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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, December 5th, 2016 - 7:00AM
Expires
Tue, December 6th, 2016 - 7:00AM
Forecaster
Aleph Johnston-Bloom
Avalanche risk The Bottom Line

The avalanche danger is  MODERATE  on all slopes near and above treeline.  Triggering a slab avalanche 1-2+’ thick is still possible and the likelihood goes up as one travels to areas  that have had less traffic this season.  This is due to a buried layer of surface hoar that remains reactive. Additionally, triggering a wind slab avalanche is also possible today on steep slopes that have recently been loaded by winds.  

Special Announcements

There is a FREE Avalanche Rescue Gear discussion at the Alaska Avalanche School (1025 Orca St, Unit N, Anchorage) TONIGHT from 7-9 pm. Come join the conversation!  

Interested in forecasting snow/weather conditions for your day in the backcountry, or your weekend trip? Join CNFAIC forecaster Wendy Wagner Tuesday night for a FREE  mountain weather talk  at Ski AK in Anchorage – 6:30-8pm!!

Planning on taking an avalanche class? The Friends of the CNFAIC is offering two avalanche scholarships through the Rob Hammel fund. Both scholarships are for $500. One is for avalanche professionals and the other is open to anyone!  The deadline for both scholarships is Dec 15th! For more information click this link HERE.  

Mon, December 5th, 2016
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
0 - No Rating
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

Clear skies are allowing folks to venture further into the backcountry and people are choosing to go into steeper terrain. Remember the buried surface hoar as you get into areas that haven’t been ridden. These ‘less traveled slopes’ are the most likely places to trigger an avalanche. The layer of buried surface hoar (from Nov. 16) sits roughly 1-2+ feet below the surface and it is still a concern. Observers have been still been able find this buried persistent weak layer in snow pits throughout the region and it is still reactive in stability tests.  It’s a complicated situation since slopes that have avalanched are generally stable, but those that have not remain unstable. Telling between the two may be difficult as subsequent snow and wind have covered up the evidence. Continue to be on the lookout for signs of instability, cracking and collapsing. A group on Seattle Ridge reported large whumpfs when they were traveling off the main skin track. Manage your terrain and use safe travel protocols. Always ask the question what if this slope slides? What are the consequences? Where will I end up? 

  • Expose one person at a time
  • Group up in safe zones
  • Have an escape route planned
  • Watch your partners and where other groups are around you

Snow pit from November 3rd illustrates the buried surface hoar issue. Photo: Wendy Wagner

Avalanche Problem 2
  • 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

It is hard not to feel and/or see the effect that winds that blew after Wednesdays storm had on the snow once you get into any open terrain. Wind slab avalanches remain a concern on all exposed slopes where winds have formed drifts and slabs. There is a lot of wind effected snow out there and many of the slabs found over the weekend felt stubborn and hard to move. On Friday, one party found a touchy slab on a steep North facing shoulder of Cornbiscuit that released on a ski cut. This is a good example of not letting your guard down even if you see no signs of instability. A big thanks to the party that wrote in, you can read their account HERE. The wind slab may also overlay the buried surface hoar and triggering may release a deeper more dangerous slab if you find the wrong spot. Be wary of hard over soft snow, hollow sounds and steep slopes with obvious depostion in the start zone. 

National Avalanche Center example of Cross Loading

Photo from Eddies yesterday shows wind loading and a small pocket of wind slab. Photo: Andy Moderow

  

Weather
Mon, December 5th, 2016

Yesterday skies were clear and it was cold. Temperatures hovered around 0F and light N winds added to the overall chill. Overnight temperatures in the valleys dropped into the negatives while ridgeline weather stations showed temperatures rising into the teens due to an inversion. Winds were light and variable.

Today will be mostly clear with clouds building in the evening as the next pulse of moisture moves over the area. Temperatures will be in the low teens and East winds will be light. Tonight will be mostly cloudy with a chance of snow showers. Temperatures will be in the single digits but rise overnight. Winds will continue to be light and easterly.  

Tomorrow will be mostly cloudy with a chance of snow showers, temperatures in the low 20Fs and light east winds. The NWS forecast describes the overall pattern for the remainder of the week as cold and dry due to a blocking pattern that will keeping the cold air mass over us.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) -1    0  0 22  
Summit Lake (1400′) -3  0  0  4  
Alyeska Mid (1700′)  1  0  0  11

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  -2 NNE   7   17  
Seattle Ridge (2400′)  7 variable   3   13  
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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.