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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Friday, April 3rd 2015
Created: Apr 3rd 5:34 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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'
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Special Announcement

Our new observations page is up and running and its easy to use on an iphone. Observations from the field are the backbone of the advisory and help us to provide the most accurate information possible.  Any info is welcome and it doesn't need to be perfect!  Thanks to everyone that has submitted so far this season.


The Bottom Line

The avalanche danger in the Alpine will increase to CONSIDERABLE today as sunny daytime temperatures climb into the 40’s F. On shaded slopes above 2500’ an already unstable snowpack exists and a slab 2-3’ thick if triggered will have high consequences. On Sunny aspects as hot daytime temperatures saturate the snowpack triggering a wet avalanche is possible as the snow becomes moist. Today it will be important to avoid steep shaded aspects, as well as steep sun exposed slopes later in the day.

Below 2500’ the avalanche danger is LOW, but on sunny aspects (South and East facing slopes) the snowpack could become saturated enough to produce wet loose avalanches on steep features. 

Over the last few days several large skier triggered slab avalanches have occurred on Northern and Western aspects including this avalanche on “Basketball Chute,” a Northern aspect of Magnum.


Primary Concern

Today very warm daytime temperatures will be contributing stress to an already stressed weak layer that is sitting below a 2-3’ slab on Northern and Western aspects.

Over the last three days several skier triggered slab avalanches have confirmed this problem being widespread throughout Turnagain Pass on shaded slopes above 2500’. Yesterday we investigated a large skier triggered slab avalanche on a Northern aspect of Magnum that happened on April 1st. The slab depth was 2-3’ deep and it ran a total distance of 1300’ to the valley floor. The skier went for a 1000’ ride, but was not buried or injured. We could not access the crown, but dug a pit on a similar aspect and elevation and found several layers of weak faceted snow and crusts beneath a 2.5’ slab.

Obvious signs of instability like collapsing may not be present in the heart of our forecast zone (Tincan, Sunburst, Magnum) and assessing the snowpack on Northern slopes will be difficult to do safely. If an avalanche is triggered today the consequences will likely be high. It will be important to avoid steep Northern and Western aspects above 2500’ until the weak layer(s) have more time to adjust to the load. 

Yesterday a group of skiers on Seattle Ridge felt a collapse and found a large avalanche in Main Bowl in a similar area they had just skinned through. (photo below) It is possible that they triggered it remotely from the Ridge, but it was unwitnessed. It occured between Noon and 1pm as temperature were suddenly rising. This event points to greater instability in this portion of the forecast zone. Photo by John Fitzgerald.


Secondary Concern

Over the last three days daytime temperatures have been rapidly increasing around 12pm and today’s hot sunny weather will likely see a similar spike. Springtime conditions exist on predominantly sunny slopes where the snow pack is likely to become saturated throughout the day on Southern and Eastern aspects. If daytime temperature climb into the mid 40’s to 50’s F as forecasted, wet loose and wet slab avalanches will be a concern at all elevations holding snow. 


Additional Concern

Cornices have grown very large over the last few weeks and with todays warm temperatures natural cornice fall is possible. If traveling along a ridge give cornices a lot of space– they can break farther back than you think.  Adjust your route if you find yourself traveling below a cornice. In the right place (like Seattle Ridge area) a cornice fall could trigger a large slab avalanche. 


Mountain Weather

Yesterday skies were overcast and in the afternoon and became partly cloudy. Temperatures were very warm, 30-40’s F at mid elevations. Along ridgetops temperatures reached the low 30’s F and winds were light from the Northeast.

Overnight temperatures dipped below freezing along ridgetops, but at mid elevations stayed in the low 30’s F.  Ridgetop winds shifted from the Northeast to the West, but remained light (5-10mph.) An inch of new snow was recorded at Center Ridge Weather Station.

Today very warm and sunny weather is expected.  Daytime temperatures will be warm, 30F - 40F. Near sea level temperature could reach the 50’s F during the warmest part of the day. Winds are expected to be 5-15mph from the North along ridgetops and no precipitation is expected. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 36  .01  60 
Summit Lake (1400') 35  10 
Alyeska Mid (1700') 35  33 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 27  Var.  20 
Seattle Ridge(2400') 30  Var.  11 

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.


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