow line should hover around the 1,500′ mark.   Snowfall amounts will be in the 2-3 € range above this line.   Winds will be out of the East at 15-20 mph with higher gusts.   Temperatures will remain mild with ridgetops in the low 30s F.

The extended outlook shows a continuation of warm temperatures and precipitation.   Sunday night into Monday looks to bring the next round of more significant moisture and warm temperatures to the area.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 1 .1 36
Summit Lake (1400′) 28 0 0 9
Alyeska Mid (1700′) 31 Trace .1 26

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 30 E 15 46
Seattle Ridge (2400′) 30 NE 8 34
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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.