Turnagain Pass RSS

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ARCHIVED - Forecasts expire after 24 hours.
Issued
Wed, January 25th, 2017 - 7:00AM
Expires
Thu, January 26th, 2017 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

There is a  MODERATE  avalanche danger in the mountains surrounding Turnagain Pass. Wind slab avalanches around 1-3 feet thick will be possible to trigger above treeline on slopes that were loaded over the past few days. In the lower elevations (below  2,000′, such as the Placer Valley area), watch for persistent soft slab avalanches 1-2 feet thick that could release on a layer of buried surface hoar. Watch for changing conditions. If the approaching storm arrives earlier in the day than forecasted the danger could rise to  CONSIDERABLE. Watch for the winds ramping up and precipitation intensity increasing.
Expect the danger level to rise to HIGH  overnight as a strong storm impacts the advisory area.  

Practice safe travel protocols, always carry rescue gear and please let us know what you see out there!!!  

Girdwood Valley:  Slabs have the potential to be larger due to more snow that has fallen on a weaker snowpack compared to Turnagain Pass. Avalanches are running to the ground.    Heighten avalanche conditions exist. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential today if venturing into this area. It will be important to keep slope angles less than 35 degrees and avoid being under big runout zones.  Triggering a slab 3′ thick or deeper is more likely in Girdwood and should warrant extra caution!!!  Also heads up for roof avalanches as rising temperatures will make these unsupported slopes unstable.

Placer Valley: In the lower elevations (below 2,000′) watch for persistent soft slab avalanches up to 2 feet thick that could release on a layer of buried surface hoar.  

Summit Lake:  Rising temperatures, recent snowfall and a generally weaker snowpack has the potential for dangerous avalanche conditions.  Please check out the Saturday Summit Summary  HERE.  

Special Announcements

Dangerous avalanche conditions exist in many area around Southcentral Alaska including the Anchorage Front Range, Hatcher Pass, and Southern Kenai Mountains.  

  • Click  HERE  for details about a skier triggered avalanche in South Fork Eagle River.  
  • Click  HERE  for the Hatcher Pass Avalanche Center advisory and  HERE  for recent snowpack observations.
  • Attention! If heading to the Southern Kenai Mountains, including the Lost Lake zone, this region is out of the advisory area but received 3-5 feet of snow from Saturday’s storm  that has fallen on a reported thin/weak snowpack. There were several avalanches observed after the storm.  
Wed, January 25th, 2017
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
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
  • 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

Monday Northeast winds on Sunburst weather station recorded sustained 30-40 mph winds with gusts in the mid 70’s mph. These strong Easterly ridge top winds combined with 8” of new snow have loaded leeward slopes in the Alpine. There was also plenty of snow available for transport and these wind slabs have the potential to be 1-3’ thick on leeward features. In many places in the alpine these wind slabs are resting on old hard wind crust from the wind event prior to this weekend’s storm. This combination was found in steep terrain in the upper elevations over the weekend where several skier triggered avalanche occured. Today it will be best to avoid loaded slopes steeper than 35 degrees where it will be possible to trigger a wind slab avalanche. Look for areas of pillowed or drifted snow and avoid cornices. Feel for hollow feeling snow, stiffer snow over softer snow or slab sitting on hard snow and watch for cracks that shoot out from your snowmachine, skis or board. 

 

 

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 variety of persistent weak layers exist within the snowpack and vary across our region. In the core Turnagain pass terrain these layers have been generally dormant. However Girdwood Valley had a significant natural cycle Monday night that was observed yesterday. Large avalanches are running on basal facets and sliding to the ground. Slopes around Girdwood that have not slid are suspect for human triggering today.

Throughout the advisory area we are concerned about loading these older layers. In parts of the terrain where the snowpack is shallow there are developed basal facets and in many locations there is a mid-pack layer of facets from December. At the lower elevations, below 2,000′, a layer of buried surface hoar exists under the last two snowfall events (1.5-2 feet below the surface). Slab avalanches failing on this layer are possible today where the snow on top is stiff enough to form a slab. Warming temperatures and settling snow have made this the slab more cohesive increasing the potential for a large more connected slab. Observers reported whumpfs on this layer of buried surface hoar at lower elevations yesterday. The lower terrain in Placer Valley is an area where it is possible to trigger a persistent slab avalanche on this layer. All of these weak layers are important to remember as we anticipate receiving a significant load of snow or rain tonight (elevation dependant) into tomorrow!!!

Natural slab avalanche on Penguin Ridge. Photo: Heather Thamm

Additional Concern
  • Announcement
    Announcement

Roof avalanches: Heads up near buildings with loaded roof tops as warming temperatures and possible rain today through Friday will make these unsupported slopes unstable. Many roofs have 2-3’ of heavy dense snow from the last few weeks, which is plenty of snow to bury a child, pet or seriously injure an adult. 

Weather
Wed, January 25th, 2017

Yesterday was mostly cloudy with periods of clearing and good visibility. Temperatures were in the 20Fs at ridge tops and 30Fs in the valleys. A few snowflakes fell in the mountains and some sprinkles of rain below 700′. Winds averaged 10-20 with a few gusts into the 30s in the afternoon.  

Today will be mostly cloudy with snow showers throughout the day. There is a small system moving through in advance of a much larger system that is on track to impact the area tonight into tomorrow. 2-6″ of snow is forecasted to fall today. Winds will be easterly 15-25 today with gusts into the 30s. Tonight winds are forecasted to increase with gusts into the 70s. Temperatures will be in the 30s and are expected to increase as warm moist air and winds move into the region. Precipitation will be a mixture of rain and snow depending on elevation. There is still some uncertainty about rain/snow line in this system. Expect periods of heavy precipitation intensity overnight. Snow totals will depend on temperatures but 2″ of water is predicted by tomorrow morning. The storm will continue into the day tomorrow and there is an unsettled weather pattern into the weekend.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 34    0  0 50  
Summit Lake (1400′) 30  0  0    23
Alyeska Mid (1700′)  31  2  .2 49  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  23 ENE    14 39  
Seattle Ridge (2400′)  25 SE  13   22  
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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.
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