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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Thursday, December 10th 2015
Created: Dec 10th 6:13 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
 Show the Complete North American Avalanche Danger Scale
Rossignol
Special Announcement

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". This class is great introduction if you are new to the topic and a terriffic way to refresh your understanding if you have taken a class before!


The Bottom Line

With up to a foot of new snow falling overnight accompanied by moderate winds, we have a CONSIDERABLE avalanche danger above 1,000'. Natural avalanches are possible and human triggered avalanches are LIKELY on slopes over 35 degrees. These will be most pronounced in wind loaded terrain where slabs 1-2' thick have formed. The new snow has fallen on a VERY unstable base and is expected to have a difficult time bonding - this also includes slopes that are sheltered from the wind.

**Very careful snowpack evaluation, cautious route-finding and conservative decision-making is advised if traveling in the backcountry. Patience will be key if skies clear enough today for travel above treeline.


Primary Concern

The GOOD NEWS:  A quick hitting snow event rolled through last night and has, so far, added 10" of new snow at Turnagain Pass. Girdwood Valley has seen slightly less with 8" overnight and Summit Lake much less, only 2-3". When adding last night's total to yesterday's 2-4", we have a 24-hour accumulation of 10-14". This is "low density" new snow which is great news, but that leads us to the 2nd part of the story...

The BAD NEWS:  This new snow has fallen on a VERY weak surface with a hard bed surface below (see photo).  Although it's only a foot of new snow, it will simply have a hard time sticking to the old sugary snow below. Adding to this, avalanches triggered could run far with the help of the hard bed surface underneath. In short, this is classic case for creating very touchy avalanche conditions. This means you are more likely than not to trigger an avalanche if you enter slopes over 35 degrees. The exception are slopes where the new snow is so unconsolidated that it is not forming a slab - in this case, large sluffs can be expected.

Things to watch for if you are headed out:

  • Stiff, harder snow over weak, softer snow
       -  Hand pits are good ways to assess how the storm snow is bonding to the older 'faceted' weak snow
  • Shooting cracks in the new snow
  • Whumphing, or collapsing of the new snow into the weaker snow below

Photo below is from yesterday of the 'weak' faceted snow that sits on top of a hard bed surface. Imagine a cohesive slab of snow 12" thick sitting on top of this weak layer/bed surface combination - yep, that's what we have this morning and it's a problem...


Mountain Weather

Yesterday's light snowfall added 2-3" before intensity increased overnight adding another 10" at mid elevations. (Check out the Turnagain Pass Snow Stake by clicking this link!). Winds have been Easterly and moderate with Sunburst averaging in the 20's mph overnight and Seattle in the teens. Temperatures have decreases slightly with the snowfall as well and are sitting in the mid-20's F this morning on ridgetops.

Today we can expect snowfall to decrease and skies start to break. Winds should remain from the East in the 15-20mph range and temperatures in the mid 20's F at the mid and upper elevations.

Looking to Friday night and weekend, a potent storm system is slated to arrive that could bring "incredible snow rates" to Turnagain Arm and Anchorage - see this NWS discussion HERE.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28  10  34 
Summit Lake (1400')  29   0.2 13 
Alyeska Mid (1700') 30  0.8 23 

 

RIDGETOP 24-hour data (6am - 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 26  NE  16  44 
Seattle Ridge(2400') 27  SE  10  22 

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).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: Mar 15, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: OpenSkookum drainage closes to motorized use on April 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

Subscribe to the Turnagain Area Avalanche Advisory:

The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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