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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, March 21st 2018 4:47 am by Aleph Johnston-Bloom
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'. Triggering a large, destructive slab avalanche 2-4+ feet thick is possible on all aspects above 1000' and may be remotely triggered. Watch for wind slabs along ridgelines and avoid cornices. Pay attention to afternoon warming. Evaluate snow and terrain carefully. 

Below 1000' the danger is LOW.  

Check out the most recent Summit snowpack and avalanche summary if you are headed South of Turnagain Pass.

 


 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

An avalanche crossed the Hatcher Pass road Monday morning and the road remains closed as of this morning. A Professional observation from Hatcher Pass Avalanche Center is available HERE.  Read the ADN article HERE. Check out our observations page for information about the avalanche activity that has occurred over the past week region-wide, from Hatcher Pass all the way South to Lost Lake near Seward HERE. 

 

 


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

A large avalanche was remotely triggered by a helicopter landing at a pick-up spot in Winner Creek near Girdwood yesterday. This avalanche occured at 2500' and released on the layer of weak faceted snow on a slick crust that has been the culprit in most of the avalanches over the past week. It was triggered from 1/4 of a mile away, wrapped 750' around a ridge releasing on multiple aspects and the crown was 3-6' deep. The pick-up spot had been used 10 times the day before. Why did it go the 11th time? The likelihood of natural avalanches has decreased as winds have hammered many areas and stripped away all the soft snow but a skier or snowmachiner triggering an deep slab avalanche remains a very real and scary possibility. Knowing where in the terrain that avalanche could be triggered and what it will take to trigger it is the hard part. This is the unfortunate reality of this type of avalanche problem. With a deep slab problem it is important to remember no signs of instability may be present before a slope releases. It may be the 10th person onto the slope that finds the trigger point and slopes may be triggered remotely. It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point. Widespread buried surface hoar and facets have been well documented at all elevations under a thick, connected slab and finding the wrong spot could be deadly.  

Crown in Winner Creek, avalanche wrapped around the ridge to the north.

 

Arrows point to crowns on both sides of the ridge

Snowpack structure on Tincan. Weak snow under a hard slab

 

 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The Northwest winds continued for a second day yesterday blowing 25-35 mph and gusting into the 60s on Seattle Ridge. Winds are forecast to remain elevated today into tonight and then mellow out by tomorrow. Most of the soft snow is now either blown into the atmosphere or been pounded into hard slabs and sastrugi. However, while traveling along ridgelines, be aware of the potential for wind slabs on a variety of aspects due to unusual wind loading patterns and cross loading. Smooth supportable surfaces where the snow is hollow sounding are suspect, especially if the slope is unsupported. Look for cracking and identify terrain features with a pillow-shaped look where triggering a wind slab could break above you. A wind slab could step down to older snow in the snowpack and create a much deeper and more dangerous avalanche.

Seattle Ridge has been getting top-loaded by this wind direction. 


Additional Concern

Cornice

Cornices are large and looming and wind loading can add stress. Give these an extra wide berth and limit exposure underneath them.  A cornice fall could trigger an avalanche on a slope below.


Mountain Weather

Yesterday was partly cloudy with temperatures in the teens at upper elevations and low 30Fs at sea level. Winds continued from the NW building mid day blowing 20-35 mph and gusting into the 60s. Overnight skies were clear, temperatures were in the teens to mid 20s and winds remained strong. 

Today is forecast to be sunny and clear with temperatures in the teens again at upper elevations and 20Fs to low 30Fs at lower elevations. Winds will be from the NW 15-30 mph gusting into the 40s and 50s. Temperatures overnight will be in the teens and single digits and winds are forecast to die down by the next morning. 

Thursday and Friday look to be clear, sunny and calm. The next weather system moves in over the weekend and the pattern looks active into mid-week. Stay tuned for details. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  24  0  82
Summit Lake (1400')   27    0   0    32
Alyeska Mid (1700')  24   0   0    77

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  15  NW  13 41 
Seattle Ridge(2400')  22  NW   35 67 

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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