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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, March 26th 2018 5:17 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger continues to be MODERATE above 1000’ where triggering a hard slab avalanche 2-4+ feet thick is possible. These hard slabs could be found on all aspects and may be remotely triggered from the side or below. Additionally, watch for old wind slabs along ridgelines and give cornices a wide berth. 

Poor snowpack structure exists at Summit Lake and hard slab avalanches remain a concern there as well. Check out the most recent Summit snowpack and avalanche summary if you are headed South of Turnagain Pass.


 Show the Complete North American Avalanche Danger Scale
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.
Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
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Size

As we enter the last week of Marvelous March, we are in a holding pattern of sorts avalanche-wise. The snowpack structure remains poor. Various weak layers in the middle and the base of the pack are persisting, keeping the avalanche danger at MODERATE for triggering a hard slab avalanche 2-4 feet thick. As time passes, the likelihood of triggering one of these dangerous avalanches is decreasing, but with the high consequences conservative terrain choices continue to be recommended. Many folks are taking advantage of the hard-pack snow conditions by long tours and exploring. With this however, keep in mind this avalanche problem is tricky and triggering a slab from the flats below a slope is possible. Being aware of runout zones and considering how far an avalanche could send debris should be in the forefront of our minds this spring.

In case you are just tuning in, our problem layers are from January. They are facets sitting on a slick melt/freeze crust at the mid elevations and facets mixed with buried surface hoar at the upper elevations. The slab on top is 2-4' thick and very hard due to a strong Northwest wind event that ended last Thursday. This wind event caused unusual loading patterns and created a situation where the typical windward slopes (thinner weaker snow) are more loaded and avalanches could be triggered in unexpected places. To show this, observers have found poor structure along scoured ridges and under sastrugi. The last avalanche we know of was Friday (three days ago) in the Girdwood Valley and was remotely triggered from 200 yards away

*Keep in mind that the snowpack may not show any obvious signs before the slope releases. It may be the 10th skier or snowmachiner onto a slope that finds a thin part of the snowpack (a trigger point). It is always good for us to take a moment and visualize the consequences if the slope are exposed to does slide. 

 

This photo is looking up at the Southwest face of Sunburst. This old avalanche was triggered exactly two weeks ago today after the last snowfall event. On that Monday, a storm ended that brought 2-3' of new snow to Turnagain. This snow has now settled to around a foot or less and experienced much wind and sun damage over the past two weeks.


Pastoral Peak on the left and Kickstep on the right. The mountains look deceptively stable with a hard wind and sun affected surface.


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Additional Concern

Wind Slabs

Wind Slabs:  Old hard wind slabs may be lurking on a variety of aspects due to prior unusual loading patterns. Steep rocky terrain, where slabs sit on unsupported slopes, are the most suspect for triggering a wind slab. This type of terrain is also suspect for triggering a deeper slab mentioned above. 

Cornices: Cornices are large in places and the sun and above freezing temperatures can make them more unstable. Give cornices plenty of space and limit exposure underneath them.


Mountain Weather

Sunny skies again filled the region yesterday before cloud cover moved in during sunset. The anticipated snow flurries never developed. Ridgetop winds remained Easterly in the 10-20mph range with the strongest recordings early this morning, gusting to the mid 30's mph. Temperatures have remained in the teens along ridgetops during the past 24-hours but cloud cover has kept valley bottoms warm where stations are reporting 25-30F temperatures this morning.

Today, Monday, expect overcast skies, cool temperatures and moderate ridgetop Easterly winds. There is a chance a few snow flurries could make it down to the ground, but this is more likely on the Southern and Eastern most part of the Kenai Peninsula. Temperatures look to remain in the teens along ridgetops today with valley bottoms hovering in the mid 30'sF. Ridgetop winds are expected to remain in the 10-20mph range from the East. 

For Tuesday and into Wednesday, a front moves through Western Alaska and may bring a light snow to Southcentral. There is much uncertainty as to this system, yet it doesn't look like the Turnagain Pass area will see much snowfall, mainly cloud cover at this point. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 26  79 
Summit Lake (1400') 25 32 
Alyeska Mid (1700') 27  73 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 17  NE  12   34
Seattle Ridge(2400') 23  ESE  17    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: Dec 01, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed November 21 due to inadequate snow conditions. #hopeforsnow
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClosed
South Fork Snow River Corridor: ClosedClosed
Summit Lake: ClosedClosed

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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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