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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, February 21st 2018 5:15 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 1,000' on all aspects. Human triggered slab avalanches 1-2' thick remain possible. Additionally, weak layers deeper in the snowpack may still be triggered, creating a larger avalanche. 

The Summit Lake area saw more avalanche activity last week. Take a look at the Summit Summary HERE. 

 


 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

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a slab avalanche 1-2+ feet thick continues to be our main concern. There has been mostly quiet weather and lack of people triggering avalanches over the past week. However, in observations across the region the January 21st layer of buried surface hoar and a variety of other layers of weak snow continue to show signs of reactivity. Notably at lower elevations there are facets over melt-freeze crust that are also still showing triggering potential. Persistent slabs are becoming more difficult to trigger with time, but a large and unmanageable avalanche is still possible. Weak layers in the snowpack below your feet or snowmachine should not be forgotten.  Red flags may not be present before a slope releases and it may not be the first person on the slope that triggers the avalanche. The most likely place to find this avalanche problem are slopes that have not seen significant traffic this season. 

Deep Persistent Slabs: Keep in mind that there are deeper persistent layers that could 'wake up' if you find the wrong spot above 3,000' in the Alpine. At these high elevations, old weak layers of facets and buried surface hoar sit in the bottom half of the snowpack. This structure is most pronounced in places with a thin overall snow cover, such as the South end of Turnagain Pass, the Summit Lake area and Crow Pass. 

Lower elevation snowpit on Eddies showing more than one weak layer of snow present in the snowpack. 

 


Additional Concern

Wind Slabs

Wind Slabs:  Watch for old wind slabs that could pop out on steep slopes. These hard slabs often break when you are out onto them. Steep rocky terrain where the slab is not supported from below is the most suspect. 

Cornices:  Avoid traveling under cornices and give them a wide berth on ridges, as they can break back further than expected.

Sunshine:  It's that time of year when we need to pay attention to the sun. On calm days the sun can heat up Southerly aspects enough to melt surface snow. This heating can also cause a slab sitting on a weak layer to become more reactive. Keep this in mind if the sun is shining and you are enjoying Southerly aspects later in the day.

 

 


Mountain Weather

Yesterday was mostly sunny above the valley fog. Temperatures at upper elevations climbed into the low 30Fs and due to the inversion stayed in the 20Fs in the valley bottoms. Winds were westerly 5-15 mph with gusts into the 20s. 

Today will be mostly cloudy with temperatures in the high 20Fs to mid 30Fs. Winds will be light and easterly. There are snow showers in the forecast for this evening with 1-3" of snow possible. 

Tomorrow snow is likely in the morning. Due to warmer air there may be some "mixed precipitation." Temperatures will be in the mid 20Fs to low 30Fs. Winds will be easterly in the morning and shift to the west in the afternoon. There is clearing in the forecast for Friday and then another shot of moisture and precipitation on tap for the weekend. From the NWS this morning: The progressive nature of the pattern will continue through next week, with front and lows rolling into the region every 1-2 days.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27   0  0  63
Summit Lake (1400') 22    0   0  24
Alyeska Mid (1700')  23    0  0  55

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  27  W  23
Seattle Ridge(2400')  28  W   25 

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, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

Subscribe to the Turnagain Area Avalanche Advisory:

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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