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ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, January 3rd, 2017 - 7:00AM
Expires
Wed, January 4th, 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 unlikely, but not impossible.

In the periphery zones of Girdwood, 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 click HERE for a recent observation from Max’s Mountain in Girdwood.  

 

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.
Tue, January 3rd, 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. 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
  • 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): Its been 4 days since a big wind event loaded Northern aspects and cross loaded many 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 over top is making it stubborn to trigger. In the periphery areas (Girdwood, Johnson, Lynx, Summit Lake and even Kickstep) where a thinner snowpack exists several observers have experienced collapsing/wumpfing in recent days. Including an observer who felt/heard a loud collapse followed by a fast moving shooting crack on their second ascent up Max’s Mountain on Sunday. It will be in these areas where finding unstable snow may be easier. 

If you were out yesterday you probably noticed an extreme temperature inversion. Some ridgetops reached 40F while valley bottoms remained in the single digits (F). Today looks similar. Luckily this warming trend did not melt the surface snow and radiation is minimal at this time of year. However when temperatures remain above freezing for several days it should warrant caution. Be skeptical of steep loaded slopes that haven’t avalanched yet. Likely trigger spots will be in thinner areas of the snowpack in steep rocky terrain or on unsupported slopes that may harbor just the right set-up for a person or snowmachine to tip the balance. Obvious signs like cracking and ‘wumpfing’ are becoming less common in the Turnagain Pass area and may not be an early warning sign. The problem with hard slabs, as noted by local ski guide and avalanche educator, Joe Stock, “They let you get out in to middle with no feedback, then they crack far uphill from you.”  Be sure to check out Stock’s excellent discussion on Close Calls With Avalanches.

This is why we should 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

These slabs on the North side of Tincan likely released during the Dec.30th wind event. This a good example of where pockets of poor snowpack structure may linger. It is in these places where practicing safe travel protocals is very important. Photo taken 1/2/17

 

Weather
Tue, January 3rd, 2017

Yesterday skies were sunny with light Northwest ridge top wind. A large temperature inversion was observed, valley bottoms were in the single digits (F) and ridge tops reached 40F. A thick valley fog filled Turnagain Arm.  

Overnight ridge top temps dipped slightly into the mid-30F’s and valley temps averaged around 10F.   Winds have remained light and no precipitation was recorded.  

Today expect a similar inverted weather pattern with above freezing temperatures near ridgetops. Northwest ridge top winds are expected to pick up today, 10-20mph. Dense Valley fog may linger in and along Turnagain Arm.  

A dominent high pressure is positioned over Interior and Southcentral, Alaska. The latest weather discussion mentions the potential for strong gap winds Wednesday night thru Thursday and cooling upper elevation temperatures. This could bring a windchill factor well below zero (F.)

An impressive photo taken yesterday of recent surface hoar growth (~4″ long) found on Center Ridge. Don’t worry this on the surface of the snow and doesn’t present any current concerns. Photo courtesy of Sam Galoob

Thick valley fog along Turnagain Pass yesterday was a result of the extreme temperature inversion in our region.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30   0   0   37  
Summit Lake (1400′) 12   0   0   11  
Alyeska Mid (1700′) 29   0   0   25  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 36   NW   4   14  
Seattle Ridge (2400′) 37   NW   4   17  
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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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