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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, February 19th 2018 6:08 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger remains MODERATE above 1,000' on all aspects. Human triggered slab avalanches 1-2' thick, and potentially larger, remain possible. These are either shallow old wind slabs or larger slabs that break in weak layers deeper in the snowpack. Sunshine may warm southerly slopes today and could contribute to instability on these aspects.

The Summit Lake area has seen more avalanche activity over the past week. Take a look at the Summit Summary HERE. 


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


Hatcher Pass users: 
Dangerous avalanche conditions exist in this area. Several close calls have occurred over the past few days. Please see the Hatcher Pass Avalanche Center forecast before heading that way. 


Avalanche Problem 1

Persistent Slabs

Almost Certain
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Unlikely

Chance

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Persistent Slabs:  Despite the mostly quiet weather and lack of people triggering avalanches over the past week, triggering a slab avalanche up to 2' or more remains our main concern for President's Day. These slabs are becoming more difficult to trigger with time, but a large and unmanageable slide is still possible. Between 1 and 2' below the surface is the Jan 21 layer of buried surface hoar with weak facets directly below. This layer continues to show signs of reactivity. Red flags may not be present before a slope releases and snow pits can be misleading. Simply the knowledge there are weak layers below your feet or snowmachine should not be forgotten. Add sunshine and calm winds in the forecast today, and that 'likelihood of triggering' could increase slightly - both from increased traffic (triggers) and from sunshine affecting Southerly facing slabs. The most likely place to find these are slopes that have not seen significant traffic this season. 

Sunshine:  It's that time of year when we need to pay attention to the sun. On calm days the sun can heat up Southerly aspects enough to melt surface snow. This heating can also cause a slab sitting on a weak layer to become more reactive. Keep this in mind if you are enjoying Southerly aspects later in the day. 

Wind Slabs:  Watch for old wind slabs that could pop out from you on steep slopes. Steep rocky terrain where the slab is not supported from below are the most suspect. In general, most wind slabs are fairly well locked into place.

Cornices:  Don't forget about giving cornices wide berth at all times. Also, sunshine can be a big factor in de-stabilizing these during the afternoon/evening hours.

Old lingering wind slabs and cornices may become easier to trigger/fail with daytime warming and direct sun. Image from Warm-up Bowl on Seattle Ridge, Saturday, 2/17.

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Additional Concern

Deep Persistent Slabs

As you plan your day, keep in mind that there are deeper persistent layers that could 'wake up' if you find the right spot above 3,000' in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass and the Summit Lake area. 


Mountain Weather

Overcast skies with light snow flurries were over the region yesterday. Most areas only picked up a trace of new snow, but a couple inches may be found at upper elevations. Ridgetop winds were generally light with moderate gusts from a Southerly direction (5-15mph) during the day and have decreased to light and variable overnight. Temperatures dropped from 30F to the upper teens along ridgetops late in the day yesterday. Valley bottoms have remained warm, in the 20'sF, with cloud cover limiting a nocturnal inversion.

For today, President's Day, skies should clear this morning and a mostly sunny day is expected. Ridgetop winds look to remain light from the Northwest. Temperatures should warm to the upper 20'sF along ridgetops with daytime heating and valley bottoms to around 30F. 

Tomorrow, and through the mid-week, partly cloudy skies are forecast with the possibility for Westerly winds to increase on Wednesday before a chance for snow on Thursday. Stay tuned.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  trace  63 
Summit Lake (1400') 26  trace  25 
Alyeska Mid (1700') 27  trace  0.01  56 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22  variable  One gust to 37 
Seattle Ridge(2400') 25  ESE  12  27 

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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