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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, January 11th 2019 7:00 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

A generally LOW avalanche danger exists across all elevations bands for the Turnagain area. Low danger does not mean no danger. Watch for wind affected snow where an isolated wind slab may release on a steep terrain feature. Glide cracks are creeping open and may avalanche without warning. Limiting/avoiding exposure under them is prudent. Give cornices a wide berth and watch your sluff.

SUMMIT LAKE / JOHNSON PASS / LYNX DRAINAGE: Keep in mind buried weak layers exist in the middle and base of the snowpack. More potential for triggering a large slab avalanche exists in this zone. Choose terrain wisely and please read the Additional Concerns below. 


 Show the Complete North American Avalanche Danger Scale
1 Low Alpine / Above 2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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

Check out our calendar for upcoming avalanche classes and events in January! Lots of opportunities with all the avalanche education providers in the area.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday a group found ‘touchy wind slabs’ on a Southeast aspect of Seattle Ridge near Bertha Creek Campground. These hard slabs were 3-10” thick, and formed on top of loose faceted snow and surface hoar that hundreds of people have been skiing and riding on this week. Moderate Northwest winds have channeled through some terrain in our forecast zone, but not all. Many folks have continued to get into steep terrain without incident  where snow conditions remain generally stable. These reactive wind slabs are an example of unstable snow that can be found on some terrain features. Today will be the last sunny day before a big weather pattern shift. If you’re headed into the mountains identify wind-affected snow that looks smooth or pillowed. Hard supportable snow that sounds drum-like should be suspect and could allow a person onto it before a slab releases.

Practice safe travel habits, such as exposing one person at a time, watching your partners and grouping up in safe zones. These are key ways to minimize risk. Ease into steep terrain and factor in the consequences should you encounter a wind slab or one of the following:

  • Glide avalanche:  
    • Identify glide cracks and avoid spending any time under these features. Glide cracks are opening and have avalanched within the last week. Glides are completely unpredictable and not human triggered.
  • Persistent Slab avalanche: 
    • Triggering a slab deeper in the snowpack is unlikely, but not out of the question in complex terrain. A layer of buried surface hoar 1-3' below the surface has been mostly unreactive or hasn’t been found in most test pits over the last week.
  • Cornice fall: 
    • Remember cornices often break farther back from ridges than expected. Give them a wide berth.
  • Loose Snow Sluffs:
    • Be aware of fast moving surface snow in steep terrain. Sluffs are slowly becoming larger as the cold weather weakens surface layers.

Looking South from Center Ridge yesterday. The terrain in the Sun, SE shoulder of Seattle Ridge remains suspect for reactive wind slabs. This is a common area affected by NW wind direction. 

 

Loose snow surface conditions and glide cracks on a SW aspect of Sunburst yesterday. Close up of surface hoar, a possible weak layer lurking under isolated wind slabs. Photos by Kyle Van Peursem


Additional Concern

Persistent Slabs

South of Turnagain - Lynx Creek/Johnson Pass/Summit Lake zone:  A poor snowpack structure exists in these areas. The buried surface hoar that we have been talking about over the past week has been found as well as facet/crust combinations in the bottom of the snowpack. The last avalanche cycle was during the New Year's storm, and overloaded a variety of these weak layers in Summit Lake. Cold weather this weak has been helping stability around the area, but localized NW winds this week may have added additional stress. Steep slopes without old debris below remain suspect. If you're headed this way, the snowpack becomes more complex - evaluate terrain exposure and the snowpack as you travel.


Mountain Weather

Yesterday: Skies were clear and sunny and temperatures in the alpine dropped to around zero F. Temperatures in the mid elevations remained in the single digits, but some areas like Portage Valley were closer to -10F. Ridgetop winds were light from the Northwest, 5-15mph. No precipitation occurred.

Today: Expect similar conditions, mostly sunny skies and sub zero F temperatures. Ridgetop winds are expected to remain light, but will shift from a SW direction to an Easterly direction in the evening. Cloud cover is also expected to move across our region this evening along with rising temperatures in anticipation of a pattern shift. Light snow showers are possible overnight.

Tomorrow: Low Pressure will be pushing the cold arctic air north as a series of storms track into our region. Temperatures will continue to rise through the weekend to above freezing temps in the lower elevations by Sunday. Easterly winds will build early Saturday morning and intensify by the evening. Expect precipitation to start out as snow, but rain is likely overnight in the lower elevations.

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 53 
Summit Lake (1400') -4  22 
Alyeska Mid (1700') 41 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 19 
Seattle Ridge(2400') *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, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Closed

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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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