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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, December 30th, 2016 - 7:00AM
Expires
Sat, December 31st, 2016 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A CONSIDERABLE avalanche danger exists in the mountians surrounding Turnagain Pass on all slopes out of the trees. Strong winds are expected to form wind slabs that could release naturally and be easy to trigger by a person. Winds could blow below ridgelines and load, or cross-load, slopes that sit near treeline that are exposed to wind.

In sheltered areas a MODERATE danger exists where triggering a slab avalanche 1-2′ thick, that breaks in older snow, remains possible. This was the case yesterday when a human triggered slab avalanche caught and carried three skiers (Please see details in the  ‘Persistent Slab’ section below).

Johnson Pass region: A shallower snowpack exists in the mountains South of Turnagain Pass. We have no information in this area yet – if you are headed this way, a  conservative mindset is recommended along with easing into terrain. Triggering a slab avalanche is possible and could be triggered from below, similar to what occurred to three skiers yesterday.

Safe travel protocol will be essential if you choose to enter avalanche terrain: Expose one person at a time, group up in safe zones, watch your partners and always have an escape route planned.  

Special Announcements

Johnson Pass North and South are open as of 7am this morning to motorized use. Please stay on the designated motorized trail – map HERE. The snowpack is unknown and questionable in this area – please read the following forecast.

*Alaska DOT may not get to clearing the Turnagain Pass motorized lot this weekend. Please park safely and respect plow operations.  

Fri, December 30th, 2016
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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

A quick moving storm is impacting Southcentral currently. We have seen light snowfall overnight with an additional 1-3″ expected today. The big news is however, the WIND… Westerly winds are slated to ramp up into the 30-45mph range with stronger gusts along the ridgelines

Snowfall Totals so far:
Girdwood Valley:  3-5″
Turnagain Pass:   2-3″
Summit Lake:       3-4″

WIND SLAB AVALANCHES:
With plenty of older loose snow available for transport and a few new inches, fresh wind slab avalanches should be expected. These could release naturally, or be easily triggered by a person. They could be anywhere from a shallow 6″ slab to a thicker, more concerning, 18″ slab. This flow direction is known to load Easterly slopes on Seattle Ridge, such as Repeat Offender. On the East side of Turnagain Pass, this flow often loads Northerly slopes on ridgelines such as Tincan, Sunburst and Magnum. 

*Keep in mind that newly wind loaded slopes could overload buried weak layers and a wind slab avalanche could ‘step-down’, triggering a larger slab avalanche. 

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

We are glad to report a positive outcome to a near miss avalanche yesterday on the Lipps ridge. Three skiers were caught and carried in a slab avalanche while they were ascending the common up-track on the lower portion of Lipps. The avalanche was triggered in a thin area and propagated above them. The slab washed over all three and they were carried 1-200′ (estimate) before they all ended up on the surface of the debris. Forecasters will investigate this avalanche today and a more detailed report, with the events shared by the party members along with avalanche details, will be finalized soon. You can see more photos in the preliminary report HERE.

PERSISTENT SLAB AVALANCHES:
The Lipps slide was believed to be a persistent slab that broke in weak faceted snow 1-2′ below the surface. This set up exists South of Turnagain Pass (including Johnson Pass and Lynx drainages). There is a variety of weak layers that sit 1-3′ below the surface and triggering a slab breaking in the old snow remains possible. Pay attention to:

  1. Whumpfing / collapsing
  2. Cracking in the snow
  3. Hard stiff snow over softer old sugar snow
  4. Thin areas of the slab – these are likely trigger points
  5. These avalanches can occur when no signs are present as well – more reasons to follow safe travel protocols.

Photo from the Lipps avalanche yesterday taken by a member of the group involved. We thank these folks for their willingness to share.

Weather
Fri, December 30th, 2016

Mostly overcast skies covered the region yesterday. Ridgetop winds were light from the North and East and no precipitation fell. Temperatures rose dramatically from single digits at 7am to 20F by 7pm (in response to a warm air mass moving through from the West).

Overnight, we have seen light snowfall in Girdwood, Turnagain Pass and Summit Lake as a warm storm system impacts Southcentral. This system looks to be favoring the Girdwood and Western Kenai Mountains, including Summit Lake, snowfall totals mentioned above and in chart below. Another 1-3″ of snowfall is forecast for today before skies begin to break up. STRONG Westerly ridgetop winds (30-45mph) are expected during today bringing cold air – it should be chilly and blizzard like on the ridgelines!

Tomorrow, the cold single digit air mass will remain over us with clear skies and no precipitation expected.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 19   2   0.2   39  
Summit Lake (1400′) 17   3   0.3   12  
Alyeska Mid (1700′) 20   3   0.3   29  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) Under Repair   Under Repair     Under Repair     Under Repair    
Seattle Ridge (2400′) 17   SE   15    33
Observations
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Date Region Location
02/25/24 Turnagain Observation: Kickstep NE Bowl
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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.