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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, February 10th 2018 5:37 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 is MODERATE above 1000’ where winds are adding stress to the snowpack. Triggering a shallow wind slab or a deeper slab 2’ thick is possible. Active wind loading, shooting cracks and ‘whumpfuing’ are obvious clues the snowpack is unstable.  Additionally in the alpine, above 3000’, the potential for triggering a deeper more dangerous avalanche exists on slopes with a shallow snowpack. The periphery areas like the Southern end of Turnagain Pass towards Summit Lake and portions of the Girdwood area are more suspect. 

Check out the Summit Lake 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

For all the Hatcher Pass users out there - Hatcher Pass Avalanche Center is having their annual fundraiser tonight, Saturday, Feb.10th, at the Palmer Moose Lodge!! HPAC is a growing avalanche center for a high use zone with a high number of avalanche accidents in Alaska. They need your support! Click HERE for details.


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
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Unlikely

Chance

Historic
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Size

Moderate to Strong Easterly ridgetop winds have been transporting snow and adding stress to the snowpack. Overnight Sunburst weather station recorded winds in 15-30mph range and Seattle Ridge was stronger, 20-40mph. Isolated pockets of newly formed wind slab may be easy to trigger, but more concerning will be drifting snow adding stress to a persistent slab and making the snow more cohesive. Several weak layers are buried within the top 1-2’ of the snowpack, including buried surface hoar and near surface facets. With our current snowpack structure these two avalanche problems (wind slab and persistent slab) are closely related. Basically they are both strong snow over weaker snow below. Slabs may range from small to large, soft or hard, and have the potential to break above you once committed to a steep slope. Identify smooth pillowed surfaces and evaluate the consequences of the terrain before committing to a slope. 

Easterly winds yesterday loading West facing slopes of Pyramid Peak. Winds can also cross load gullies and terrain features on all aspects.

 

 

January 21 buried surface hoar sits below 1-2' of snow and is widespread across our region. This is one of several persistent weak layers including near surface facets that may be lurking below wind drifted snow. 

 

 


Additional Concern

Deep Persistent Slabs

Weak snow can still be found near the ground and within deeper layers of the snowpack, above 3,000'. Although triggering a Deep Persistent Slab is less likely, it is worth keeping in mind that poor structure does exist in places with a generally thinner snowpack. Last Saturday (Feb.3) a large human triggered avalanche occurred on the East face of Twin Peaks and failed on weak snow (buried surface hoar and facets) sitting on a hard bed surface. This was a high consequence, hard to trigger avalanche where the 9th and10th skiers on a skin track found just the right trigger spot, a very shallow part of the snowpack. Luckily no one was caught or injured in this avalanche. A conservative approach would be to avoid large steep terrain with shallow snow cover or exposed rock. Wind scouring from overnight may be creating more trigger spots in thin snow covered areas.

The Twin Peaks avalanche was triggered at the apex of the crown in a shallow spot only 20" deep. 


Mountain Weather

Yesterday skis were clear with high clouds rolling in later in the evening. Ridge top winds at Seattle ridge were stronger than the rest of the area, but overnight winds increased at Sunburst weather station to 15-30mph. Seattle Ridge recorded several hours overnight with winds in the 30-40’s mph range.  An inversion kept some valley bottoms in the single digits and the alpine averaged in the low 20F’s. Radiation from the sun is starting to affect daily temperatures swings. No precip was recorded.   

Expect overcast skies today and Easterly ridge top winds in the 10-35mph range. Scattered snow showers are possible, but not much accumulation is expected. Temperatures may rise to the low 30F’s at sea level and mid to high 20F’s at higher elevations. 

Snow showers are possible Sunday, with a few inches of new snow forecasted. Another storm is tracking towards Southcentral, Alaska for Monday bringing warm temperatures and a possibility of more precipitation. At this point precipitation amounts are type (rain/snow) are uncertain. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 25  62 
Summit Lake (1400') 11  20 
Alyeska Mid (1700') 25  51 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  ENE  12  40 
Seattle Ridge(2400') 23  SE  22  49 

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

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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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