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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, February 28th 2018 4:35 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 Monday's storm snow combined with moderate to strong winds over the past two days. 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. 

There was a skier trigger avalanche yesterday in Summit Lake. Read the Saturday Summit Summary HERE and current observations 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.
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

Lost Lake Trail, Primrose Trail, South Fork Snow River Corridor and 20 Mile are all open for motorized use as of today. At 20 Mile please cross the railroad tracks at the designated spot as you leave the parking area.

If heading to Lost Lake area check out an observation describing a snowmachine triggered avalanche that occured yesterday HERE.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday there was evidence of the winds moving Monday's snow around across the region. Scouring, anti-tracks and drifting were observed, especially along upper elevation ridges. A few small natural winds slabs from right after the storm were observed with the crowns mostly filled in.  There were no reports of human triggered winds slab avalanches in the advisory area but there was wind slab triggered in Summit Lake by a party skinning on the Tenderfoot ridge and a snowmachine triggered wind slab in Lost Lake. Northwest winds picked up in the evening and are forecast to remain strong throughout the day today. There is still some snow available for transport. Expect loading and slabs along ridgelines and look for pillowed or drifted snow. Northerly winds can funnel though Turnagain Pass from the South (especially at lower elevations) 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. Slabs may be stiffer and harder to trigger today. They may be initially supportable and then fail above once out onto the slab. 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. 

Sunshine:  Remember that it is that time of year when we need to pay attention to the sun.  The sun can heat up Southerly aspects, and melt surface snow and cause small point releases in the loose new snow. This will be more of a concern if winds become calm this afternoon. This heating can also cause a slab sitting on a weak layer to become more reactive. Avoid steep solar aspect if you notice the surface snow becoming moist or you see roller balls or point releases under rocks. 

Wind effect on Eddies

Skier triggered sluff on Seattle Ridge

 Snowmachine triggered wInd slab Lost Lake. 

 


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 snow load Monday, combined with the winds over the past two days, has added to the overall weight/stress from the small storms 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 finding both layers Monday in their snowpits. 

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. 

 


Mountain Weather

Yesterday was partly cloudy. Temperatures at upper elevations were in the single digits while the valleys were in the teens to low 20Fs. Winds shifted in the morning from SW to NW. Winds were light to moderate during the day and picked up in the evening gusting into the 60s on Seattle Ridge. Skies cleared overnight. 

Today will be sunny and temperatures will be in the single digits at upper elevations and 20Fs at lower elevations. Winds will continue from the NW 20-30 mph gusting into the 40s during the day. They are forecast to slowly diminish overnight and into tomorrow. 

Sunshine continues Thursday with slightly warmer temperatures and light winds. Clouds move in on Friday and there is a chance of snow over the weekend and into next week. Stay tuned for details! 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 20  73 
Summit Lake (1400') 11   0    30  
Alyeska Mid (1700') 12   0    65

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  2  NW  9 51 
Seattle Ridge(2400')  8  NW  25 66 

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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