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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, February 1st 2018 4:42 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is MODERATE above 2,500' for triggering a slab avalanche 1-3' thick. Slopes with signs of wind loading will be the most suspect for triggering an avalanche. Additionally, watch for easily initiated loose snow avalanches (sluffs) on steep slopes.

Below 2500' the danger is LOW. Remember low danger doesn't mean no danger. 

 


 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
Special Announcement

Snug Harbor Road access to Lost Lake, Summit Lake, Palmer Creek and the Resurrection Pass Trail System all on the Seward Ranger District are open to motorized use as of today.

 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Because last week's storm loaded a widespread layer of surface hoar (a persistent weak layer) we are calling this a persistent slab issue and not just a wind slab. The main concern in the advisory area is finding a slope where the snow above the January 21st buried surface hoar is acting like a slab. We are not finding evidence of this below 2500'. Cold temperatures with the inversion have been quickly degrading the snow near and below treeline. Slopes near ridgelines in the Alpine, are where the winds over the weekend affected the snow and changed it from fluffy, low density powder to stiff and consolidated wind crust or slab. There were a couple reports of people intentionally triggering small slabs on wind-loaded slopes Tuesday that failed on the buried surface hoar, one skier triggered and one snowmachine triggered. These are a good reminder that despite the cold and clear weather now slowly faceting away the slabs; there is still the possibility of finding and triggering lingering slabs in leeward terrain today.  Remember that there is surface hoar is lurking underneath the recent snow and it's important to assess areas affected by wind. Slabs can be deeper in loaded areas. Pay attention to slopes where the snow feels stiff, looks pillowed or sounds hollow and watch for shooting cracks. A small slab in the wrong terrain could have high consequences. The easterly winds have picked up this morning blowing into the teens and 20s. Look for changing conditions today if you see snow getting moved around.

Evidence of a natural wind slab avalanche in Ragged Bowl and wind-affected snow. This was likely triggered during the higher winds around the Girdwood area Sunday into Monday morning. Photo: Mike Ausman

Snow pit from Cornbiscuit yesterday. The January 21st buried surface hoar was easy to find but not reactive in this spot. 

January 21st buried surface hoar preserved under the slab.


Avalanche Problem 2

Dry Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

As the cold weather continues to loosen and facet the surface snow, loose snow avalanches (sluffs) are becoming larger and faster by the day. Watch out for and manage your sluff in steep terrain features.

Natural loose snow avalanches and skier triggered sluffs on Magnum.

 


Additional Concern

Deep Persistent Slabs

Triggering a deep slab is becoming unlikely, but is still not out of the question above 3000'. In the high elevation snowpack there are a variety of weak layers in the mid pack and near the ground. Because of this poor structure, there is still a chance of triggering a deep slab if you find the wrong spot. The most likely trigger spots are in thin areas in the snow cover, often near rocks, or where the slope rolls over. 


Mountain Weather

Yesterday the clouds moved out and the skies became clear again. Temperatures were in the teens at upper elevations and single digits in the valleys. Winds were light and easterly. Overnight they picked up a little from the SE blowing in consistently in the teens. Temperatures dropped below 0F in the valley bottoms and were in the single digits to low teens at ridgelines stations.

Today will be clear and sunny. Temperatures will be in the single digits to teens with an inversion still in place. Winds will be easterly 5-15 mph gusting into the 20s. 

This sunny, cold weather is forecast to continue into the weekend. There is a chance of snow showers Monday afternoon and a "gradual uptick in temperature." Stay tuned to see what actually happens with the blocking high that is dominating our weather. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  18  0  0  62
Summit Lake (1400')  3  0  0  17
Alyeska Mid (1700')  11  0   0   51

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  12 NE  6 20 
Seattle Ridge(2400')  12 variable  7  18 

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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