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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Tuesday, February 28th 2017
Created: Feb 28th 5:28 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.
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.
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
The Bottom Line

There is a MODERATE avalanche danger on all aspects above 1,000' where triggering a shallow fresh wind slab avalanche is possible. Recent strong winds have formed fresh wind slabs on a variety of aspects both near ridgelines and possibly further down slopes. Watch for these on leeward features where winds have drifted snow. There also remains a possibility of triggering a more stubborn, yet more dangerous, slab avalanche 2-3' thick due to a layer of buried surface hoar on slopes above 2,000'. In addition, be aware of cornices, surface sluffs, and a glide crack that continues to open up on Seattle Ridge. 

Below 1,000' there is a LOW danger where triggering an avalanche is unlikely.

In the Summit Lake, Girdwood Valley, and on the southern end of Turnagain near Johnson Pass, a poor snowpack structure exists where weak faceted snow sits near the ground. Check out the Saturday Summit Summary HERE.


Primary Concern

Don't put away your hand warmers and cold weather gear yet! It seems as though spring will have to wait as very cold air is currently streaming down from the North. For those out in the mountains yesterday, during the afternoon a dramatic change in weather took place as strong Northwest winds kicked up and temperatures plummeted. Overnight some ridgetops are reporting temperatures in the minus single digits...

Wind Slab Avalanches:
The strong Northwest winds peaked early last night, with hourly averages near 40mph. As of this morning, the winds have decreased, but still remain in the moderate category, averaging 15-20mph. Although there were only a few flurries associated with the wind, there is/was 4-8" of loose snow already on the ground available to be blown into slabs. These are expected to be in the foot thick category and found in exposed areas out of the trees. Some things to keep in mind today:

  1. New wind slabs could be both soft and hard depending on the strength of the winds in specific areas
  2. They could be further down the slope than expected due to cross loading
  3. All aspects are suspect! This Northwest flow tends to be channeled through Turnagain Pass such that Southerly winds are seen on the East side of the highway - loading Northerly slopes
  4. Pay close attention to surface texture and areas of wind scouring and wind loading
  5. Watch for hollow feeling snow, strong and stiff snow that sits on softer snow
  6. Until proven otherwise, expect wind slabs to be touchy and easy to trigger

 

Photo: Strong Northwest winds were transporting snow onto an Easterly face along ridgelines yesterday in the Girdwood Valley. 

 

Cornices:  Winds have, and will be, adding more snow to the already large cornices. Remember these unpredictable hazards can break farther back along ridgelines than expected and have the potential to trigger an avalanche on the slope below. Give them extra space and avoid being under them. 

Loose snow avalanches:  If you find terrain that is protected from the winds and harbors loose soft snow, expect to initiate sluffs on steeper slopes. 


Secondary Concern

Unlike the avalanche concerns associated with the winds, that are easily seen on the surface, we must remember there are lurking weak layers deeper in the snowpack. A widespread layer of buried surface hoar (buried on Feb 9th) sits anywhere from 2-3' below the surface. This layer continues to be found in most pits and although it is becoming very tough to trigger, it does continue to show potential to fail and propagate. For a better look at this, check out the video in our report from the Girdwood Valley yesterday.

The bottom line here is, there is still a chance that a 2-3' slab could be triggered on steep slopes above 2000'. It has been 9 days since an avalanche was triggered on this layer and folks have been able to push further into the mountains without incident. However, with added load by winds and the chance a person could accidentally find the right trigger point, these larger slab avalanches remain a concern. Likely trigger spots are in places where the snowpack is thinner - near rock bands or on more scoured features. These slabs can break above you, and release after several tracks are on a slope. Be aware that no red flags may be present.

Deep Persistent Slab: We continue to find various layers of weak faceted snow and depth hoar near the bottom of the pack in certain areas. This includes Summit Lake zone, and some areas in Girdwood Valley and towards the Southern end of Turnagain near Johnson Pass. Similar to the problem above, these layers will be very tough to trigger, but a possibility remains in places with this structure.


Additional Concern

Glide avalanches:  The glide crack looks to be continuing to open above the flats along Seattle Ridge, just looker's left of the up-track and Repeat Offender slide path. Avoid hanging out under this crack and any others you may see.

 


Mountain Weather

Mostly cloudy skies with a few flurries here and there were seen yesterday, Girdwood Valley picked up 0.5" of snow but other areas only saw a trace. During the afternoon, the Northwest winds picked up dramatically in many areas - Seattle Ridge weather station reported gusts up to 64mph with hourly averages up to 41mph. Sunburst weather station on the other hand does not pick up this NW flow very well and reported significantly less wind. Very cold temperatures are being ushered in by the wind and overnight ridgetops have dropped to the single digits.

Today, cold air will continue to pour into the region from the Northwest with ridgetop winds in the 15-25mph range. Minus single digit temperatures are expected at the upper elevations while valley bottoms should be around 10F. No precipitation is expected and skies should be mostly clear.

For the remainder of the week, partly sunny skies with very cold temperatures should persist. While no new snow is in the forecast, we should see the gusty Northwest winds decrease.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 13  trace  66 
Summit Lake (1400') 20   0 31
Alyeska Mid (1700') 19  0.5  0.03  60 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 11  NW   30
Seattle Ridge(2400') 16  NW  24     64 

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: Mar 15, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: Open
Skookum Drainage: OpenSkookum drainage closes to motorized use on April 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
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: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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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