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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, March 20th 2018 4:29 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 CONSIDERABLE above 2500'. Strong winds today could trigger natural wind slabs in the Alpine. Triggering a large, destructive slab avalanche 2-4+ feet thick is possible on all aspects above 1000'. Watch for tender wind slabs along ridgelines and avoid cornices. Pay attention to afternoon warming. Evaluate snow and terrain carefully. 

Below 1000' the danger is LOW. Wet snow is now freezing into hard crusts. 

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
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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 yesterday morning and the road remains closed, the most recent information is available on the HPAC facebook page. Check out the ADN article HERE. Significant avalanche activity has occurred over the past week region-wide from Hatcher Pass all the way South to Lost Lake near Seward

 


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday's weather was all over the place. Snow and rain in the morning and then sunshine, strong winds and cooler air moving into the region. There were a few dry loose avalanches and small wind slabs observed. Today continued wind loading may trigger natural wind slabs and/or add stress to the snowpack. It is also important to keep in mind that triggering a deep slab avalanche 2-4+ feet thick remains possible. On Saturday snowmachiner triggered slab in Main Bowl of Seattle Ridge, the slope had tracks on it from the day before and was remotely triggered from below. Remember that over the past week many large human triggered avalanches and/or natural avalanches have released from Girdwood to Lost Lake. Some of these avalanches have been remotely triggered and some with skier/snowmachiners on the slope.  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. 

*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. 

Avalanche triggered on Sunburst last week illustrates the trigger point that had a shallower snowpack near a rocky ridge. 

Deep slab structure: 3 feet of snow over a buried weak layer.

 


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Strong Northwest winds blew 25-35 mph yesterday and gusted into the 70s on Seattle Ridge. Winds are forecast to remain elevated today and ramp up even more this evening into tomorrow. Be aware of 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 fresh wind slab could step down to older snow in the snowpack and create a much deeper and more dangerous avalanche. 

Wind loading yesterday. 


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 started out with snow and a little rain (at lower elevations) and then the wind started to blow from the Northwest. The skies cleared and the sun came out. Temperatures were in the mid 20Fs to mid 30Fs. The NW winds were blowing 25-35 mph with gusts into the 70s. Overnight temperatures dropped into the low 30Fs and low 20Fs/high teens. Winds continued from the NW gusting into the 30s and 40s. 

Today will be partly cloudy with slight chance of snow showers. Winds will remain elevated from the NW gusting into 50s. Temperatures will be in the 20Fs to low 30Fs. Tonight skies will be clear and temperatures drop into the teens and single digits. The NW winds continue gusting into the 40s. 

Wednesday is forecast to be clear and sunny. The winds may be even stronger.  High pressure continues until the weekend and then there looks to be shift back to an active weather pattern. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  30  2 0.2   83
Summit Lake (1400')   25   2 0.1  33
Alyeska Mid (1700')  28  3 0.28   78

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  17 NW  10  47 
Seattle Ridge(2400')  24  WNW  30  70 

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: Apr 20, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: Open
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: Open
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: Open
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.


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