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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Sunday, February 19th 2017
Created: Feb 19th 4:19 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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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The Libby Group
Special Announcement

Recent heavy precipitation, strong winds and warm temperatures have created dangerous avalanche conditions in the Southern Kenai; this includes the Seward zone (Lost Lake/Carter/Snug Harbor/etc).  Cautious route-finding is recommended.  

Other regions throughout Southcentral, AK including Chugach State Park and Hatcher Pass have heightened avalanche conditions. There were two skier triggered avalanches on the same slope in the South Fork of Eagle River Friday, please take a minute to read the report HERE if you are thinking of heading to these areas this President's Day Weekend. Also, don't forget to check the Hatcher Pass Avalanche Center's Saturday morning forecast!


The Bottom Line

The avalanche danger is rated CONSIDERABLE due to a thin layer of weak snow 2-4+ feet below the surface. Triggering a slab avalanche breaking in this layer and taking out the top few feet of snow will be likely on slopes steeper than 35 degrees at elevations above 1000'. These slab avalanches may be triggered remotely (from the side, above or below) as well as propagate across entire bowls. Cornice falls are also a concern and will have the potential to trigger a large slab below. If the sun comes out, solar radiation may trigger wet loose sluffs as well as increase the likelihood for triggering a large slab.

Below 1,000' the danger is LOW due to snowpack composed of hard crusts.

**The avalanche conditions we are dealing with this President's Day Weekend have the potential to be unsurvivable and call for cautious route-finding and conservative decision-making. These avalanches can release when there are no red flags present and several tracks are already on a slope.

Summit Lake:  An unstable snowpack persists in the Summit Lake area, make sure and check the Saturday Summary HERE


Primary Concern

There was one confirmed human triggered avalanche yesterday on the buried surface hoar that is the main concern this weekend. A snowmachiner on Seattle Ridge triggered a 1.5-4' deep avalanche on a small WNW slope at 3000'.  The snowmachiner was on the slope and it broke above him but he was able to ride off to the side. This incident really illustrates the potential of this layer and the reason to avoid steep terrain and large or high consequence slopes (ones that slide into terrain traps). The layer of surface hoar and/or near surface facets buried under the Valentine's Day Storm has been found in almost every snow pit that has been dug throughout the advisory area since the storm. Observations from Friday continue to confirm that the layer is reactive and triggering a slab avalanche on the steeper slopes is likely. On Wednesday, there were several remotely triggered slabs on this layer in the Girdwood Valley.  This could be a tricky situation since the pack may 'seem like it feels fine' and people could get away with riding/skiing steeper terrain before a slope breaks. Slopes that saw higher traffic last weekend could remain intact while an adjacent slope slides. Triggering this set-up in spots where the slab is thinner will be more likely and adds to the overall spookiness. In one spot the layer could be a foot below the surface and in another 4' deep, the slab being connected across the slope and the weak-layer being fairly uniform is why the avalanche danger remains elevated. 

What to keep in mind if headed to the mountains:

  1. These slabs can be triggered remotely, from the ridge, the side or below
  2. In terrain that saw high traffic last weekend, this layer will likely be more stubborn to trigger, but don't let that lure you into thinking the pack has stabilized
  3. No obvious signs on instability, or red flags, may be present before a slab is triggered
  4. This is the kind of avalanche that could have several tracks on the slope before someone finds the right trigger point (thin areas of the slab). 

What can we do? Terrain management is the key for hedging our bets. This is simply sticking to lower angle slopes, under 35 degrees with nothing steeper above you.

Snowmachine triggered avalanche on Seattle Ridge that occured yesterday. Photo: Bryan Pfaender

The February 9th buried surface hoar layer (with some preserved stellars) was the culprit in this avalanche. Photo: Bryan Pfaender

Solar effects from SUNSHINE??

If the sun shines and winds are calm, solar radiation can be significant this time of year. Wet/damp loose sluffs on steep South aspects are likely when we do get this first shot of warmth. Additionally, the warming surface snow can enhance the likelihood of triggering a slab. Avoiding sun baked slopes this weekend will be recommended. These Southerly aspects likely have a crust under the new storm snow with either buried surface hoar or near surface facets on top - creating a perfect slab/weak layer/bed surface set up.

Surface warming on Seattle Ridge yesterday. 

 


Secondary Concern

Cornices have grown and changed shape following the Valentine's Storm. These could be teetering on the balance and could break further back than expected. If one does fall it may trigger a slab avalanche below, potentially creating a very dangerous situation if a person is involved. Yesterday there were a few places where chunks of cornice had released. If the sun comes out again today, warming can loosen these beasts and increase the potential for them to break. Remeber these often break much further back than expected. 

 

 

Cornice hanging over steep terrain on Wolverine ridge. Note the slab that was triggered looker's right. 

Another concern that needs to be avoided is travel under glide cracks. A new one was observed yesterday on Seattle Ridge.  Remember these release without warning. 


Additional Concern

Lurking at the bottom of the snowpack are various layers of facets with varying degrees of strength. In the Summit Lake zone and some areas in Girdwood Valley and Johnson Pass depth hoar has been found. Last week's storm cycle tested these layers and only a few avalanches that we know of broke in the deeper layers (Girdwood Valley, Portage Valley and Summit Lake). These layers will be tough for people to trigger, but possible in shallow snowpack zones. More likely is the case where an avalanche occurring in the upper layers of the pack will have the potential to step down and release the entire snowpack. If this does happen the volume will be large and could run long distances. The possibility of these large avalanches is another reason for conservative terrain choices. 

 


Mountain Weather

Yesterday was mostly sunny with some scattered clouds across the area. Easterly winds were calm and temperatures were in the low 30Fs to mid 20Fs in the valleys and low 20Fs to teens in the Alpine. Overnight temperatures dropped a little and winds remained calm. 

Today will be partly to mostly cloudy and there is a chance of snow throughout the day. Winds are forecasted to remain light and easterly shifting to the north this evening. Temperatures should be similar to yesterday and then cool a bit more tonight. 

Tomorrow will partly cloudy and stay a little cooler.  An "active trend" is on tap for the coming week. Stay tuned for details. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  26 71 
Summit Lake (1400')  24 0 31 
Alyeska Mid (1700')  27 0 0 64 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17  ENE   20
Seattle Ridge(2400') 20 rimed  rimed  rimed 

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: May 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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