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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, March 27th 2018 5:19 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 1500’ on all aspects. Triggering a hard slab avalanche 2-4 feet thick remains a possibility. These hard slabs can be remotely triggered from the side or below. Additionally, watch for old wind slabs in steep rocky terrain and give cornices a wide berth. 

Similar avalanche concerns exist in the Summit Lake area  and other zones on the Kenai.


 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
Large
Small

Size

Triggering a hard slab avalanche is still our primary concern in the backcountry despite the quiet weather. It has been over two weeks since the last snowfall event and four days since the last human triggered avalanche; yet with the hard-pack surface conditions, there haven't been many folks out lately testing the slopes. Hiding under the snow surface are weak layers in the snowpack that just will not go away. However, with time they are becoming more and more difficult to trigger, trending toward unlikely. Hence, we are in a low probability, high consequence situation. The tricky part about this is, the pack appears to be stable but the chance remains for an unmanageable and destructive avalanche if a person hits just the wrong spot. 

To recap, the weak layers in question were formed back in 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 avalanches could be triggered in unexpected places for those with a lot of familiarity of the area.

With sunny skies forecast later this week and partly cloudy skies today and tomorrow, there is little in the way of weather that will impact our old and tired snowpack - except for the sun. We can't forget that spring is here; even though temperatures have been relatively cool, this could change any day now. Many folks are taking advantage of the snow conditions by long tours and exploring. If this is the case, know that 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. Additionally, no obvious signs of instability may be present before a slope releases and it may be the 10th skier or snowmachiner onto a slope that finds a trigger point. 

 

Goat Mountain and Goat Couloir pictured below with some old debris down the main chute. There is also what could be newer debris from last weekend coming from steep rocky terrain out of sight on the looker's right. Springtime is here and as rocks warm with the sun, wet loose and wet slab avalanches should be on our radar. We don't want to be in the path of even a small wet slide.

 

Seattle Ridge - this Southeast facing terrain (that faces the Seward Hwy) is one of the first areas to have wet avalanches during the onset of the spring warm-up. So far the snow remains cold and crusty, but this could change quickly if sun and warm temperatures arrive this week. 

 

 

 

Other avalanche issues to keep in mind: 

Wind Slabs:  Old hard wind slabs are sitting on a variety of aspects due to prior unusual loading patterns. Watch of these slabs to possibly pull out in steep rocky terrain where slabs are unsupported from below. This type of terrain (steep unsupported slope) is also suspect for triggering a deeper slab mentioned above. 

Cornices: Many cornices are quite large and teetering over. Temperatures have been cool lately but as we head into warmer, sunnier weather remember this can help de-stabilize them. As always, give cornices plenty of space and limit exposure underneath them.

Wind effect on the Seattle Ridge headwall. Note the cross loading above the rocks on the slope in the back, this is an example of loading on 'unsupported' slopes.


Wind effect in the Seattle Creek drainage (photo: Troy Temple)


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Mountain Weather

Partly cloudy to overcast skies were over the region yesterday. Ridgetop winds were moderate from the East (15-20mph) before decreasing to light and variable overnight. Temperatures hovered near 20F along ridgetops and warmed to the low 30'sF at 1,000' with daytime warming before cooling into the mid 20's overnight.

Today, Tuesday, partly cloudy skies are on tap. It's one of those days where the sun could shine more than expected before thicker clouds move in overnight. Ridgetop winds will be generally light from a Westerly direction (5-10mph). Temperatures look to remain near 20F along ridgetops and could warm to the mid 20's with daytime warming. Valley bottom temperatures are in the teens this morning and should warm to the low 30'sF.

Wednesday morning, cloudy skies with a chance for a few flurries are expected as we sit on the outskirts of a low-pressure system rotating in the Bering. By Wednesday evening through the rest of the week, high pressure builds in bringing sunny skies. So far, the winds associated with the clear skies look to remain light and Northerly.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 28  78 
Summit Lake (1400') 27  31 
Alyeska Mid (1700') 29  72 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 18  NE  13  35 
Seattle Ridge(2400') 24  11  36 

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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