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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Thursday, December 24th 2015
Created: Dec 24th 6:01 am
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.
 Show the Complete North American Avalanche Danger Scale
Hidden Creek B&B LLC
Special Announcement

The Chugach National Forest has recently opened Johnson Pass trailheads (North and South) to motorized use.  Please see the "Riding Areas" table at the bottom of this page for current info on areas open to snowmachines.


The Bottom Line

A MODERATE avalanche danger exists above treeline and in the upper elevations of Turnagain Pass where triggering a slab 2-4’ thick is possible in steep terrain. The Southern side of Turnagain Pass and periphery areas (Johnson Pass, Lynx Creek, Summit Lake) are particularly suspect due to a shallower snowpack. This is a low probability but a high consequence situation and requires evaluating the snow and terrain carefully. Likely trigger spots will be in shallow areas near rocks and on unsupported convex rollovers. Choose terrain wisely, do not put multiple snowmachines or skier/riders on or under steep slopes all at once, and watch for shooting cracks and recent avalanches.

*Should today's winds exceed the forecasted 10-15mph be on the lookout for newly forming windslab and adjust to changing conditions.

Below treeline the danger is LOW where there has been less snow and less wind.   


Primary Concern

The weak snow that formed in early December sitting over the Thanksgiving Rain Crust or old hard snow is now buried under 2-4' of snow. This combination is our current cause for concern and heightened caution in the backcountry. Many large avalanches ran during the storm Saturday including a large D4 avalanche in Silvertip drainage

Yesterday several small skier triggered slab avalanches were reported near Pastoral above 3500’ on multiple aspects.  Two of these slabs may have been remotely triggered, a symptom of a persistent weak layer. No information is known about the weak layer/bed surface that caused these slides, but it is a good reminder that poor structure does exist within the top 2-4’ of the snowpack. This avalanche problem seems to be more reactive on the Southern side of Turnagain Pass and aligns with reports of snowmachine triggered slides in Johnson Pass and Lynx Creek two days ago.

Many people have been getting into steep terrain without issue, but these conditions warrant respect. Triggering a slab 2-4’ is possible in steep terrain and will be more likely in thinner areas near rocks and on unsupported convex features. Choose your terrain wisely and avoid slopes with high consequences. 

An avalanche that occured at the end of the Dec.19th storm had a long connected crown, just under 2 miles long on a ENE aspect of Twin Peaks ridge above Silvertip Creek. 


Secondary Concern

Multiple days of cold temperatures have been decomposing the top 8-10” of snow creating very weak surface snow. Yesterday a fast moving loose snow avalanche 'sluff' caused a skier to be knocked down and drug into an alder patch. Although it is unlikely that this avalanche problem will bury a person, it is capable of causing serious injury. The best way to manage a loose snow avalanche is by choosing terrain with low consequences and allowing the ‘sluff’ to pass by you while descending.

*Looking forward into the weekend a large storm is expected to arrive tomorrow morning and the current surface snow conditions (near surface facets and widespread surface hoar growth) will be a future layer of concern once burried.


Additional Concern

Yesterday 15-30mph Westerly gusts were recorded at various ridgetop weather stations and several groups observed drifting snow along ridgetops. Although this wind appeared to be short lived, it did move some snow around in the upper elevations.  Be on the lookout for the following:

Cornices: Recent wind loading can make cornices extra tender. A cornice fall (like the photo below) could be a big enough force to awaken a persistent slab. Give these features plenty of space and be careful not to accidently drive your snowmachine out onto them or have your ski lunch break in the wrong spot. 

Windslabs: Should you see snow being transported by winds, this is a obvious sign that wind slabs are forming on leeward features. Pay attention for stiff, pillowed, sculpted snow and look for shooting cracks. 

A fresh looking slab was reported yesterday in Superbowl between Magnum and Cornbiscuit. The exact trigger and timing are unknown, but appear to have been triggered by a cornice. If anyone has information about this recent slab/cornice failure please submit an observation HERE


Mountain Weather

Yesterday skies were clear and temperatures ranged from 5F to 15F. Westerly ridgetop winds averaged around 5-10mph and several gusts were recorded in 30’s mph on Seattle ridge. Overnight winds were light from the West and temps remained cold.

 

Today skies are expected to be clear and temps should stay in the teens F and start increases later in the day. Light Westerly winds will become Easterly and increase to moderate by the evening.

 

A Winter Storm Watch has been issued by the National Weather Service for Friday morning into Friday evening. Tomorrow heavy snow and moderate winds are expected on the Kenai Peninsula and could bring another 1-2’ of snow to the area. Temperatures are expected to warm up and the rain/snow line could reach as high as 1500’. 



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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 13F  51 
Summit Lake (1400') 7F  0 17 
Alyeska Mid (1700') 13F  36 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 9F  WNW  23 
Seattle Ridge(2400') 12F  WNW  35 

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: Mar 15, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: OpenSkookum drainage closes to motorized use on April 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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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