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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, January 4th 2018 5:16 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 is CONSIDERABLE on all aspects and elevations near 2,000' and above. Human triggered slab avalanches 1-2’ thick are likely where surface crusts are either thin or do not exist. Additionally, remote triggered avalanches from the side, below and from the top of slopes is possible. At elevations above 3,000’ there is still the possibility of triggering a very large slab avalanche that breaks in weak snow near the ground. Cautious route-finding and conservative decision-making are essential. Below 2,000’ the danger is MODERATE in avalanche paths where a slide occurring above may send debris.


 Show the Complete North American Avalanche Danger Scale
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

After several days of snowy weather, low visibility and a natural avalanche cycle, mostly clear skies are expected today. This will make travel above treeline inviting. If you are headed out in the backcountry please understand there are dragons lurking in the snowpack. Two dragons to be exact: 1) a layer of buried surface hoar sits 1-2' below the surface and is showing signs of being reactive, 2) weak snow near the ground exists at elevations above 3,000'. These issues are also being seen in the Summit Lake region.

The New Year's storm that began Dec 31st and ended yesterday, Jan 3rd, added 1-2' of snow in most areas, possibly more at the higher elevations. This snow fell on a layer of surface hoar and near surface facets, creating a persistent slab problem. Rain fell up to 2,300' at one point during the storm, which has formed crusts in the top foot of the snow at elevations below 2,000'. Above ~2,000' where moist to dry snow exists without crusts are where triggering an avalanche is most likely. Things to keep in mind:

1-  Human triggered avalanches 1-2' thick are most likely above 2,000'
2-  Remote triggering from the top, side or bottom of a slope is also likely
3-  Avalanche size is expected to be large enough to bury and kill a person 
4-  The larger the slope the larger the avalanche

Performing quick pits to assess the bonding of the New Year's snow to the weak snow below is a great idea, but not something to completely hang your hat on. The buried surface hoar may have been blown down in your pit, yet remains lurking on the slope you plan to ride. Today and tomorrow are days to be extra cautious as there are too many signs pointing to an unstable snowpack. Along with the buried surface hoar problem, wind slabs and cornice falls are possible along ridgelines. One of these avalanches can trigger a larger avalanche below. 

Check out these videos. The first is the general snowpack set-up, the second is a close up/snow motion video of the collapse and propagation of the buried surface hoar found yesterday on Sunburst: 

 

  

 


Runnels from the rain exists around 1,600'. At these lower elevations the wet snow is freezing into a crust and triggering an avalanche is unlikely.


Avalanche Problem 2

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

In the Alpine, above 3,000’, weak sugary snow (basal facets) sits near the ground. The storms over the past few days have added additional load to slopes that already have a hard slab 3-5+ feet thick. At these elevations, human triggered, large and dangerous deep slab avalanches ARE still possible. This is a high consequence avalanche problem that is impossible to outsmart and can take a long time to heal. Keep this in mind as improving visibility in the next few days may allow for travel to the Alpine. It is really important to remember that triggering an avalanche in the upper layers of the snowpack may then initiate a deep slab avalanche. Cautious route-finding is essential. This includes thinking about the remote trigger potential from below. 


Mountain Weather

Obscured skies and light snow showers filled the area yesterday. Snowfall yesterday at the mid elevations accumulated to 2-3" at most locations with .2-.3" of water equivalent. An additional couple inches is likely to have fallen in the upper elevations. Winds turned Westerly yesterday and were light in the 5-10mph range during the past 24-hours. Temperatures have dropped overnight with clearing skies and are sitting in the mid-20's at 1,000' and near 20F on ridgetops.

Today, mostly clear skies are forecast with valley fog to be expected. Ridgetop winds will be Westerly in the 5-10mph range. Temperatures will continue to decrease to the teens along ridgelines and the mid 20'sF at 1,000' as cold air streams in with the winds.

Another clear sky day is on tap for tomorrow before a round of snow (and it looks like snow to sea level) moves in on Saturday - stay tuned!

*Seattle Ridge anemometer is rimed. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  0.2  46 
Summit Lake (1400') 28  0.3  16 
Alyeska Mid (1700') 30  0.3  39 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22   21
Seattle Ridge(2400') 25  *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: 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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