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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Thursday, February 16th 2017
Created: Feb 16th 5:11 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.
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Deuter USA
Special Announcement

Recent precipitation, strong winds and above freezing temperatures have heightened avalanches conditions throughout Southcenral, AK including Anchorage Front Range, and Hatcher Pass. On the Southern Kenai including Seward zone (Lost Lake/Carter/Cresent) an active weather pattern is currently impacting this area creating dangerous avalanche conditions. Travel is not recomended.

Click HERE for a near miss report following a large avalanche triggered by a snowmachiner in Lynx Creek in early February. Luckily no one was caught in this avalanche. We want to extend a big thank you to all those involved and willing to share their story.

Have you purchased your tickets yet for the 3rd Annual SNOWBALL?? This event is almost sold out. Get them while you can, HERE!! Come out, get your groove on, win some door prizes, bid on some amazing silent auction items and support avalanche safety and education! All proceeds to benefit Alaska Avalanche School and Friends of the Chugach National Forest Avalanche Information Center.


The Bottom Line

The avalanche danger is CONSIDERABLE above 1000’ around Turnagain Pass, Placer Valley and Girdwood due to a variety of concerns. Natural avalanches are possible and human triggered slab avalanches 3+’ thick are likely on slopes steeper than 35 degrees. Fresh wind slabs and loose snow avalanches will also be easy to tigger and should the sun appear, these may release naturally. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential today.

Below 1000’ the avalanche danger is MODERATE where an avalanche from above is possible as well as triggering a loose snow avalanche. 

Summit Lake: Expect the avalanche danger to remain elevated due to recent a recent storm that has impacted our region. Click HERE for the weakly Summit Lake Summary.  


Primary Concern

In the past 3.5 days Turngagain Pass has received 3.1 inches of water (SWE) and just under 4.0” SWE was recorded in Girdwood. This water weight (either as snow or rain) combined with strong winds caused a widespread natural cycle as well a variety of lingering avalanche concerns. Yesterday all three red flags were observed between Girdwood and Turnagain Pass in the afternoon as clearing skies allowed for a good look around. In addition to dozens of mid-storm avalanches observed, several natural slabs released in the afternoon in Girdwood. There was also a report of a remote triggered avalanche in the Girdwood Valley. Very loud collapsing (whumphing) was experienced in Turnagain Pass and upon investigation was caused by surface hoar collapsing 2-3’ below the surface. Heat from the sun caused numerous natural loose snow avalanches in steep terrain on South and Southeast aspects. Today expect similar conditions as more unsettled weather is expected to bring another 4-10” of new snow accompanied by Easterly winds averaging 15-25mph, enough to actively be loading leeward features. Although the sun is not anticipated today, should it appear, there is enough solar energy to make the following concerns easier to trigger. Be aware of the following recent storm snow instabilities:

Wind Slabs: Expect fresh wind slabs up to 1’ thick to be tender on leeward features today. It will also be possible to trigger an older, much deeper wind slab 3+’ thick on a variety of aspects. These wind slabs may be sitting on top of weak snow (buried surface hoar) and/or a slick bed surface (old sun crust on Solar aspects) and may propagate further than expected. 

Loose Snow Avalanches: Loose surface snow “sluff” will be easy to trigger, and may release naturally if the sun appears today.

Triggering a wind slab or loose snow avalanche will be likely today on slopes steeper than 35 degrees.  It is also important to remember natural avalanche are still possible. Avoid being in avalanche runout zones and remember that recent avalanches, cracking and collapsing (whumpfing) are obvious signs the snowpack is unstable. 

Natural avalanche activity over the last few days on the SE face of Seattle Ridge. There are still places like the slope above the uptrack that did not slide on this aspect. 

 

Cracking was obsevered on a steep unsupported test slope yesterday on Tincan, West aspect at about 2000'. 

 

Beware there is not a lot of info about the new snow/old snow interface, but there are places where wind slabs 3+' thick are sitting on buried surface hoar and could propagate large avalanches. FYI - the two upper rain crusts in this photo were not found above 2000', but the sun crust was observed in the upper elevations prior to this storm.

 

 


Secondary Concern

Cornices have been growing over the last few days due to strong winds and heavy snowfall. These may release naturally or with the weight of a person. If you are along a ridge, cornices can be difficult to see, and can break further back than expected. Avoid being under or above these very unpredictable and precariously perched features.


Additional Concern

Weak snow (facets and depth hoar) in the lower layers of the snowpack continues to be a concern in our advisory area. Avalanches occurring in the upper layers have the potential to step down and release the entire snowpack in some places. If this does happen the volume will be large and could run long distances. As more and more weight is added to the snowpack this becomes more of a concern. A few of the naturals throughout this last storm looked to have run into older faceted snow. The possibility of these large avalanches is another reason for conservative terrain choices today. 

Sevearl natural slab avalanches on a SE aspect of Fishes Breath in Girdwood Valley, including one that stepped down into an older layer of the snowpack. Photo courtesy of Mike Welch

 


Mountain Weather

Yesterday morning 6” of new snow fell before 9am at all elevations. By late morning skies were clearing and remained partly cloudy for most of the afternoon. With the exception of solar warming felt on South and East aspects, temperatures remained below freezing most of the day. South winds shifted to more of an Easterly direction late morning and average 15-25mph with some gusts in the 40’s by early evening. Overnight an additional inch of snow was recorded.

Today expect mostly cloudy skies and scattered snow showers throughout the day. Temperatures are expected to hover around 32F near sea level and an additional 4-10” of snow (up to .5 inches of water/SWE) is possible today. Easterly ridge top winds are expected to average 15-25mph with gusts in the 40’s mph. An additional 5-12” of snow is possible this evening.

Similar weather is expected to persist over the next few days and into the weekend with a continued pattern of scattered snow showers and temperatures remaining below freezing (32F.)

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28  .1  73 
Summit Lake (1400') 26  .1  27 
Alyeska Mid (1700') 27  .44  67 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 18  ENE  18  54 
Seattle Ridge(2400') 22  n/a  n/a   n/a  

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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