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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, March 7th 2018 4:33 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 remains MODERATE above 1000’ on all aspects. Triggering a large slab avalanche breaking in weak layers 1-3' deep in the snowpack is possible. Watch for old wind slabs along ridgelines and in cross-loaded gullies. 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.
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

As we anticipate a storm tomorrow it is good to remember the current state of the snowpack. Observers continue to find the buried persistent weak layers in the snowpack to be reactive and today the possibility of triggering a large avalanche remains. At the mid-elevations, buried 1-2' deep are facets sitting on a crust and at the higher elevations, 1-3' deep is a buried surface hoar/facet combo. The slab over the weak layers could be very hard if it is in terrain that was affected by the strong winds last week. This was the case in the skier triggered avalanche in Summit Lake a week ago, the mid-elevation faceted layer was under very hard wind-affected snow.  Although the heart of Turnagain Pass has the buried weak layers, they are more pronounced and developed on the Southern end of Turnagain Pass and in Summit Lake where the snowpack is shallower. On Monday an observer found the buried surface hoar in Lynx Creek, described the snowpack as "spooky" and changed their plan due to concerning snowpit test results. Areas to the North, such as Crow Pass, are also suspect along with those that have not seen much traffic this season. Using safe travel protocols and assessing the consequences if a slab does release is key in choosing terrain. Weak layers like these can become more reactive after even a small additional load. As the snow falls this week keep that in mind and as always be alert for signs of instability. If we do get heavy snow tomorrow expect the avalanche danger to rise quickly.

Wind slabs: Hard wind-affected snow on steep, unsupported slopes may still triggered if you find the wrong spot. Be suspect of very stiff snow over soft snow or hollow sounding snow near upper elevation ridgelines and cross-loaded gullies. In addition, yesterday afternoon the winds picked up blowing from the East and gusting into the 30s. Look for cracking and very shallow, fresh wind slabs near ridgelines. 

Solar warming/effects:  Sunshine this afternoon may allow for enough warming to initiate roller balls and small wet loose avalanches on steep Southerly aspects. Warming may also cause slabs to be more reactive; something to keep in mind as we choose our late afternoon terrain.  

State of the snowpack before the storm... 

 The Tenderfoot avalanche that occured last week due to very hard wind-affected snow over the buried facet/crust combination.

 

 


Mountain Weather

Yesterday was mostly cloudy with light snow showers in the afternoon into the evening with little overall accumulation. Temperatures were in the teens to mid 20Fs. Winds were picked up in the afternoon blowing Easterly 10-20 mph with gusts into the 30s. 

Today will start cloudy and become partly sunny in the afternoon during a small window before the next system moves in. Temperatures will be in the 20Fs to low 30Fs. Winds will be light and Northerly. Clouds move in again in this evening with snow showers overnight. Winds will shift back to the East and temperatures will be in the upper teens to mid 20Fs. 

There is still some uncertainty in the storm track that is forecast to impact the area tomorrow.  The difference of the low moving into Cook Inlet versus Prince William Sound will affect how much precipitation the advisory area gets. There is a good possibility that we will see some periods of heavy snow and stronger winds. The timing and snow amounts are still to be determined. Stay tuned! 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  25 trace   67
Summit Lake (1400')   18  trace   0     29 
Alyeska Mid (1700')  22 1.4  0.11   59

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  13 ENE   11 31 
Seattle Ridge(2400')  19 ESE   15 32 

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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