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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, December 7th, 2015 - 7:00AM
Expires
Tue, December 8th, 2015 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

A generally LOW avalanche danger exists in the mountains surrounding Turnagain Pass. Triggering an avalanche is unlikely but not impossible. The most suspect slopes are in steep terrain at the high elevations where someone just might be able to break off a slab 1-2′ thick. Good travel habits, such as exposing one person at a time, watching your partners and grouping up in safe zones are, as always, key ways to minimize risk.

*If venturing into the ‘periphery’ forecast zones, such as Girdwood Valley, Silvertip and Summit Lake areas, more caution is advised due to limited information about the snowpack in these areas.

Special Announcements

Fireside Chat #2 – Avalanche Rescue – Dec 10th!!  Join CNFAIC forecaster Heather Thamm Thursday night from 6:30-8:00pm at the Alaska Avalanche School for a presentation on “Rescue Fundamentals”. A successful rescue of a buried individual can hinge on even a little bit of knowledge, we hope to see you there!

Mon, December 7th, 2015
Alpine
Above 2,500'
1 - Low
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
  • Normal Caution
    Normal Caution
Normal Caution
Normal Caution means triggering an avalanche is unlikely but not impossible.
More info at Avalanche.org

As our extended period of clear weather continues, we are sitting in the “normal caution” phase of avalanche issues. These include:

1- Sluffs on steep slopes. These have been small to medium in volume, but are getting larger by the day as the surface becomes weaker under clear skies.

2- Triggering an outlier avalanche. This would most likely be an ‘unsupported slab’ that sits above a cliff or steep rocky terrain. Check out video HERE for an example.

3- Triggering a cornice fall. The cornices maybe be small(ish) right now, but they are clearly large enough to take you down somewhere you don’t want to go. As always, give them a wide berth.

Photo: You can see the boot pack to the top of Tincan Proper steers clear of the cornices, however it looks as if someone may have triggered a piece of cornice recently from the boot pack, or possibly veering off of it. A good reminder for us to err of the side of caution when traveling near cornices.

Additional Concern
  • 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

Below is a glimpse of the high elevation snowpack (3,700′). We are finding the old faceted snow from the mid-November cold snap being compressed below roughly 1-3′ of dense and hard Thanksgiving snow. Other than Graham’s pit on Friday, we have seen no reactivity in these old facetd. This includes both snowpack stability tests as well as a large number of folks testing the slopes in the region.


“No results” mentioned in pit = a stabilized snowpack.

As we may be approaching the end of our clear spell, we are watching for the next possible weak layer(s) develop – the surface. Check out the recent reports for more on this HERE.

Weather
Mon, December 7th, 2015

Yesterday was another stunning day in the backcountry; sunny skies, calm winds and temperatures in the mid 20’s F. This was all above the fog and inversion. However, down along the road corridor, temperatures in the single digits existed along with valley fog extending up to 1,500′.  

Today (and tomorrow) will be much the same, mostly clear skies with valley fog. Winds should remain light and variable yet are forecast to increase from the East tonight to the 10-15mph range. Temperatures will again be in the mid 20’s F on the ridgetops and in the single digits in the parking lots  – that’s quite an inversion.

Our next shot for snow looks to be Thursday or Friday. Stay tuned!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 17     0     0   24  
Summit Lake (1400′) 5    0  0 11  
Alyeska Mid (1700′) 17    0   0   14  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′)  26   E   2   10  
Seattle Ridge (2400′) 19 N/A   N/A   N/A  
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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.