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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Saturday, January 2nd 2016
Created: Jan 2nd 6:58 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
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The Bottom Line

Up to 2 feet of new snow and strong wind overnight has rapidly loaded the mountains surrounding Turnagain Pass and created a HIGH avalanche danger in the Alpine zones (above 2,500'). A CONSIDERABLE avalanche danger exists at Treeline (1,000'-2,500'). Natural wind slab avalanches, 2-6' thick likely occurred overnight and are possible through the day today. Human triggered avalanches are likely on steep wind-loaded slopes. Sticking to mellow terrain (off and out from under slopes 35 degrees and steeper) and avoiding avalanche terrain is recommended in Alpine zones. In the Treeline zones, careful snowpack assessment and conservative route-finding will be necessary. A MODERATE danger exists in runout zones below 1,000' where debris from a slide releasing above may reach.

Don't forget to check the weekly summary for Summit Lake (on the Kenai). This summary is produced on Saturday mornings at 7am.

OUTSIDE OF CNFAIC ADVISORY ZONE:

*Photo below is of a large wind slab avalanche on Flattop Mountain, just above the Glen Alps parking lot in Anchorage (credit: Bob Lohr). This is thought to have slid on Dec 31st, with debris crossing the summer trail. Strong winds and snowfall are creating dangerous avalanche conditions throughout the region. More details on this slide can be found HERE as well as a large human triggered wind slab in the Eagle River area, HERE. Keep in mind summer trails can pass through avalanche paths such as the Flattop trail, as well as year around trails such as the Powerline trail.

 

If you are thinking of heading North today to Hatcher Pass - be sure to check out their Saturday morning advisory at hatcherpassavalanchecenter.org


Primary Concern

Another day, another storm. Since the last dry spell, just before Christmas and during the Solstice, we have seen roughly 8 feet of snow fall above treeline (a rain/snow combo below this). During this time we have also seen alders continue to be laid over and covered up, terrain features smoothed out and, as of today, a 13 minute gain of daylight. Just overnight, another intense pulse of moisture added 20+" of dense snow at treeline on Turnagain Pass with a rain/snow line around 800'. Precipitation and wind has abated this morning, yet the avalanche conditions remain dangerous.

If you are thinking of heading to Turnagain Pass today, keep in mind the mountains have just received a 'rapid loading' event. Not only is 20+" of new snow loading slopes (2.5" of water equivalent), but very strong Easterly winds have loaded leeward slopes and cross-loaded gullies. Wind slabs in the new snow could be as thick as 6' in places. 

Many different avalanches are possible today:

1) Wind slab: Triggering a wind slab 2-6’ thick is likely on steep wind loaded slopes. Winds are forecast to remain from the East in the 20-30mph range. If this is the case, fresh and sensitive wind slabs will remain through the day. 

2) Cornices: With such strong winds and warm snow at the ridgetops, we can expect cornices to be tender! Not only can these trigger an avalanche below, but may also trigger a slide breaking deeper in the snowpack - creating a very large avalanche. 

3) Wet loose avalanches: More rain on snow will saturate the upper layers of the snowpack below 1500’. This is more of a concern in areas with terrain traps and in steep channeled terrain where an avalanche from above will be impossible to escape. 

Yesterday's field day, just prior to the heavy snowfall, showed the December storm snow bonding well at the mid-elevations. Keep in mind as you watch the video that another 20+" of snow has fallen.


Secondary Concern

As mentioned in the video above, sitting under 5-7' of settled storm snow sits an old layer of faceted snow above the Thanksgiving Rain Crust (TRC). This layer extends to around 3,000' and continues to be on our radar. Over the past several days, we have had reports of avalanches breaking into older weak snow, this is primarily in the periphery of our advisory area such as Summit Lake and Girdwood Valley. As the snowpack gets yet another load, we will be monitoring whether slides are breaking in older/weaker snow.


Mountain Weather

Obscured skies and strong Easterly winds were over the area yesterday. Light snow fell above 1,500' while rain fell below 1,400'. Beginning yesterday evening, snowfall increased and the rain/snow line dropped to ~800' at Turnagain Pass. Overnight, we have seen over 2" of water equivalent from Girdwood to Turnagain Pass. 

As of this morning, the main 'fire hose' of sub-tropical moisture has moved off to the East, yet strong Easterly winds and light snowfall will remain today. The rain/snow line should remain just below 1,000' and we could see another 2-5" of snow at the mid-elevations. Winds are forecast to average in the 20-30mph range from a generally East direction. Temperatures will remain in the mid 20's F on the ridgetops and the low 30'sF at 1,000'.

This warm and stormy pattern looks to be over us through Monday with a possible break between storm Tues/Wed.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31  20  2.5  89 
Summit Lake (1400') 33  0.8  26 
Alyeska Mid (1700') 32  9 (very wet snow) 2.2  64 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 24  ENE  41  99 
Seattle Ridge(2400') 27  N/A  N/A   N/A  

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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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