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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Thursday, April 9th 2015
Created: Apr 9th 5:53 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
0 NO RATING Below Treeline / Below 1,000'
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Alaska Mountaineering and Hiking
The Bottom Line

The avalanche danger in the Alpine will be CONSIDERABLE today as strong winds and new snow are expected to cause storm snow instabilities and add stress to the snowpack. Triggering a slab up to 12” thick will be possible in the upper alpine and if the sun should make an appearance later in the day, natural wet loose avalanches are likely. It is possible that this new snow load could activate older layers and triggering a slab 2-3’ thick will be a concern on steep large slopes. Careful snowpack evaluation and conservative route-finding will be essential today.

Below 2500’ the avalanche danger is MODERATE where triggering a storm slab up to 8” thick will be possible, but unlikely to bury a person. 


Primary Concern

Another storm has arrived this morning and 6-10” of new snow is expected in the upper alpine in Turnagain Pass. Ridgetop winds have been averaging in the 40s mph with a recent gust to 80 mph from the East Northeast at Sunburst Weather Station. As of this morning several inches of wet heavy snow have fallen along the roadside in Turnagain Pass, and 4" has been recored at the midway station at Alyeska. Today’s forecast is calling for .7” of water at higher elevations with an additional .3” of water this evening. Rain/snow line will likely move from 500’ to 1500’ as temperatures increase throughout the day.  

This is the second storm to hit Turnagain Pass and Girdwood in the last 48hours. On March 7th a quick hitting storm brought gale force winds (averaging 40s mph) and dumping 12” of new snow in the upper Alpine of Turnagain Pass and 26” at Alyeska. Today’s storm looks similar with slightly less precipitation expected.

 

WIND SLABS and STORM SLABS

If strong winds and precipitation amounts reach their potential, wind slabs 10-12” thick could be easily triggered on steep leeward features along ridgetops. At lower elevations protected from winds fresh storm slabs up to 8” thick could be found in steep terrain. On Southern and Eastern aspects triggering a deeper pocket (up to 2’ thick) may be possible where an existing 12” of settled snow is sitting on a sun crust. Today it will be important to let this new storm snow adjust before venturing into bigger terrain. If the sun makes an appearance this afternoon, solar radiation will make slabs more tender and easier to trigger.

A small (D1.5) storm slab was visibile yesterday on Tincan's Common bowl. This was triggered near the end of the March 7th storm and is an example of storm slab hazard.

 

 LOOSE SNOW AVALANCHES

Sluffs will likely be a minor concern today, but if the sun appears wet and dry loose avalanches will likely be fast moving and could pick up speed and volume given a large enough slope.

 

CORNICES

Today’s strong winds and new snow will be adding stress to very large cornices. Natural cornice fall is possible today and thus will be important features to avoid. 

 

Conservative decision making is essential today and If the visibility improves this afternoonn resisting temptation will be key. it will be important to give large open slopes time to adjust even if obvious signs of instabilty are not present. Don't forget this is the second new load of snow to fall in the last 48 hours.  

 


Secondary Concern

North facing aspects above 2,000' have a variety of weak faceted layers 3' below the surface. For the most part these have adjusted to the current load, however with an additional load today (new snow and wind) they have the potential to re-activate. This means either a storm snow avalanche could 'step-down' and trigger and deeper slide lower on the slope, or a slab could fail initially in these old weak layers. Either way, Northern aspects harbor potential for large slab avalanches.

If you find yourself hunting for fresh snow after this storm, be aware that a slab avalanche breaking in old snow 3+' down is possible on steep North facing terrain. 


Mountain Weather

Yesterday patches of sun broke through the clouds following a storm on March 7th that brought gale force winds and 12” of new snow to higher elevations in Turnagain Pass. Light flurries in the morning left a dusting of new snow along the road on the Northern end of Turnagain Pass. Temperatures were in the mid 20’s F along ridgetops and reached 40F at 1000’. Ridgetop wind were 10-20 mph from the East.

Overnight winds began to increase around 11pm and as of this morning strong ridgetop winds from the East Northeast are averaging in the 40s (mph.) Tempertures have remained near 31F along the roadside in Turnagain Pass allowing several inches of wet heavy snow to accumulate.

Today’s forecast is calling for .7” of water at higher elevations with an additional .3” of water this evening. This will be in the form of rain near sea level. Ridgetop winds will reach their peak early this afternoon, 30-40mph from the East. Winds are expected to decrease this afternoon into the evening. Temperatures will increase to the mid 30s F by this afternoon near 1000’ causing rain/snow line to move from 500’ to 1500’ as temperatures increase throughout the day. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32  0.2  61 
Summit Lake (1400') 33  0.1  12 
Alyeska Mid (1700') 32  0.42  37 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 22  ENE  22  80 
Seattle Ridge(2400') 25  n/a  22  54 

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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