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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Saturday, March 4th 2017
Created: Mar 4th 5:42 am
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
Special Announcement

Strong winds over the past several days have affected the snow/avalanche conditions in many areas of Southcentral Alaska and the Kenai. See this report sent in to us from the Lost Lake zone on the Southern Kenai. Additionally, a natural avalanche was viewed in motion in the South Fork of Eagle River yesterday. For avalanche conditions at Hatcher Pass, see the HPAC Saturday morning advisory!

Avalanche Rescue Talk:  Stop by Ski AK in Anchorage for a discussion on backcountry rescue Tuesday evening! The focus will be on organized rescue, presented by Bill Romberg (AMRG) a rescue specialist with 150 Search and Rescue missions here in Alaska. The evening will begin with a short 'state of the snowpack' report by the CNFAIC. See you Tuesday night - more details HERE!!


The Bottom Line

The avalanche danger is MODERATE on slopes above 2,000' that have seen wind loading by sustained Northwest winds. Although these wind slabs are expected to be very stiff and stubborn to trigger, the possibility remains that slabs could release in steep rocky terrain. In areas that have seen less wind, such as many slopes in the core forecast area of Turnagain Pass, triggering a wind slab is unlikely. 

There is a LOW avalanche danger on upper elevation slopes without recent wind loading and all slopes below 2,000'.  

*In Summit Lake, Girdwood Valley, and on the southern end of the forecast zone a generally shallower snowpack exists with a poor structure. Wind loaded slopes in these areas have the potential to step down and trigger a deeper avalanche. Please see the Saturday Summit Summary HERE.


Primary Concern

As Southcentral Alaska sits under a cold, clear and very windy weather pattern, there are areas that have been partially spared by the brunt of the Northwest winds. The ridges along the East side of the road along Turnagain Pass are one of these areas. Folks have been able to find some soft snow and venture further into the mountains without incident. That said, there are areas that have not escaped the major winds. An example would be the Crow Pass region of the Girdwood Valley and the mountains on the Southern end of the forecast zone toward Silvertip. In the Summit Lake area (Summit Snowpack Summary here) two avalanches were seen yesterday on Summit Peak. The key, of course, is to find these sheltered areas, both for better riding conditions but clearly for decreased avalanche danger.

Wind slab avalanches:

It will be another day to watch for slopes with recent or current wind loading. Ridgetop winds should again be moderate to strong - in the 15-25mph range from the Northwest. However, there is not nearly as much snow to blow into slabs as there was at the beginning of this wind event 4-5 days ago. Most of the loose surface snow has blown away or been blown into hard slabs, crusts and sastrugi at the higher elevations. Things to keep in mind with wind slabs:

  1. Wind slabs are expected to be very hard and stiff (supportable to boots and snowmachines)
  2. They are likely to be stubborn and tough to trigger
  3. Steep rocky terrain is the most likely place to trigger a slab

  

Cornbiscuit Ridge on the East Side of Turnagain Pass - one of the 'less windy' areas.


Additional Concern

It is good to keep in mind that there are areas in the periphery of Turnagain Pass that have a poor snowpack structure. These layers are buried surface hoar 1-3' deep and facets in the mid and base of the snowpack. The 'wind event' has loaded and reactivated some of these older layers. The most recent avalanche activity was seen yesterday in the Summit Lake area. Besides Summit Lake, other areas of concern include the Johnson Pass zone and some areas in the Girdwood Valley. Continual winds with this relentless wind event may be loading these old weak layers to the point of failure.

Recent natural wind slabs in the Summit Lake area, this is just to the South of the forecast zone, seen and documented yesterday. (A bit complicated, but the point is two of the 4 avalanches in the photo occurred yesterday).


Mountain Weather

Brilliant sunny skies were over the area yesterday with very cold temperatures at all elevations - in the single digits and minus single digits. Daytime warming allowed the mid and lower elevations to warm into the upper teens and have only cooled a few degrees overnight. Ridgetop winds during the past 24-hours have averaged near 10mph with gusts into the 30's from the Northwest. 

As Southcentral Alaska sits in a holding pattern of sorts, we can expect similar sunny skies today with continued Northwest winds. Temperatures should warm again today into the upper teens below 3,000'. Ridgetop winds are expected to remain from the North and West in the 15-25mph range with stronger gusts. 

For Sunday, sunny and cold weather remain. The one change could be another pulse of stronger Northerly winds. This blocking pattern of high pressure over Alaska looks to remain for the rest of the week. Keep tabs on what the NWS is finding at the bottom of their Forecast Discussion - Long Term Forecast!

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 10  63 
Summit Lake (1400') 29 
Alyeska Mid (1700') 12  58 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') NW  10  31 
Seattle Ridge(2400') 10  NW  10  34 

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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