Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Wednesday, February 25th 2015
Created: Feb 25th 6:47 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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The Bottom Line

Today in the Alpine the avalanche danger is CONSIDERABLE where a slab 1-3’ thick if triggered is likely to have high consequences. It is in the Apline where it will be important to avoid large slopes steeper than 35°. Below 2500’ the danger is MODERATE where an avalanche if triggered from above could run into this elevation band.

Cautious route-finding and conservative decision making should be at the forefront of our minds today, especially if being tempted by sucker tracks. This is the kind of avalanche problem where a person may ski/ride a steeper slope and nothing happens, but the 2nd or 3rd person could trigger a large avalanche. 

Primary Concern

Yesterday was the first day of clear sunny weather following a warm and wet weekend of rain to 2500’ and 3-6” of new snow at higher elevations. Cooler temperatures have created a crust layer along the surface that is adding strength to the snowpack at mid elevations. Above 2700’ where this surface crust does not exist a softer slab 1-3’ thick is sitting on a widespread layer of facets.

This new snow looks very much like the classic Maritime snow we so often associate with stable conditions, but lurking below is an already stressed weak layer + thick slab that formed on Feb.16.

We currently don’t have a lot of information about how much force it will take to trigger an avalanche in the upper elevations. What we do know is that the weak layer is widespread throughout the region and test pit scores are showing moderate strength with high propagation potential. Meaning - if a slab is triggered an avalanche of its size is likely to have high consequences. This is why the danger for the Alpine will remain at CONSIDERABLE for today.

As we move away from this most recent loading event obvious signs like collapsing and shooting cracks will become less common. This could be deceiving because this also means that the weak layer will become harder and harder to trigger yet the consequences will remain high for awhile. This is a good reminder to be patient and stay off of steep slopes until conditions become more stable. 

This is a picture of the surface crust at 2000' on Sunburst yesterday. This crust gradally gets thinner as you gain elevation and disappears completely at 2700'. 

Mountain Weather

Yesterday morning a trace of new snow fell at Turnagain Pass, just enough to cover the bare ground for a few hours before mid day temperatures (low 30's F) melted most of it away. At higher elevations temperatures stayed in the mid 20’s F and North winds averaged 5-15mph along ridgetops. Skies were sunny and with thin cloud cover later in the day.

Overnight temperatures remained in the low to mid 20’s F. Ridgetop winds were from the North and averaged 5-15 mph. No new precipitation was recorded.

Today light cloud cover and patchy fog will become mostly clear by this afternoon. Temperatures will be in the 20’s F and are likely to increase into the low 30’s F mid day with sunny skies. Ridgetop winds should remain light to moderate from the North, but winds are expected to increase near Whittier throughout the day into the evening. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29  trace .01 40 
Summit Lake (1400') 29 
Alyeska Mid (1700') 30  trace .04 23 


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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  N/A  N/A  N/A 
Seattle Ridge(2400') 24  NNW  21 

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: Apr 28, 2017 )

Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: OpenOpen thru May 14th.
Twentymile: Closed
Seward District
Carter Lake: OpenClosed May 1.
Lost Lake Trail: OpenClosed May 1.
Primrose Trail: OpenClosed May 1.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: OpenClosed May 1.
South Fork Snow River Corridor: OpenClosed May 1.
Summit Lake: OpenClosed May 1.

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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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