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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, December 6th 2018 7:00 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger remains MODERATE above 2500’ in the Alpine where triggering a wind slab in steep terrain will be possible. Additionally, triggering a slab avalanche 1-3’ thick, releasing on buried surface hoar, is possible though trending toward a lower likelihood.

SUMMIT LAKE: A very shallow snowpack exists, but triggering a slab large enough to bury a person is possible in the upper elevations.


 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
0 NO RATING Below Treeline / Below 1,000'
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Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
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Unlikely

Chance

Historic
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Overnight moderate Easterly ridgetop winds were accompanied by 2-3” of new snow in the upper elevations. Be aware of fresh shallow wind slabs on steep leeward features. Earlier in the week moderate winds re-distributed the snow in the alpine and older wind slabs may be hard and hidden. Pillowed snow, cracking and hollow, drum-like sounds are clues wind slabs may be reactive. Yesterday on Tenderfoot observers noted recent wind slab formation on top of weak faceted snow. Wind slabs in the Summit Lake area may be more reactive due to a weaker foundation. As always evaluate the terrain for consequences and avoid terrain traps like gullies, rocks, trees below. Also keep in mind very little snow exists below 2000’.  

Wind drifted snow on Sunburst from Monday (12-3-18)


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
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Possible
Unlikely

Chance

Historic
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In the upper elevations we are keeping tabs on a thin layer of buried surface hoar sitting 1-3' below the surface. This layer has been documented in a number of snowpits above 2500’ over the last week. In many places this layer is laying down and unreactive, where in other places it may be upright and still able to propagate. Overnight 3” of snow fell above 2500’ in Turnagain Pass and Girdwood. This isn’t enough weight to be concerned about natural activity, but it could be adding some stress to the snowpack. As always use safe travel protocol and obvious clues like ‘whumpfing’ may not be present.

*Also be aware of a shallow snowpack with weak faceted snow near the ground in the Summit Lake area. Persistent slabs may be more reactive in this zone and could be large enough to bury a person on a large connected slope.

Surface hoar found 2' below the surface on Sunburst on 12-3-18

 

In this area there wasn't much of a slab, but be aware of facets under wind drifted snow in Summit Lake. This structure was found in most hand pits above 2500' on Tenderfoot. 


Mountain Weather

Yesterday: Temperatures increased from mid-20F’s to mid-30F's in the mid-elevations. Light rain started falling below 1000’ yesterday and 2-3” of new snow fell in the upper elevation overnight. In Portage where precip totals are typically higher 0.5” of rain fell near Bear Valley. Ridgetop winds were moderate from the East 15-35mph overnight.   

Today: Temperatures will remain in the mid to upper-30F’s near sea level and rain snowline is expected to be around 1300’. Precipitation below this elevation will fall as light rain (up to .15” of water) and another 1-2” of snow is possible in upper elevations. Easterly ridgetop winds have already started to decrease into the 5-15mph range, but will increase again this evening.

Tomorrow: Get ready as a fast moving system moves into Prince William Sound and with it another round of strong winds, warm temps and a period of heavy rain for our region. Expect above freezing temps in the lower to mid-elevations with rain/snow line around 1500’. Easterly winds will build overnight into sustained 30-40’s mph ridgetop winds with gusts up to 50’s mph.

* Warm temps and winds have finally freed up the Seattle Ridge Anemometer. Wind data is from 12pm - 6am. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 35  0.3  16 
Summit Lake (1400') 26  trace  0.1 
Alyeska Mid (1700') 35  0.25  *N/A 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 27  ENE  12  38 
Seattle Ridge(2400') 31  ESE  12  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: Mar 22, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: Open
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of 3/22. Unfortunately HEAVY rain over the past week has washed much of the snow off the lower stretches of this trail.
Primrose Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: Open
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
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.


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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