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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, December 25th 2017 5:13 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There is a MODERATE avalanche danger today in the alpine and treeline elevation bands where triggering a hard wind slab will be possible on steep, unsupported slopes. Above 3,000’ triggering a much larger and more dangerous avalanche is also possible given the poor structure that we know exists high in the alpine. Obvious clues like ‘whumpfing’ and shooting cracks may not be present until its too late. Evaluate snow and terrain carefully and steer clear of large loaded slopes that have no evidence of past avalanche activity (old piles of debris.) 

There is no hazard rating below 1,000’ due to a lack of snow. 

**Click HERE for the Summit Lake Summary posted Saturday.


 Show the Complete North American Avalanche Danger Scale
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.
0 NO RATING Below Treeline / Below 1,000'
Special Announcement

Merry Christmas and Happy Holidays from CNFAIC staff. Click HERE for a special holiday treat from our talented and lyrical interns. 


Avalanche Problem 1

Strong Easterly winds have been changing the surface conditions of our forecast zone over the last 4 days creating hard wind slabs on leeward features. Many ridgelines have been exposed down to rocks, dirt and old crusts. Observations yesterday found hard supportable wind slabs as low as 1600’ on Eddies. These slabs averaged around 5” thick and were failing in hand pits on old weak snow. Any wind slabs today will be hard and supportable (to a skiers weight) and may lure a skier well onto a slope before it fails. Be suspect of unsupported slopes steeper than 30 degrees that have a fat, smooth, pillow-type shape to them. Listen for that hollow, drum-like sound below your skis or use a pole to probe for that hard snow over weak set up.  These slabs could be as thick as 1-2’ deep in upper elevations and have the potential for initiating a much larger and more dangerous deep slab avalanche. More on this below. 

 

A handpit that failed on isolation on weak snow below, near surface facets and buried surface hoar. Yesterday at Eddies at 1900' on a West aspect. 

 

 

Many windward slopes have eroded down to rocks, dirt, and crusts, but cross loading is still possible around gullies and terrain features on windward slopes. Photo of the SE face of Seattle Rigdge near Pyramid Peak. 

 


Avalanche Problem 2

The recipe for deep slab avalanches has been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facetsObservations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart.

 

 

When dealing with a deep slab avalanche problem, keep in mind:

  • Large snow covered slopes that do not have piles of old debris under them are all suspect 
  • Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks   
  • It is possible to trigger this avalanche from below and it could run further than expected 
  • Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
  • Thicker areas (3-5+’ thick) will be difficult to trigger and several tracks may be on a slope before someone finds a trigger point

 

This Deep Slab avalanche on the NW face of Pastoral was remotely triggered from below on Dec.20 by a party of two skiers who were able to run out of the way of the debris. This is an example of the potential that still lingers in upper elevations, above 3000' on slopes that haven't avalanched. For more details on the snowpack structure click HERE and for a description of what happened click HERE


Mountain Weather

Yesterday Strong Easterly winds decreased to Moderate, averaging 15mph with gusts in the 30’s. Temperatures at lower elevations were above freezing, mid to low 30F’s at 1000’ and low 40F’s at sea level. Temperatures at ridge tops remained in the low 20F’s. An inch of new snow fell yesterday. 

Today a trace of snow is possible and winds are expected to be East, 5-20mph.  Skies could range from overcast to partly sunny. Temperatures in the lower elevations should start cooling into the 20F’s today. 

High pressure is expected to settle over mainland Alaska this week with several lows tracking South of the Gulf of Alaska. This should allow for some clear skies and cooler temperatures. Northerly gap winds are possible this week as well as an occasional snow shower.  

*Center Ridge SNOTEL is reporting erroneous temperature data. See Turnagain Pass DOT weather station for accurate temperature at 1000'

**A max gust of 72mph occured at 7am on 12/24/17 at Sunburst Wx Staion before winds decreased and gusts were averaging in the 30's mph most of the day. 
PRECIPITATION 24-hour data (6am - 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') *34  0.1  30 
Summit Lake (1400') 31  0.1  11
Alyeska Mid (1700') 31  0.2  27 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22  ENE  15  **72 
Seattle Ridge(2400') 26  ESE  15  48 

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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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