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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Tuesday, January 19th 2016
Created: Jan 19th 5:40 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
The Bottom Line

The avalanche danger is MODERATE at and above treeline today where fresh wind slabs have formed yesterday afternoon/ overnight with the approach of a quick but intense burst of heavy snow and moderate easterly winds.  These will be possible for a person to trigger, specifically in steep, wind-loaded terrain above treeline.  Wind slabs are expected to be in the 12-18” range.  In the mid-elevation band (at treeline), glide cracks continue to pose a significant threat.  Limiting or avoiding your time spent under glide cracks will be your best bet to mitigate this particular avalanche problem.


Primary Concern

Yesterday afternoon/ evening ushered in a quick 8-hour period of intense snowfall in the Turnagain pass area where we picked up around 6” of new snow.  Snow fell in earnest above about 300’ as ridgetop winds kicked up from the northeast.  This new snow in addition to 6-8” of low-density snow from Saturday afternoon/ Sunday morning is enough to build shallow but tender wind slabs on steep, leeward slopes.  Expect wind slabs to be in the 12-18” range and may prove easy to trigger in the alpine.  Above treeline, slopes greater than 35 degrees with a south or west facing tilt will be most suspect today.  How this new snow/ fresh wind slabs bond to yesterday’s surface will be key to watch for and can be sussed out by utilizing quick hand pits or small (no consequence) test slopes. 

At and below treeline, the wind is playing less of a role on this new fallen snow.  Expect yesterday afternoon’s storm snow to settle out quickly.  There may be a few point releases or some roller ball activity in this elevation band but the greater concern will be glide avalanches (more on that below).

Snowfall rates were intense (1"/ hour) toward the end of the day at Turnagain Pass yesterday.  Rain/ snow line hovered around 300' with a rain/ snow mix at sea level.


Secondary Concern

After several days of glide cracks releasing in the Turnagain Pass zone - some of which are 'front and center' on Seattle Ridge and visible from the motorized parking lot, we did not see any signs of new glide avalanche releases yesterday. With a fresh dusting of snow though, these cracks are becoming harder to spot as they fill in with new snow. 

Glide avalanches, though spooky are a pretty easy avalanche problem to mitigate.  Simple avoidance and limiting your exposure to these large cracks is key. Map out any notable glide cracks from a good vantage that may affect your route, and pick a track that minimizes time spent underneath these.  Though the probability is low that a glide will fail with someone on the slope, the consequences remain dire.  Recent glide avalanches have been quite large and almost always take the entirety of the snowpack (to the dirt) out as they fail.  This is evidenced in the dirty debris piles left behind.

Glide cracks can be seen on all aspects in the mid-elevation band (1500-2500'). Here, 3 separate glide cracks litter an E facing slope in Main bowl. Note: With yesterday's 6" of new snow, many of these cracks may be 'dusted over' and much harder to see now.


Mountain Weather

Yesterday started out mostly clear in the morning above about 400’.  Valley fog persisted throughout most of the day around Turnagain arm, Girdwood and Portage Valley where colder air was pooling.  Meanwhile, ridgetop temps were nearing the 32 degree mark at 3800’ (Sunburst).  Winds were light from the East picking up around 3pm (30's mph with gusts in the 50's) as a weakening low pressure system rolled through the advisory area.  Clouds were on the increase throughout the day and snow began falling around 3pm.  Snowfall tapered off before midnight with about 6" falling at the Pass and a rain/ snow mix below 300'.  

Today we can expect mild weather during the daylight hours with temps in the mid-30’s at 1,000’ and ridgetop winds less than 20 mph.  We may ring just a trace of precip out of some departing clouds this morning, but don’t expect it to amount to much. 

Tonight and into tomorrow morning looks to be almost a carbon copy of yesterday afternoon’s short but intense burst of snowfall meaning we may wake up to a few more inches of snow in favored areas such as Turnagain pass by Wednesday morning.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32   6  .5 87 
Summit Lake (1400') 31   .1  26
Alyeska Mid (1700') 33   3  .6  66

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  27  ENE  18 57 
Seattle Ridge(2400')  29  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

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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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