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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Wednesday, February 18th 2015
Created: Feb 18th 5:52 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
0 NO RATING Below Treeline / Below 1,000'
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The Bottom Line

The avalanche danger is CONSIDERABLE above 2000’ today in the Alpine.  There is currently a weak layer of old snow sitting under a fresh new load from Feb. 16th. Triggering an avalanche 1-3’ thick is likely on terrain steeper than 35°. Below 2000’ the avalanche danger is MODERATE where a different snowpack structure exists and a breakable crust is present.

We would like to stress the need for patience and abstaining from temptation. Today obvious signs of instability are likely as you travel into the Alpine. Watch for recent avalanches and listen for whoomphing sounds. Even if you do not observe these signs don’t be tempted to ski/ride in terrain steeper than 35°.


Primary Concern


Tincan Feb.17, 2015 ETC

Two days ago a warm and windy storm produced hurricane force winds leaving the Kenai Mountains and Western Chugach mountaintops coated with a thick layer (1-3') of new snow in the Alpine above 2000’. Temperatures were warm during this two day storm and rain/snow line fluctuated between 1500-2000’ causing snow below this elevation band to become saturated by rain. Sunburst weather station experienced several hours of 80 mph winds from the East, with a gust measuring 129 mph, which damaged the Sunburst anemometer.

Snow totals from this two-day storm averaged 2’ in the Turnagain Pass area with closer to 3’ in the upper elevations of Girdwood and the Portage area. Summit Lake received slightly less snow, but even 1’ of new snow still warrants a similar level of concern. Slab depths are variable, 1-3' deep, depending on terrain features and its exposure to the wind.  You will also find places where the wind has left some features scoured.  

This is not your typical Chugach maritime snowpack! A very unstable weak layer of faceted snow is buried beneath this1-3’ slab. This weak layer is widespread above 2000’ throughout our region and has shown significant propagation potential after the storm ended on Sunday night. Three remote triggered avalanches occurred simultaneously on a Southern aspect at about 2500 of Tincan’. A skier-triggered avalanche was also reported on Tincan yesterday, lower in the trees near 2100’, with a 1.5’ slab that propagated 20-30’ across a small terrain feature. Luckily no one was caught or injured. These two separate incidents confirm that a human is enough to tip this delicate balance. This problem will not be going away quickly and is the reason we will need to refrain from tempation and stay off of slopes steeper than 35° in the coming days as this weak layer adjusts to it's new load. 

These three remote triggered avalanches occured while digging a snow pit on an adjacent lower angle slope on Tincan's South face. Photo by John Sykes

Travel Advice:

Remotely triggered avalanches are possible today and could be triggered from both above and below. Pay attention for other groups and be aware of run-out distances.

In areas with short steep rollovers, watch out for terrain traps.  A slab if triggered on a small slope in the wrong place, could be enough to bury a person.  

Large collapsing sounds will be your first red flag warning sign. If you hear “woomphing” sounds this is a sign that your weight is enough to collapse the weak layer below and reinforces your decision to stay off of all slopes greater than 35° today. 


Additional Concern

The combination of new snow, warmer temps, and sun affect could be enough to heat up the surface snow on Southern aspects today. On steeper slopes this could produce moist loose point-releases. If you are keeping it under 35° this will be an additional hazard to observe from low consequence terrain. Rollerballs and snow sticking to the bottom of your skins will be the first signs that surface snow temperatures are heating up.  

Natural slab avalanche activity is unlikely today, but should a moist loose avalanche pick up enough volume, it could trigger a slab in steep terrain. 


Mountain Weather

No new precipitation was recorded yesterday. Cloudy skies in the morning became mostly sunny in the afternoon. Winds were light to moderate averaging 15mph from the South on Seattle Ridge. Sunburst wind data was not available yesterday due to damage caused from high winds the day before. We will try to get this fixed when it becomes safe to access this terrain. 

Overnight temperatures were in the 20’s F and no precipitation was measured. Wind data was not available after 10pm last night when Seattle Ridge weather station wind sensor malfunctioned.

Today Sunny skies are anticipated for today and temperatures could reach the mid 30’s F with solar affect from the sun. Winds are expected to be light to moderate (10-20mph) from the South. Precipitation is unlikely.

*Wind data from Seattle Ridge weather station was not available after 10pm on Feb.17.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  43 
Summit Lake (1400') 28 
Alyeska Mid (1700') 32  24 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  N/A  N/A  N/A 
Seattle Ridge(2400') 25  *S   *15 *31 

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

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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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