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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Monday, February 6th 2017
Created: Feb 6th 5:43 am
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
Special Announcement

Many areas around Southcentral, Alaska including the Southern Kenai Mountains, Seward, Snug Harbor and Lost LakeAnchorage Front Range, Hatcher Pass continue to have an unstable snowpack. Human triggered large avalanches, breaking near the ground, are possible. Please see link above for recent activity. Keep in mind avalanches can be triggered remotely, from below or mid-slopeCareful snowpack evaluation and cautious route-finding is essential. 

Mark your calendars: This weekend CNFAIC and the Anchorage Snowmobile Club will be hosting a FREE Avalanche Rescue Workshop at Turnagain Pass, 11am -12:30pm in the Motorized parking lot. We will focus on practicing with your avalanche beacon, probe and shovel. This workshop is open to everyone and anyone, novices and experts, that recreate in avalanche terrain – snowmachiners, skiers, snowboarders, etc… Click HERE for more details. 

 


The Bottom Line

The avalanche danger in Turnagain Pass is MODERATE above 1500’ where triggering a persistent slab avalanche 2-4+ feet deep is possible and consequences remain high should you find a trigger spot. Additional avalanche problems to be aware of are wind slabs, cornices and loose snow avalanches - heat from the sun could make these easier to trigger. Be sure to carry your rescue gear and practice safe travel protocol - such as exposing one person at a time, grouping up in safe zones, having escape routes planned and watching your partners!  

Below 1500’ the danger is LOW, where a hard crust has stabilized the snowpack.  

Summit Lake and Girdwood: An unstable snowpack exists and human triggered avalanches breaking near the ground are possible. Make sure and check the Saturday Summit Summary HERE.


Primary Concern

Clear skies, soft snow and warm weather provided just the right conditions for a busy weekend in Turnagain Pass. Lots of steeper terrain was tested on both side of the road (non-motorized and motorized) and confirmed our primary concern: Large persistent slabs are stubborn to trigger, but can propagate with enough force and/or if a person finds just the right trigger spot. On Friday there were two separate snowmachine triggered avalanches in the Turnagain zone. One in Seattle Creek where a rider was completely buried except for his hand sticking out. His partners, who were watching from a safe zone, located him in minutes. He was uninjured. In Lynx Creek a snowmachiner triggered a slope just after he crested a hill but was not caught. No obvious signs of instability were observed and in both cases there was already tracks on the slope. 

These avalanches were triggered on an old/weak foundation, facets near the ground. This upside down, poor structure exists in many places across our forecast zone, but not on every slope. Spacial variability of our snowpack, varying depths and inconsistency of the weak layer, make for difficult and near impossible assessment of an entire slope. This type of avalanche is often triggered in a thin part of the slab, near rocks or on the edge of the slab. These can also be triggered by multiple skiers/boarders and/or snowmachines on, near or under slopes. This speaks to the uncertainty of our current avalanche problem and the dangers of a stabilizing snowpack. Remember many steep slopes have tracks on them, this does not mean all of these slopes are safe. It may be the 3rd or 10th or 25th track that tips the balance. The likelihood of triggering a deep persistent slab is decreasing, but the consequences remain high should you find the wrong spot. This kind of MODERATE danger has an element of “rolling the dice” and does not make for easy decision making. If you decide to venture onto bigger terrain please keep in mind: 

  1. Large slopes have the potential to produce large propagating avalanches.
  2. Obvious signs like shooting cracks or collapsing “whumpfing” are unlikely.
  3. Identify safe zones and travel one at a time between islands of safety.
  4. Watch your partners and be aware of other groups above and below you.

A view from the Seward Hwy of the avalanche triggered in Seattle Creek on Friday, 2/3/17. This is near -3 bowl, East of the Headwall. 


Additional Concern

Over the last few days the sun has been affecting the snow on Solar aspects (East - Southeast - South.) Small sun induced rollerballs and a few point releases have been observed as well as a sun crust on some Southern aspects. Today light SE winds should keep snow surfaces cool, but should the sun have some heat keep in mind it could make the following additional avalanche concerns easier to trigger:

Wind Slabs: An observer yesterday reported a period of light winds drifting snow onto leeward aspects. New shallow wind slabs may be tender, or it may still be possible to find an old stubborn wind slab on leeward slopes. Look out for pillowed or drifted snow and avoid areas with stiff snow over soft snow. Warm temperatures and direct sunlight may make these slabs easier to trigger on solar aspects.

Loose snow: With 4-8" of loose snow on the surface over a dense base, watch your sluffs and watch how the sun is affecting the snow around you. These may pack enough punch to push you somewhere you don't want to go i.e. a terrain trap. 

Cornices: This weekend cornice cracks were reported along the back bowls of Seattle Ridge making some of these cornices extra sketchy. Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche on the slope below. Give cornices extra space and avoid being under them. 

Sluff under ski tracks on Lipps SW face as seen yesterday. This slope experienced warming from the sun and roller balls can be seen under rocks. This is a good example of terrain that likely harbors an unstable foundation and has the potential for a large propagating avalanche.

 


Mountain Weather

Yesterday inverted ridge top temperatures reached a high of 34F in the morning and were dropping throughout the day into the upper 20F’s. Pockets of cold air in valley bottoms averaged in the teens F. Ridgetop winds were light to moderate from the East, 5-20mph. No precipitation has been recorded in many days.   

Today expect a similar weather pattern. The upper elevations are expected to be in the mid to high 20F’s and valley temps will remain cooler, in the teens F’s.  Expect sunny and clear skies with light to moderate SE winds (10-20mph.) This pattern is expected to last over the next few days with temperatures cooling off. Our next chance for snow flurries may be as early as Thursday or Friday. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29  53 
Summit Lake (1400') 14  22 
Alyeska Mid (1700') 28   47

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 29  16 
Seattle Ridge(2400') 29  ESE  11  24 

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 25, 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
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
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