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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, March 31st 2018 5:42 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger continues to be MODERATE above 1500’ in the periphery of the forecast zone, such as Girdwood Valley and South of Turnagain Pass. Triggering a hard slab avalanche 2-4 feet thick remains a possibility and may be triggered remotely. A generally LOW danger exists in the core zone of Turnagain Pass where triggering this type of avalanche is trending toward unlikely. Pay attention to afternoon warming and give cornices a wide berth. 

If daily warming and radiation break down a stout crust below 1000’ the danger could rise from LOW to MODERATE on Southerly aspects in the afternoon in this elevation band.  

If you are headed South of Turnagain Pass more snowpack info can be found in today’s Summit snowpack and avalanche summary 


 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

SKOOKUM VALLEY closes to motorized use tomorrow, Sunday April 1st, due to National Forest Plan. Boundary extends East of the Railroad tracks from Luebner Lake (South) to private property boundary (North). The rest of the Placer River Valley remains open. Click HERE for a map and more details.


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

It has been over two weeks since the last snowfall, 9 days since a strong wind event ended, and 8 days since the last human triggered avalanche. With little in the way of weather to contribute to avalanche danger the chances for triggering an avalanche are becoming unlikely. However if someone finds an unstable slope the size of the avalanche could be large and destructive. This scenario doesn’t fit neatly into the danger scale and we still recommend evaluating snow and terrain carefully and identifying features of concern.  Northern to Eastern aspects are the most suspect for harboring a generally thinner snowpack. This poor structure is the most pronounced in the periphery areas of Girdwood Valley and the South end of the Pass towards Johnson and Lynx Creek and Summit Lake. Terrain in the core Turnagain Pass zone is trending towards LOW danger, meaning triggering a slab avalanche is unlikely - but not out of the question. 

The slabs in questions are hard slabs 2-4' thick. The weak layers in question were formed in January and are various layers of facets and buried surface hoar. Stability tests this week have been trending towards good stability in the heart of our forecast zone. The one exception being Girdwood where observers experienced a large collapse on Thursday near Goat Mountain. Without any notable weather changes to tip the balance we remain in a low probability, high consequence situation where multiple tracks could be present on a slope before someone finds a trigger point and the slope releases. These trigger points are often in thinner areas of the snowpack near rocks or in scoured areas along ridges. Evaluate the terrain for consequences before committing to a slope and practice safe travel habits to minimize exposure in avalanche terrain. 

Sunshine:
If the sun shines in full force today be aware of warming later in the day on Southerly slopes. Especially steep southerly slopes with rocks that will help heat up the snow around them, aiding in possible wet avalanche activity. As we gear up for a weekend of sunny skies, keep the afternoon warming on your radar! Yesterday several ice climbers reported a stout crust breaking down and becoming unsupportable by 4pm in the afternoon on Southern aspects just below Treeline near Hope Wye.

Deep Persistent Slab is challenging to fit into the danger scale when stability is increasing due to their potential size and already low probability of triggering. 

 

A natural on a NE aspect of Frenchy Mountain, near the Hope Wye, was noticed yesterday and its unknown how recently this occurred.  Although this is just outside of our core advisory zone, it is a good example of a thin NE aspect that may still harbor unstable snow on the Southern end of Turngain Pass. 

 

Yesterday several groups of students in an avalanche class found poor structure on Pete's South, Magnum, and Eddies but did not get any notable failure in their stability tests. 


Additional Concern

Cornice

Cornices are large in many places. As we head into warmer, sunnier weather remember this can help de-stabilize them. As always, give cornices plenty of space and limit exposure underneath them.


Mountain Weather

Yesterday skis were clear and sunny most of the day. Daytime high temperatures near sea level reached the upper 30F’s and overnight dropped to low 20F’s.  Ridgetop temperatures were much cooler remaining in the teens to low 20F’s. Westerly ridge top winds were 5-10mph.  No precipitation recorded. 

Today clear and sunny weather is on tap. Daytime temperatures may reach the upper 30F’s near sea level and low 30F’s near ridge tops. Overnight lows will be in the low 20F’s to teens near ridge tops. Northwest winds may range from 5-15mph. No precipitation is expected. 

Tomorrow looks similar and clear skies are expected through Monday. Daily warming could increase into mid-30’s tomorrow afternoon in the upper elevations. Nighttime low temps are expected to drop into the low 20F’s again. Northwest ridge top winds may pick up to Moderate on Monday into Tuesday. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  28 76 
Summit Lake (1400') 24  31 
Alyeska Mid (1700')  28 71 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 16  15 
Seattle Ridge(2400') 22  NW  20 

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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