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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, January 15th 2019 7:00 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is MODERATE above 1,500'. Wind slabs 1-2' thick will be possible to trigger on steep wind-loaded slopes. Evaluate snow and terrain carefully. In addition, glide cracks may release into avalanches; limit/avoid exposure under them. Give cornices a wide berth.

SUMMIT LAKE / JOHNSON PASS: Keep in mind buried weak layers exist in the middle and base of the snowpack. More potential for triggering a large slab avalanche exists in this zone, especially in terrain that was recently wind-loaded. 

 


 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.
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Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

After ten days of high pressure the advisory area was impacted by a storm over the weekend. Strong easterly winds scoured ridges and loaded slopes. Overall snowfall amounts from ranged from 4-6" at Turnagain Pass to a foot at upper elevations in Girdwood Valley. Observers yesterday noted a few naturals that occurred during the storm with more activity in and around the Girdwood area. Although the winds have calmed down wind slabs are still possible today on steep wind-loaded slopes. It will be important to be careful on terrain that looks pillowed or appears "fat". Look for loading patterns i.e. is the slope cross-loaded or top-loaded? Watch for shooting cracks and listen for hollow sounds. These are signs of hard snow over softer snow and indicate wind slab potential. The snow that fell over the weekend landed on weak surface snow comprised of near surface facets and surface hoar. This weak snow was easy to spot under the new snow yesterday in quick snow pits. Below around 1800' there is a significant breakable crust from where wet snow and/or rain depending on elevation fell on Sunday and then froze as the skies cleared Monday morning. 

Cornices: As always remember cornices may break farther back than expected and if they fall have the potential to trigger slabs on the slopes below. 

Natural avalanche on the south side of Raggedtop. Note the wind loading pattern. 1-14-19.

Weak snow buried under the weekend storm snow, 1-14-19.

 

 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

South of Turnagain - Johnson Pass/Summit Lake zone: A poor snowpack structure exists in these areas and strong winds over the weekend have loaded leeward slopes.  In addition to the recently buried weak surface snow the Christmas buried surface hoar has been found; as well as concerning facet/crust combinations in the bottom of the snowpack. Avalanches may initiate near the ground and be quite dangerous. If you're headed this way, evaluate terrain exposure and the snowpack as you travel. Be on the lookout for signs of instability. 

 


Additional Concern

Glide Avalanches

Many glide cracks got covered with snow/wind filling them in and may be hard to spot. Remember the known areas with cracks are Eddies, Tincan, Sunburst, Magnum, Cornbiscuit, Lipps, Seattle Ridge, Johnson Pass, Lynx Creek, Summit Lake, Petersen Creek, and Girdwood. Avoiding/limiting time under these features is prudent as they can release into an avalanche at any time and are completely unpredictable.

 

Lipps, 1-14-19. The glide cracks are harder to spot. 

 Lipps glide cracks, 1-8-19.

 

 

 


Mountain Weather

Yesterday: Skies were partly cloudy. Temperatures were in the 40Fs at sea level and 20Fs at upper elevations. Winds were easterly 10-20 gusting into the 40s decreasing overnight. Skies were clear overnight and temperatures cooled slightly. 

Today: Skies will start off mostly clear and then clouds increase in the afternoon with a chance of snow. Temperatures will be in the 30Fs to mid 20Fs depending on elevation. Winds will be light 5-15 mph increasing overnight with gusts into the 30s. 1-5" of snow is forecast to fall overnight with rain/snow line around 900'.

Tomorrow: Cloudy skiestemperatures in the 30Fs to mid 20Fs and continued rain/snow showers. The overall trend for the week is mostly cloudy skies with a chance of rain/snow showers and temperatures in the 20Fs and 30Fs.  

*Seattle Ridge weather station was heavily rimed and the anemometer (wind sensor) was destroyed. We are currently working to replace it.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 33  53 
Summit Lake (1400')   26     22  
Alyeska Mid (1700') 32   0   41 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  25  NE 14  43 
Seattle Ridge(2400')   29   *N/A *N/A  *N/A 

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: May 06, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
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: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Closed

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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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