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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, March 19th 2018 5:07 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

Today is a day of transition. Triggering a large, dangerous slab avalanche 2-4+’ thick is still possible on all aspects and all elevations due to weak snow under a dense slab. However, there are additional avalanche problems closer to the surface.

This morning, the avalanche danger is CONSIDERABLE on all aspects below 1000' where rain is falling. Wet snow avalanches will be likely at these lower elevations before colder temperatures move in later this afternoon. This afternoon, strong winds will impact the region and may increase the avalanche danger to CONSIDERABLE at the upper elevations by tonight where cornice falls and wind slabs may occur naturally. The mid elevation band is expected to remain generally MODERATE. Pay attention to changing snow conditions and remember remote triggering a large slab remains possible. Evaluate terrain consequences and practice safe travel protocol. 

Dangerous avalanche conditions exist in Summit Lake, 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
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.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

UPDATE:  An avalanche has crossed the Hatcher Pass road this morning and the road is closed, most recent information at HPAC facebook page. Significant avalanche activity has occurred this week region-wide from Hatcher Pass all the way South to Lost Lake near SewardCheck out the Hatcher Pass avalanche forecast at hpavalanche.org if you are thinking of heading that direction.

Roof avalanches will continue to be a concern this morning with light rain falling in Girdwood, Anchorage and other areas currently. 


Avalanche Problem 1

Deep Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

This morning will be the final push of warm and rainy weather before skies clear and a cold Northwest wind sets in to freeze the wet and saturated snow. Up to 2-3" of new snow could fall above 1,000'. This dramatic change in the weather pattern is expected around noon today and by late this afternoon, strong winds along with sunny skies are forecast. The cooling trend will stabilize the lower elevations quickly. At the higher elevations, the winds will search out any remaining soft snow, along with any new snow, and attempt to build wind slabs and grow cornices. Wind slabs could be touchy and may release naturally, yet they should be on the smaller side - up to a foot thick. Wind slabs may also overload weak layers deeper in the pack, contributing to a much larger slide.

This larger avalanche issue is our deep persistent slab problem, which boils down to: triggering a large destructive avalanche 2-4+ feet thick is still possible. For the first time in over a week, there were no new slab avalanches reported yesterday. The last avalanche was a snowmachiner triggered slab in Main Bowl of Seattle Ridge on Saturday. This slope had tracks on it from the day before and was triggered from a flatter area below (remotely triggered from below). To recap, over the past week many large human triggered avalanches and/or natural avalanches have released from Girdwood to Lost Lake (please see Heather's video if you have not already). Some of these avalanches have been remotely triggered and some with skier/snowmachiners on the slope. Most of these avalanches have occurred below 3000’, releasing on weak faceted snow on a slick crust, 2-4 feet below the surface. A lot of uncertainty remains in the Alpine where slab depths are much deeper and triggering an avalanche could be more stubborn. Widespread buried surface hoar and facets have been well documented at all elevations. 

*With a deep slab problem it is important to remember no signs of instability may be present before a slope releases. It may be the 10th person onto the slope that finds the trigger point and slopes may be triggered remotely. It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point. 

Main Bowl avalanche from Saturday, March 17th, East aspect. This was a remote snowmachine trigger from below. No one was caught. Photos: Brian Bird


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Until the skies clear and temperatures cool down later today, wet loose and wet slab avalanches remain likely. The exception will be Southerly slopes that see sunshine and are out of the winds. These slopes may continue to see wet avalanche activity through the day. A wet point release could be small to large and has the potential to trigger a much larger, more dangerous slab. Pay attention to the surface conditions and avoid slopes with saturated wet snow. 


Additional Concern

Cornice

Cornices are large and looming. Give these an extra wide berth and limit exposure underneath them. Winds today may find enough snow to add to their size and this along with sun later today, may be enough to cause some of break off naturally. A cornice fall could trigger and propagate an avalanche on a slope below.


Mountain Weather

Mainly obscured and overcast skies filled the region yesterday. Temperatures were warm, in the upper 30'sF at 1,000' and in the upper 20'sF along the higher ridgelines. Winds have been Easterly in the 5-15mph range with stronger gusts during the past 24 hours. Between .1 - .2" of rain has fallen up to 1,000' overnight in the Girdwood Valley, but Turnagain Pass and Summit Lake weather stations are reporting no precipitation.

For today, Monday, we can expect .2-.3" of rain up to 1,000' this morning with 2-3" of snow falling above 1,000'. By the afternoon, skies look to clear as this system moves out and strong Northwest outflow winds move in; ridgetop winds look to be in the 25-40mph range with strong gusts. Temperatures will be warm (upper mid 30's at 1,000' and mid 20'sF along ridgetops) before cooling down with the NW winds this afternoon to the upper 20'sF at 1,000' and teens along the ridgetops.

Tuesday and into the work week, the cold Northwest outflow winds look to remain entrenched for much of Southcentral Alaska. Sunny skies will accompany the wind along with a cooling trend at all elevations.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32  82 
Summit Lake (1400') 34  30 
Alyeska Mid (1700') 33  0.2  77 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  18 
Seattle Ridge(2400') 29  11  23 

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
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