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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, December 19th, 2016 - 7:00AM
Expires
Tue, December 20th, 2016 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

There is a CONSIDERABLE avalanche danger in the mountians surrounding Turnagain Pass, Girdwood Valley and Summit Lake on the Kenai. New snow and strong wind yesterday have loaded a very weak layer of faceted snow and human triggered avalanches are likely on all slopes above 1,000′.  Slab avalanches ranging from 10-20″ could be triggered remotely from ridgelines or valley bottoms. Today’s message is simple: it is a day to play it safe and keep slope angles below 30 degrees with nothing above you.

Conservative terrain management and expert level snowpack assessment will be necessary for any travel in avalanche terrain.  

***Portage Valley ice climbers and hikers: A  MODERATE  danger exists below 1.000′ where there is potential for avalanche debris, from a slide occurring above, to run through gullies.  

Special Announcements

Don’t forget about tomorrow night:  Come to the  Blue & Gold Boardshop for a CNFAIC presentation on the ‘Turnagain Pass snowpack’!! This will be an interesting discussion considering the interesting snowpack! Details on link.

Motorized use:  The Chugach National Forest continues to monitor snow coverage daily for motorized openings. A 36 € base is a general number the Forest uses to determine adequate coverage – this could be more or less depending on snowpack density. Thanks for your patience and don’t let up your snow dance €¦.

Outside of Advisory Area  – Petersville region:
We received a report from the Dutch Hills area noting very unstable snow; several slab avalanches 2′ thick remotely triggered by snowmachiners. If your are headed that way PLEASE see the report and photos HERE.

Mon, December 19th, 2016
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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
  • 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

An exciting day was had in the backcountry yesterday. Both for weather and avalanches. It was a ‘rapid loading’ event as heavy snowfall from 6am till 5pm loaded slopes with medium density snow. Human triggered avalanches were numerous, yet we have not heard of anyone being caught up in these. From what we know, these slides were in “small terrain” which equates to smaller and more manageable avalanches. See all the reports sent in last night HERE – a big thanks to these folks for writing in!!  

Yesterday’s snowfall totals:
     Turnagain Pass:  6-8″
     Girdwood Valley:  5-7″
     Summit Lake:  4-10″ 

The snowpack is showing its hand and it’s not a good one. Weak faceted snow sits under a slab anywhere from 8-20+” thick. The slab is relatively soft and composed of yesterday’s new as well as the 4-8″ that fell during the end of last week. Strong winds have redistributed the snow above treeline and slabs will vary in depth and stiffness. Things to keep in mind today:

  1. You are likely to trigger an avalanche on steeper slopes
  2. You can trigger these from below or from the ridgeline
  3. Facets are notorious for wide propagating slabs and remote triggering
  4. Watch for obvious signs of instability (recent avalanches, cracking and collapsing)
  5. Quick hand pits and poking the snow with your pole (away from a used up-track) are good ways to monitor the slab and weak snow underneath
     

If skies clear enough for travel outside of the trees, another thing to keep in mind:

  • Small terrain = small avalanches = relatively manageable
  • Larger terrain = larger avalanches = unmanageable

 

Photo: Crown of easily triggered 8″ slab avalanche that sympathetically triggered three more small slabs on the other side of the gully. If you look closely you can see one in the background. More on that in video below. This is the definition of a ‘touchy’ snowpack.

  

Photo: Soft slab avalanche into a terrain trap in the Tincan Trees (left side of photo). Small terrain – small avalanche. Thank you to Kakiko Ramos-Leon for the photo. 

 

Photo: Remote triggered shallow slab avalanche on a rollover in the Eddies area, Andy Moderow.

 


 

Hopefully by this point you are convinced that once the visibility improves, very conservative travel is warranted in the backcountry. If you get out, please send us your photos and information – we will be monitoring the pack daily but your reports are invaluable!

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Expect cornices to be sensitive and easy to break off. They also are likely to trigger a slab avalanche below. If you choose to walk a ridgeline today, give these a wide berth and be aware of people below you.

Weather
Mon, December 19th, 2016

Yesterday was a bone fide storm day on Turnagain Pass. Heavy snowfall began in the morning and tapered off last night. See the snowfall and water numbers below. Ridgetop winds were strong, averaging in the 20’s mph with gusts into the 60’s. Temperatures were relatively warm; low 20’sF on ridgelines and 30F at 1,000′ in the parking lots.  

Today we can expect partly clearing skies – to some degree – and a chance for localized instability showers. Another 1-2″ of snow could fall where these ‘showers’ take place. Temperatures will be slightly warmer, near 32F at 1,000′ and increase to the upper 20’s along the ridgelines. Ridgetop winds will be light, 5-10mph from a Westerly direction.

For this week, most of the weather is getting pushed South and we should see a mix between clearing skies and localized snow showers.
 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26   7   0.7     30  
Summit Lake (1400′) 26   2 (manual report 4+”) 0.2   10  
Alyeska Mid (1700′) 28   4 0.4   20  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 21    NE 26 67  
Seattle Ridge (2400′) 23   SE   18   42  
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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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