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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Thursday, December 18th 2014
Created: Dec 18th 6:37 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'
 Show the Complete North American Avalanche Danger Scale
TOTE Maritime
Special Announcement

Join CNFAIC forecaster John Fitzgerald (Fitz) tonight for the 3rd installment of our Fireside Chat series.  Fitz will be presenting on Human factors and decision-making in the backcountry tonight at the Glacier Ranger Station in Girdwood, 6:30PM.


The Bottom Line

The avalanche danger is CONSIDERABLE today in the upper elevations of the forecast area.  This includes terrain above 2,500’ where recent storm snow has been deposited on a weak layer/ bed surface combination.  With our current snowpack structure, human triggered avalanches in the 2-5’ range are likely today.  Below 2,500’ the avalanche danger is MODERATE primarily due to the potential of avalanches initiating higher up and running into this lower elevation band. 

Cautious route finding and conservative decision-making will be essential today to avoid slopes greater than 35 degrees.  This includes run out zones and terrain connected to steep, avalanche prone slopes.


Primary Concern

We had little trouble finding a layer of buried surface hoar in our snowpits yesterday.  It is present and reactive, as expected above roughly 2,700’ where the snowpack dries out significantly.  This current set up consisting of a stout crust (bed surface) capped by surface hoar (weak layer) and buried by a fresh slab (strong snow) is sort of a ‘perfect storm’ for avalanches.  We have seen this over the last 48 hours with several natural avalanche observations coming in from across the region.  The commonality with this most recent avalanche cycle is that slides are initiating in the dry snow at upper elevations and very likely running on this layer of buried surface hoar.  Today the message is simple: avoid terrain steeper than 35 degrees, and make conservative travel decisions.  This includes the terrain adjacent to or directly under avalanche slopes as the nature of this weak layer/ bed surface combo can allow for wide propagation and triggering avalanches remotely, including from below.

In the lower elevations (below ~2,500’) where the snowpack is moist, the slab appears to be gaining strength over time and as temperatures drop.  The primary concern in this elevation band is one of exposure from alpine start zones.

                    Quick snapshot of the bed surface/ weaklayer/ slab combo found in the mid to upper elevations of Turnagain pass.  This snowpit is at 2,800' on the west ridge of Sunburst (common approach).

 


Mountain Weather

The most recent storm (Saturday – Tuesday) brought another slug of unseasonable warm temperatures into our region with rain at sea level and the snow line fluctuating between 1,500 – 2,000’.  Yesterday was an attempt for the weather to return to something closer to ‘normal’ with the snow line dropping to around 500’ in the eastern Turnagain arm region.  Locals in Girdwood even called in to report sighting of snowflakes hitting the valley floor (though not sticking)!  With temperatures fluctuating around 34 degrees at sea level it was still mostly rain yesterday.

In Turnagain pass (1,000’) the temperature was right at 32 degrees during the daylight hours with skies producing off and on snow showers and 1-2” of accumulation.  Winds yesterday were consistently from the east in the 10-20mph range and a few gusts into the 30’s.

Today’s weather looks to be on the quiet side as we are in between storms and should be feeling the effects of a short wave ridge of high pressure.  Temperatures at a1,000’ will be in the low 30’s with perhaps just a trace of snow falling.  Expect winds to be in the single digits today at ridgetop locations, shifting slightly to a northeasterly direction with the approach of our next low pressure system.

We’ll begin to feel the effects of a powerful low-pressure system spinning into the Gulf of Alaska late tonight and into tomorrow.  Our rain/ snow line should hold around the 500’ level with snow falling through Turnagain pass.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30   .1  29
Summit Lake (1400')  28  0  4
Alyeska Mid (1700')  31  5 .4  19 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  12  34
Seattle Ridge(2400')  25 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: 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

Subscribe to the Turnagain Area Avalanche Advisory:

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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