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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Tuesday, March 21st 2017
Created: Mar 21st 5:21 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

The avalanche danger is CONSIDERABLE in the Placer Valley and Portage Valley regions where up to 2 feet and more of snow fell on Sunday, March 19th. This new snow is sitting on a very weak base and human triggered slab avalanches 2-3' thick are likely on slopes 35 degrees and steeper. Warming afternoon temperatures could make natural avalanches possible again today. Cautious route finding and conservative decision-making are essential if you head to Placer Valley or find yourself in zones with over a foot of new snow.

In the Turnagain Pass zone, or any slope where around a foot or less of new snow fell, the avalanche danger is MODERATE. Shallow soft slab avalanches will be possible to trigger on slopes over 35 degrees. In all areas, expect sluffs on steep slopes, avoid travel on or under cornices and give glide cracks a wide berth. 

Summit Lake: Read the Saturday Summit Summary HERE.


Primary Concern

Ah, springtime in the mountains. Warm daytime temperatures, longer days (now longer than our friends in the lower 48) and a fresh dose of snow. What more could we ask for? Possibly, a more stable snowpack... Sunday's refresher storm that brought over 2 feet of snow to the Placer Valley and around a foot to Turnagain Pass and Girdwood fell on a very weak old surface of facets and surface hoar. In areas with greater snow amounts, triggering a slab avalanche is still very possible and even likely. Essentially, the places that are the most enticing for powder lovers (areas with up to 2 feet of new snow) will be the most likely places to trigger a large slab avalanche. In areas with lower snow amounts (a foot or less) triggering a smaller shallow slab is still possible.

There was a report of natural avalanche activity in the Placer Valley yesterday along with one snowmachine triggered slab avalanche. In the Turnagain Pass area, there was one report of a skier triggered avalanche on Magnum. Along with the avalanche activity, we had several reports of whumphing and shooting cracks. Interestingly enough, on our field day over on Seattle Ridge, we had a hard time finding unstable snow. The new snow here was quite shallow (10-12") and light - just not enough snow to overload the old weak snow surface.

For today, things to keep at the forefront of our minds:

  1. How much new snow is there where you are traveling?
  2. The more new snow the higher the likelihood of triggering a slab avalanche.
  3. Is the day heating up? Warming can increase the chance for triggering an avalanche.
  4. RED FLAGS? Recent avalanches, whumphing, shooting cracks? All these signs point to unstable snow.

Shallow soft slab avalanche triggered by a skier on Magnum in the Turnagain Pass area yesterday. Photo: Jordan Bancroft


Secondary Concern

Similar to the slab avalanche concerns above, expect the size of sluffs to be dependent upon the amount of new snow you find. That said, human triggered sluffs (loose snow avalanches) are likely in steeper terrain that were not affected by the sun yesterday. Natural damp or wet loose snow avalanches may still be possible with warming in the afternoon. Keep in mind, sluffs have the potential to initiate a slab lower on the slope

Dry loose avalanches on the West face of Eddies. Photo: Conrad Chapman 


Additional Concern

Persistent Slabs and Deep Slabs:  There are a variety of very old weak layers in our thin snowpack. The February 9th buried surface hoar sits 2-4+' below the surface and faceted snow sits in the mid and base of the pack. These weak layers (with varying degrees of strength) have been in a ‘dormant stage’.  Although unlikely, an avalanche breaking deeper in the pack isn't completely out of the question with the new snow load and warming temperatures. Areas such as Johnson Pass, Lynx Creek and on the Northern side of Girdwood Valley (near Crow Pass) are the most suspect and observers continue to find poor structure.


Mountain Weather

Partly cloudy skies covered the region yesterday. Intermittent light snow showers and cloud cover added a few flakes here and there but no measurable precipitation was recorded at the snow stations. During the past 24-hours ridgetop winds have been light (5-15mph) with moderate gusts (10-25mph) from the East. Temperatures that warmed during the day to 30F at 1,000' and 25F along ridgetops have dropped back down to the teens overnight. 

For today, we can expect another day of in-and-out cloud cover (partly cloudy skies) and no precipitation. Ridgetop winds should remain light 5-10mph from the East and Northeast with a possible bump to the 15-20mph range later this afternoon. Daytime warming will again let temperatures climb into the 25-30F range by the afternoon.

Looking ahead, mostly clear skies with warm days and cold nights is in our future. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 18  65 
Summit Lake (1400') 19  30 
Alyeska Mid (1700') 23  61 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 15  NE  24 
Seattle Ridge(2400') 20  SE  19 

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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