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Avalanche Advisory

Turnagain Area Avalanche Advisory
Tuesday, February 27th 2018 4:39 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 at all elevations due to yesterday's storm snow combined with moderate to strong winds overnight. Human triggered wind slabs 1-2' thick will be possible. Expect loose snow sluffs in steep protected terrain. Additionally, old weak layers deeper in the pack may be triggered, creating a larger avalanche. Evaluate snow and terrain carefully. 

 


 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.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Special Announcement

Dangerous avalanche conditions are expected in areas seeing new snow such as Hatcher Pass and the Western Chugach. See the Hatcher Pass Avalanche Center Facebook page - avalanche danger has increased to CONSIDERABLE.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday snow fell throughout day with storm totals ranging from 10-15+ inches of low density snow. Avalanche activity reported yesterday was limited to easily initiated loose snow sluffing and small storm slabs. The winds increased last night from the West gusting as high 58 mph on Sunburst. The storm snow is so light that it will have likely been blown into wind slabs that may be tender today. Expect loading and slabs along ridgelines and look for pillowed or drifted snow. The winds are forecast to shift to more Northerly today and there maybe loading on multiple aspects. Watch for shooting cracks and areas with stiffer snow. Steep, unsupported slopes that are loaded will be the most suspect. Look for blowing snow and pay attention to changing conditions.

Loose snow avalanches (sluffs): On steep slopes protected from the wind expect the new snow to sluff easily. These loose snow avalanches may be fast running and entrain snow quickly. 

Sunburst winds yesterday and overnight.

 

Look for loading patterns across the terrain today. 

  

 

 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The overall snowpack structure across the advisory area is poor and it is important to keep in mind that larger slides breaking in persistent weak layers could still occur.  The new load yesterday added to the weight from snow and winds over the weekend and earlier last week. This incremental loading can slowly overload weak layers making them more prone to triggering. Furthermore, avalanches triggered in the upper layers of the snowpack, like a fresh wind slab, have the potential to step down to the buried weak layers. In the upper elevations a layer of buried surface hoar from Jan. 21st continues to show signs of reactivity and in the mid-elevations a layer of facets over a melt-freeze crust is suspect. Observers on Tincan noted both layers yesterday. 

Deep Persistent Slabs:  At the high elevations above 3,000', deeper persistent layers could 'wake up' if the wrong spot is found. 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. 

Snowpack structure on Magnum. The slab depth over the buried surface hoar and facets has now increased.


Mountain Weather

Yesterday snow fell throughout the day. Storm totals ranged from 10-15 inches of low density snow. Winds were Southerly 10-20 mph during the day. They shifted to the West in the evening and increased to 15-30 mph with gusting into the 40s and 50s. Temperatures were in the teens and 20Fs. Temperatures steadily dropped overnight into this morning.

Today is forecast to be mostly to partly cloudy with temperatures in the single digits to low teens. There is a chance of snow showers this evening. Winds will be Northwesterly 10-20 mph gusting into the 30s. They are forecast to increase overnight. 

Tomorrow look for clearing skies, sunshine and temperatures in the teens. Northwesterly winds may continue tomorrow. The sunshine continues Thursday and then clouds build with a chance of snow over the weekend. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  24  8  0.2  74
Summit Lake (1400')  18  3  0.4  31
Alyeska Mid (1700')  20  5  0.24  67

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  13 ESE-WSW  17  58 
Seattle Ridge(2400')  17 E-W  15 40 

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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