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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, January 2nd, 2017 - 7:00AM
Expires
Tue, January 3rd, 2017 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

A MODERATE avalanche danger remains in the alpine where triggering an isolated wind slab or a deeper slab 2+’ thick is possible on steep wind loaded slopes that haven’t avalanched. Within the trees and at lower elevations there is LOW avalanche danger, where triggering an avalanche is less likely.  

In the periphery zones of Johnson Pass and Summit Lake a much shallower snowpack exists and it may be easier to trigger a slab avalanche in these areas. Check out the Summit Lake Summary  HERE and an observation HERE from Tenderfoot from yesterday.

Special Announcements
  • As of yesterday Alaska DOT has not cleared the Turnagain Pass motorized lot. Please park safely and be respectful of any plow efforts to clear this lot.  

  • If heading to Hatcher this New Year – unstable conditions exist – check the Hatcher Pass advisory  HERE!    Mark your calendars for the FREE rescue workshop at Hatcher Pass on January 14th. More info  HERE.
  • For Turnagain Pass December Weather History Chart click HERE.
Mon, January 2nd, 2017
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
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
  • 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

PERSISTENT SLAB AVALANCHES (In our current case: Hard WIND SLABS SITTING ON WEAK SNOW): A big wind event that occurred on December 30th has stripped many Southern and Western ridgetops and left an unusual loading pattern for our region; loading Northern and Eastern aspects. This wind event as well as the Christmas snow storm (a week ago) caused widespread avalanching in the area. Several persistent weak layers are buried within the snowpack (facets and buried surface hoar), but strong supportable snow may make it tough to find the right trigger spot.  

Some uncertainty remains today with how the warm inverted air temps (approaching 40F) will affect the snowpack in the alpine. Although radiation from the sun at this time of year is minimal, whenever temperatures remain above freezing for 24 hours it is worth keeping in the back of your mind. Be skeptical of supportable and hollow sounding snow on steep slopes. Likely trigger spots will be in thinner areas of the snowpack in steep rocky terrain or on unsupported slopes that haven’t avalanched. Triggering a small isolated wind slab or a deeper slab 2+ feet is becoming more difficult, but is possible for a person or snowmachine to tip the balance. Obvious signs like cracking and ‘wumpfing’ are becoming less common and may not be an early warning sign. 

Before exposing yourself to steeper terrain, ask yourself what will happen if the slope slides? Always practice safe travel habits to minimize exposure in avalanche terrain! 

  • Expose one person at a time
  • Watch your partner from a safe zone
  • Have an escape route planned
  • Watch for other groups

A closer view of the natural avalanches that occured on Corn Biscuit’s North facing chutes last Friday (12/30.) Places that haven’t avalanched with similar characteristics (rocky starting zones, top loading and cross loading) remain suspect. 

 

Most of the snow along Southern aspects have blown away making it unlikely to trigger an avalanche in these areas.  

 

Weather
Mon, January 2nd, 2017

Yesterday skies were sunny and clear with light Northwest winds. A large temperature inversion was observed, 12F at 1000′ and 33F at ridge tops, which caused valley fog in Turnagain Arm.  

Overnight ridge top temps   increased into the high 30F’s Turnagain Pass and low 40F’s in the Girdwood Valley. Valley temps have remained around 10F. Winds have remained light and no precipitation was recorded.  

Today expect a similar inverted weather pattern with above freezing temperatures in the alpine and temperatures near 10F in valley bottoms. This will trap dense Valley fog in and along Turnagain Arm.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 33   0   0   38  
Summit Lake (1400′) 13   0   0   12  
Alyeska Mid (1700′) 31   0   0   25  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 35   W   4   13  
Seattle Ridge (2400′) 36   NW   5   16  
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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.