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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Friday, January 27th 2017
Created: Jan 27th 5:23 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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The Bottom Line

HIGH avalanche danger remains in the upper elevation terrain in the Girdwood Valley, Portage Valley and the Kenai Mountains (including Turnagian Pass). Large slab avalanches are expected to occur naturally and debris could run to valley floors. In the mid and lower elevations, a CONSIDERABLE avalanche danger exists where naturally occurring slab avalanches are possible. Travel is not recommended in avalanche terrain. The main storm has passed, but human triggered avalanches will remain likely today. Should you decide to check out the conditions keep slope angles less than 30 degrees and steer clear of gullies and the bottom of large and steep slopes in the event an avalanche occurs above you.


Primary Concern

Finally, a potent wet, warm and windy storm to help build our snowpack and hopefully clean out the many weak layers that have developed this season. Over the last 48-hours we have seen 2-4+ inches of rain fall below 1,000' and 2-4+ feet of snow fall at the upper elevations. The peak of this storm was 24 hours ago (early yesterday morning) and with this was a widespread natural avalanche cycleAlthough the storm is winding down, along with the naturally occurring avalanche cycle, there still exists the possibility for very big avalanches to occur today and human triggered avalanches are likely 

That said, today is another day to leave the mountains alone and let them do their business. We should see one more pulse of wind and precipitation come in later this morning (20-25mph Easterly ridgetop winds and .2" of rain below 500' and 2-4" snow above 500'). Temperatures will remain warm and this is a big factor keeping the mountains unstable currently. At the upper elevations were drier snow is falling and winds are blowing, wind slab and storm slab avalanches are likely. Debris from these could run into the mid and lower elevation bands. Additionally, at the mid and lower elevations the new moist/wet snow is still adding stress to the underlying weak snow and post storm large avalanches lower on slopes are possible. 

Photo:  Large avalanche triggered by avalanche reduction work just South of Girdwood. You can see the wide propagation and various bed surfaces in the crown where the avalanche released. 
 


Powder cloud from reduction work along Seward Highway
 

Visibility was limited on Turnagain Pass, but we did get a look a this new debris pile on the South end of Seattle Ridge.

 

Video below is from avalanche reduction work conducted by the AKDOT & PF Avalanche Program along the Seward Highway between Bird and Girdwood.


Secondary Concern

Many areas in the region have a variety of weak layers in the mid and lower portions of the snowpack. The warm temperatures and additional load from this storm has been overloading these weak layers and we are seeing avalanches break near the ground. This is occurring mainly in thin snowpack zones such as Girdwood Valley, Summit Lake and the interior Kenai Mountains. The South end of Turnagain Pass is also suspect for these large slides breaking near the ground. Hopefully visibility will be good enough today to see what has occurred in these zones.

Photo:  It's a bit difficult to see but this is a natural avalanche breaking near the ground yesterday on Orca with debris running in the middle of the trim line. Orca can be seen easily from the Tesoro gas station in Girdwood. 

 


Additional Concern

Below 1,000' the snowpack is saturated due to 1-3" of rain that fell during the past 36 hours. Wet slab avalanches were occurring naturally yesterday and though the peak of the avalanche cycle is winding down, they are still expected again today with continued above freezing temperatures and .2" of rain forecast.

Photo below:  Slab avalanche triggered by rain and very wet snow between 800' and 1300' on lower Wolverine Ridge. There are likely more of these, but visibility was limited to only a few portions of terrain. NOTE: You can see the rain/snow line by the dark trees at the bottom of photo and white(ish) trees at the top.


Mountain Weather

Yesterday's wet and warm storm diminished during the day and precipitation and winds have backed off overnight. Girdwood Valley saw 1.6" of rain while Turnagain Pass had 1.3". The rain/snow line was around 1,000' and has lowered to around 700' this morning. Ridgetop winds peaked 24 hours ago in the 40's mph with gusts into the 70's from the East. Temperatures were warm, 40F at sea level and 32F at 1,000' with ridgetops in the mid 20'sF.

Today, we should see mostly cloudy skies with another quick shot of precipitation, 0.2" of rain below 500' and 2-4" of snow above. Ridgetop winds from the East are expected to bump up to the 20-25mph range before backing off this evening. Temperatures should stay warm through today, mid to upper-30's at sea level and around 30F at 1,000'.

Starting tonight and into tomorrow, cooler Westerly flow will move in dropping temperatures and allowing the wet snow to begin to freeze up. Stay tuned!

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 34  1.3  65 
Summit Lake (1400') 31  0.7  27 
Alyeska Mid (1700') 32  1.6  60 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  NE  27  67 
Seattle Ridge(2400') 26  SE  Sensor RIMED  78 

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

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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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