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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Friday, December 26th 2014
Created: Dec 26th 5:21 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
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The Bottom Line

There is a MODERATE avalanche danger on all aspects above 2,500'. The possibility remains for a person, or group of people, to trigger a large and dangerous slab avalanche that breaks 2-3' deep on a layer of buried surface hoar within the snowpack. This is a low probability but a high consequence situation and results in a tricky snowpack that cannot yet be trusted.

An additional avalanche concern today will be more obvious - wind slab avalanches. Wind slabs 6-12" thick are likely to be found and possible to trigger at and above treeline due to the strong winds throughout our region yesterday.

A generally LOW danger exits below treeline where winds did not affect the surface snow. However, it is important to keep in mind what you are traveling under and watching for other parties that may be above you. 


Primary Concern

Although new snow has been slowly trickling into the region (2-4" yesterday), our primary concern still lies with the fact we have a persistent weak layer buried in our snowpack. If you have been following our forecast for over a week now, you are well aware of this layer and its potential to create large avalanches. The culprit is buried surface hoar and is well documented on our observations page. The slab that sits on top is anywhere from 1-3' thick and is composed of dense settled snow. Adding to the load is the 8-12" of new snow that has been blown into drifts and slabs over the past week.

This weak layer and slab combination is present from around 2,500' to the ridgetops. With each day that goes by, the weak layer continues to adjust to the slab and triggering an avalanche becomes less and less likely. But, the catch is, the consequences remain high. If a person (or more likely a group of people) collapse the weak layer a resulting avalanche may propagate across an entire slope and potentially around terrain features into another slope. This is a tricky situation and some things to keep in mind are:

- Obvious signs of instability (cracking or collapsing) are likely not to be present until it is too late.
- Likely trigger points are thin spots in the slab. For example, steep rollovers, rocky areas and thinner snowpack zones such as the south end of Turnagain Pass.

For a safe day in the backcountry this holiday season, we are recommending to continue to keep slope angles below 35 degrees with nothing steeper above you. If choosing to venture onto steep slopes, very careful snowpack assessment is necessary as well as remembering your safe travel protocol:
 - Only expose one person at a time
 - Have an escape route planned
 - Make sure your partners are watching closely
 - If an avalanche is triggered, do you know how to use your rescue gear and perform companion-rescue?

*Remember, this type of avalanche problem can result in a large avalanche that can cause traumatic injury as well as burial.


Secondary Concern

Wind was unfortunately the Christmas word of the day in the Kenai mountains! Sustained winds blew for most of the afternoon gusting as high as 65 mph on Sunburst. This combined with the soft snow that has accumulated throughout the week has formed wind slabs near and above treeline. Snow was rapidly being moved around yesterday. Flagging off the top of the peaks, tracks filling in and small slabs at treeline were observed. Be on the lookout for evidence of windloading and avoid steep lee and crossloaded slopes as well as corniced ridgelines. While traveling, look for pockets of wind drifted snow around terrain features, rounded pillows, chalky or hard snow. Also, watch for shooting cracks as seen in the photo below, these are a red flag that a wind slab is present.  Any snow left to transport may continue to be moved and deposited with the forecasted moderate winds today. 

Shooting cracks in a wind slab from Christmas Day - Summit Lake area.

 


Mountain Weather

During the past 24-hours the mountains have seen 2-4" of new low density snow with strong Southerly winds (see detailed table below). The rain/snow line hovered around 500' with precipitation shutting off around 1pm. Temperatures that were in the mid 30's F at sea level and the mid 20's F on ridgetops, have decreased a few degrees overnight with mostly clear skies.

Today, we are in store for partly clear skies with a snow shower or two moving through - adding a trace of snow at best. Ridgetop winds, which shifted to a Westerly direction overnight, will continue in the moderate category (10-20mph) through the day from the West. Temperatures look to rise to around 30F at 1000' and the mid 20's F on ridgetops. 

Coming into the weekend, skies should remain mostly clear tomorrow with moderate, to strong at times, Westerly to Northerly winds. Sunday, things begin to change dramatically. A large scale low pressure system far to our south moves north that will usher in a strong and warm southerly flow. This flow will bring warm temperatures to our region with precipitation in the form of rain (yes, again) up to elevations as high as 2000'. Cross your fingers enough cold air is in place to keep the rain/snow line low!

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29  0.3  30 
Summit Lake (1400') 28  0.2 
Alyeska Mid (1700') 30  2"   .21 25.5 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  SW  18  65 
Seattle Ridge(2400') 24  15  40 

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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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