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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   CNFAIC Staff  
Monday, December 22nd 2014
Created: Dec 22nd 5:37 am
3 Considerable Alpine Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Treeline Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
0 NO RATING Below Treeline
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Special Announcement

Happy Solstice! Today we will gain 6 seconds of daylight. We’re celebrating every second we can get.


The Bottom Line

Today the avalanche danger above treeline remains at CONSIDERABLE. Human triggered slab avalanches 1-3+’ deep are likely in steep terrain above 2500’. These have the potential to propagate across entire slopes. An avalanche of this size could have very high consequences. You will be more likely to trigger an avalanche in areas where the snowpack is thin or on features like steep rollovers or near rocks. Conservative decision-making and careful snowpack evaluation is essential today if choosing to venture onto steep slopes. 

The avalanche danger at treeline (2000 – 2500’) is MODERATE. The likelihood of human triggered avalanches is possible at this elevation, but it’s more likely that an avalanche triggered above could run into this zone. Identify steep slopes above and practice safe travel techniques.  


Primary Concern

A short burst of snowfall yesterday morning added a welcome 5-9" of very low density snow in the Girdwood Valley and 1-4" at Turnagain Pass. With the chance for a few more inches of light snow today, this will add to the soft surface conditions, but the avalanche concerns will remain deeper in the pack.

The primary concern continues to be a slab (1 – 3+’ deep) sitting on a layer of intact buried surface hoar. Last week this combination (slab + weak layer) was very touchy causing several large human triggered avalanches including a full burial in Turnagain Pass. As this layer has had time to adjust we have noticed it gaining strength and getting harder to trigger in our test pits. Check out this VIDEO from yesterday. Unfortunately, when it does collapse there is a lot of potential to propagate over an entire slope. In other words, the probability of triggering a large avalanche is decreasing, but due to its thickness and potential to propagate, the consequences are high.

In the right type of terrain you might trigger an avalanche or you might not. Many people could ski the same steep slope before someone hits the right trigger spot. It can be nearly impossible to know the exact location of these areas, but a good rule of thumb is to avoid thin snowpack areas, steep convex rollovers and areas near rocks. If you find yourself creeping into steeper terrain be aware of the consequences below you. It can be easy to assume that just because a slope has been skied it is deemed “safe.” 

There is a lot of uncertainty around this avalanche problem. We haven’t received any reports of recent avalanche activity in the last few days. Our observations have been limited to our roadside access on low consequence terrain of Tincan, Sunburst, and Seattle Ridge.  We have only been able to investigate this slab plus weak layer combination on slopes below 35° in Turnagain Pass. We don’t know how reactive this weak layer is south of Sunburst or in elevations higher than 3400’. Girdwood received the highest amount of precipitation from the Dec.14-17th storm and this slab layer gets gradually thinner as you head south through Turnagain Arm. We know that the Summit Lake area has the shallowest snowpack, and we suspect it could be easier to trigger a persistent slab in this region. 

 


Mountain Weather

Yesterday morning Turnagain Pass received 1-4” of low-density snow and 5-9” fell in the Girdwood Valley. Winds were light from the East with temperatures in the mid to high 20’s F. 

Overnight there has been no new precipitation recorded. Winds were calm and temperatures have increased to 32°F at sea level and the mid 20's F on the ridgetops.

There is a chance we could see up to 4-6” of low density snow at higher elevations today with very light and variable wind. This may be in the form of rain at sea level as temps are supposed to stay in low 30’s F.

Over the next few days, showery conditions are expected in the Western Prince William Sound area and could bring short bursts of snow to Girdwood and Turnagain Arm. Unfortunately, the forecast has a lot uncertainty and these small bands of moisture could miss us. Temperatures are expected to remain in the high 20’s F to low 30’s F at 1,000' with light and variable ridgetop winds. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  0.1 28 
Summit Lake (1400') 28   0
Alyeska Mid (1700') 31  0.43  21

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 25  20 
Seattle Ridge(2400') 27   ]N/A N/A  N/A 

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: Dec 20, 2014 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedWe are still lacking sufficent snow at highway elevations. Continue to check back here for the latest info on motorized openings on the Chugach National Forest.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: Closed
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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
© 2014 Chugach National Forest Avalanche Information Center. All rights reserved.
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