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Avalanche Advisory

Turnagain Area Avalanche Advisory
Saturday, December 15th 2018 5:32 am by Wendy Wagner
Previous Forecast
BROUGHT TO YOU BY
The Bottom Line

The avalanche danger is MODERATE in the Alpine and Treeline. A bump in easterly winds today along with a few inches of snow this morning will likely form fresh wind slabs, up to a foot thick, that could be easy to trigger. If snowfall and wind intensify more than forecast, the danger will rise to CONSIDERABLE. Additional concerns: watch your sluff, as these have been getting larger, and keep an eye out for glide cracks and avoid traveling underneath them.

SUMMIT LAKE:  New snow overnight may overload weak layers near the ground, increasing the chance a person could trigger a larger slab avalanche. 


 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.
Special Announcement

New snow and wind has increased avalanche conditions in zones outside of the Chugach National Forest. #knowbeforeyougo


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Watch for changing conditions. Ridgetop winds have picked up and should be blowing the existing loose surface snow into sensitive wind slabs this morning. These fresh slabs are likely to be shallow, around a foot thick, and easy to recognize if you are looking for them. Watch for areas with wind deposited snow and loading patterns in general. Shooting cracks will be an obvious clue wind slabs are tender. Feel for punchy or upside down snow and keep in mind the consequences of the terrain should even a small slab pull out from underneath you. In areas where winds aren’t an issue loose surface snow could move faster and farther than expected. 

Trevor Grams sent in this photo from the Library area further back along Tincan Ridge yesterday. Note the loose surface snow available for transport with today's winds. 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

As is often the case, the snowpack in the periphery zones of our advisory area such as, Crow Pass and Summit Lake have a shallower snowpack. In these areas, and even those closer to Turnagain Pass itself, we are tracking buried layers of facets and crusts that sit 1-2' under the snow surface. These layers are most prevalent in the mid-elevations (2000’ – 2700’) and though snow pit data and a lack of avalanche activity has been pointing to an unlikely chance for an avalanche releasing deeper in the pack, additional snow load in the Summit area could start to tip the balance. Evaluate the snowpack and terrain as you travel and be aware that obvious clues like whumpfing may not be present.


Additional Concern

Glide Avalanches

Glide cracks are beginning to open up in many places, including Sunburst's SW face under the weather stationSW face of Tincan Proper, Gold Pan area (behind Cornbiscuit/Magnum) and the one shown below in the Johnson Pass area. These cracks can release at any moment, as this one did below in Johnson Pass. They are not associated with human triggers and the best way to manage the hazard is to avoid being on or beneath slopes with cracks. 

 

Photos of the Johnson Pass area glide avalanche couresy of Matt McKee.

 

An unnamed longtime CNFAIC pro observer puts his take on this avalanche problem...


Mountain Weather

Yesterday:  Overcast skies were over region yesterday. Evening snow showers favored the Summit Lake area on the Kenai and further South where 4-6" fell along the Seward Highway. Turnagain Pass and Girdwood only picked up 1-2". This storm also favored the Anchorage region and North with 4-6". Ridgetop winds have remained easterly in the 10-20mph range with gusts in the 30's. Temperatures warmed dramatically overnight and are sitting in the teens along the ridgetops and 20's at 1,000'. 

Today: Snow showers have picked up this morning in Portage Valley and Girdwood. This quick moving front should give the mountains 2-4" of snow before moving out by midday. Ridgetop easterly winds have picked up as well and should stay in the 15-25 mile range with gusts in the 40's. Temperatures continue to rise and are expected to hit the upper 20's at 3,000' and mid 30's at sea level.

Tomorrow:  What looks like a stronger front associated with the low-pressure in the Gulf moves in on Sunday. This should give the Turnagain area another chance to build up the snowpack. Warmer temperatures could bring a rain/snow mix to sea level, but so far it looks like it will be all snow at 1,000'. Stay tuned!

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 20  0.1  30 
Summit Lake (1400') 18  0.5  13 
Alyeska Mid (1700')  21 0.3  17 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 14  ENE  14  41 
Seattle Ridge(2400') 20  *no data  *no data   *no data  

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: Dec 01, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed
Placer River: ClosedClosed
Skookum Drainage: ClosedClosed
Turnagain Pass: ClosedClosed November 21 due to inadequate snow conditions. #hopeforsnow
Twentymile: ClosedClosed
Seward District
Carter Lake: ClosedClosed
Lost Lake Trail: ClosedClosed
Primrose Trail: ClosedClosed
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClosed
South Fork Snow River Corridor: ClosedClosed
Summit Lake: ClosedClosed

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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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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