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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Monday, March 13th 2017
Created: Mar 13th 6:24 am
1 Low Alpine / Above 2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

LOW avalanche danger remains in the backcountry at all elevations. Although triggering an avalanche is unlikely, it is not impossible on steep wind loaded features and in extreme terrain. Surface warming on East-through-Southwest-facing slopes due to radiation from the sun could make triggering an old wind slab or wet loose avalanche possible in the afternoon.  Be aware of old hard wind slabs and dry sluff in steep terrain, as well as large cornices. Glide cracks continue to open - limiting exposure under these is recommended.

Good travel habits remain important, even during 'green light conditions'. This includes exposing only one person at a time on a slope, watching your partners closely and having an escape route planned in case the snow moves. 

Summit Lake, South of Johnson Pass and North (in parts of the Girdwood Valley):  A reminder that the snowpack remains thinner in these areas with a poor structure. There is still a chance for triggering an avalanche deeper in the snowpack in these areas. Read the Saturday Summit Summary HERE.


Primary Concern

We have seen 19 days without any precipitation and eight days since a wind event impacted our region. Although the snowpack is pretty tired, a hard wind slab 12-18” deep was triggered by a snowmachiner two days ago on a SE aspect of Seattle Ridge. This is a good example of a wind loaded terrain feature still harboring unstable snow. Its also possible the sun and daily warming helped tip the balance. As you travel today, monitor the snow for damp or wet surfaces or new roller ball activity near rocks. These are obvious clues that the sun is impacting the snowpack and may increase the potential for triggering an old wind slab or wet loose avalanche. Kicking off even a small wind slab or loose snow avalanche in steep terrain may have high consequences. Things to keep in mind if you are headed to the mountains today:

 Wind Slabs: Old and hard winds slabs are easy to find but for the most part they are locked into place. Smooth pillowed snow on steep features or in rocky areas will be the most suspect zones for someone to initiate an old wind slab. 

 Loose Snow Avalanches (Sluffs): Dry sluffs on steep slopes are probable and have been fast moving this week. And, as mentioned above, wet loose (or damp) sluffs, both natural and human triggered, may occur.

Glide Avalanches: Glide cracks continue to slowly open above popular terrain on Seattle Ridge and in other areas of the advisory area. These could release at any time, watch for these cracks and avoid being under them.

Cornices: Cornices may start to loosen with daily warming - as always, give these monsters a wide berth from above and limit exposure time traveling underneath.

Persistent Slabs and Deep Slabs: There are various weak layers in our thin snowpack. Buried surface hoar sits 1-3+' below the surface and faceted snow sits in the mid and base of the pack. These weak layers with varying degrees of strength are in a dormant stage due to plenty of time to adjust with a lack of changing weather. Although its unlikely, an avalanche breaking deeper in the pack isn't completely out of the question in Johnson Pass, Lynx Creek and part of Girdwood Valley. 

This hard wind slab was initiated by a snowmachine just below the trees, lookers left side of photo, while exiting the slide path. This was on a SE aspect of Seattle Ridge at 2400' in an area near 'God's Country'. Photo by Brian Bird.

 

Also note the numerous glide cracks along Seattle Ridge SE face. 

 


Mountain Weather

Yesterday skies were clear and sunny. Temperatures averaged in the teens F and increased into the low 20F’s mid day. At lower elevations there were a few hours where temperature reached the high 20F’s. Winds were light and variable. Overnight there was a few hours where Westerly ridge top winds were in the 10-15mph range.

Today a similar pattern is expected. Temperatures in the low teens F could reach the mid 20F’s this afternoon. Winds are expected to be between 5-15mph from the Northwest. Thin cloud cover is possible this afternoon into the evening. 

Outflow winds are forecasted for Southcentral Alaska over the next few days, but aren’t expected to impact Turnagain Pass. High pressure will continue to impact mainland Alaska, but a developing front in the Gulf may bring scattered snow flurries to our region by Wednesday. Expect temperatures to remain cold.  

*Seattle Weather Station tables and graphs were not recording temperature history as of this morning. The current tempature at 7am was 14F. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 13  60 
Summit Lake (1400')  10 28 
Alyeska Mid (1700') 18  56 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  13 NW  18 
Seattle Ridge(2400')  *n/a WNW  4 12 

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: Mar 28, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: OpenPlacer remains open but SKOOKUM DRAINAGE will close to motorized use on April 1st.
Skookum Drainage: OpenSKOOKUM DRAINAGE CLOSES TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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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