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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Aleph Johnston-Bloom  
Wednesday, February 1st 2017
Created: Feb 1st 4:29 am
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.
 Show the Complete North American Avalanche Danger Scale
Rossignol
Special Announcement

Placer and Twenty Mile: Travel is extremely difficult right now due to recent rain, warm temperatures and overflow. This area will remain open in anticipation of forecasted cooler temps but travel is NOT currently recommended for novice riders.

                                                     Dangerous avalanche conditions persist in many areas outside of our advisory area, around Southcentral Alaska
                                                     including the Southern Kenai Mountains, Hatcher Pass and Anchorage Front Range

  • The final CNFAIC report on the snowmachine avalanche fatality in the Snug Harbor area on Saturday is available HERE.  We want to thank those involved for their willingness to share their experience for others to learn from. Our thoughts continue to be with the victim's family, friends and rescuers.
  • The Southern Kenai Mountains, including Seward, Snug Harbor and Lost Lake zones continue to have dangerous avalanche conditions. This region recieved another 1-2' of wet heavy snow over the last few days and large propagating deep slab avalanches (5+' thick) are possible on slopes over 35 degrees. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential.
  • Click HERE for the Hatcher Pass Avalanche Center advisory and HERE for recent snowpack observations.

 


The Bottom Line

The avalanche danger is MODERATE in the Turnagain Pass area. On slopes over 35 degrees and above ~1,000', it is possible to trigger a wind slab on wind loaded slopes and there is the possibility of triggering a large (2-3') persistent slab avalanche that breaks lower in the snowpack. In addition cornice falls are still a concern. Below 1,000' the danger is LOW.

Girdwood Valley: Persistent slab avalanches have the potential to be larger, over 3' thick, and break near the ground on weak faceted snow. 

Summit Lake: Dangerous human triggered slab avalanche conditions persist in the Summit Lake zone. Check out the Saturday Summit Summary HERE

**The probability of triggering one of these large slabs is decreasing but the consequences remain high. Be sure to carry your rescue gear and practice safe travel protocol - such as exposing one person at a time, grouping up in safe zones, having escape routes planned and watching your partners!  

 


Primary Concern

Active wind loading was observed yesterday and Easterly winds were in the 20s gusting into the 40s for most of the day.  Today wind slabs will be possible to trigger on steep wind loaded (both top and cross loaded) slopes. These may be 6" to 2' thick. It will be important to look for pillowed or drifted areas and watch for shooting cracks. These slabs may allow you get out onto them before they break. In some places fresh wind slabs are sitting on old wind slabs and more than one layer might be triggered. Avoid areas with hollow sounding snow. A skier on Monday found a cross-loaded pocket on Sunburst and triggered a small wind slab on a convex roll. 

Cross-loading. Photo: National Avalanche Center 

Cross loaded slopes Seattle Ridge 1.30.17

 


Secondary Concern

The January 26th warm storm event added 2-3' of snow to the upper elevations and rain at lower elevations. This event overloaded a variety of weak layers in the pre-existing snowpack and caused a widespread avalanche cycle in the region. The good news is the snowpack is showing signs of adjusting to the load, the bad news is that there is still potential to trigger a persistent slab avalanche if you find the wrong spot. This can make for difficult snowpack assessment as the weak layers of concern (depth hoar, facets and buried surface hoar) are lurking anywhere from 2-4+ feet below the surface. Thicker snowpacks, as found at on the North end of the Turnagain Pass had a stronger snowpack to begin with and this has been a big factor in the area beginning to adjust quicker. This is opposed to the persisting unstable snowpack found South of Turnagain Pass and in the Girdwood Valley. The other factor to consider is potentially different snowpack depths and structure on different aspects due to the multiple wind events stripping slopes and loading slopes. Generally speaking Southerly and Easterly slopes are thicker while Westerly and Northerly are thinner. The thinner aspects even on the Northern end of Turnagain Pass have a more suspect structure with slabs resting on more developed facets. As always pay attention to signs of instability i.e. cracking, collapsing (whumpfing) and recent avalanches but be aware that they may not be present with this type of avalanche concern. 

In general - this is a high consequence but low probability situation. If choosing to ride or ski the steeper terrain, we recommend using safe travel protocol, especially exposing one person at a time and grouping up in safe zones. If a large slab is triggered it may run further than expected and wrap around terrain features taking out mid-slope relative safe zones. Since the weak layers in question are fairly deep, it will likely take finding a thin spot in the slab or a big trigger to initiate an avalanche. 

Snow pit @ 2200' on the NW shoulder of Magnum. Stiff wind slab over weak faceted snow at the base of the snowpack.

 

 


Additional Concern

Give cornices wide berth, avoid travel on slopes below them and remember they can break farther back onto the ridge than expected.  If cornices do break and fall they could trigger an avalanche on the slope below.


Mountain Weather

Yesterday was cloudy and there was very light snow/rain showers on and off throughout the day (depending on location and elevation).  Easterly winds were in the 20s and gusted into the 40s. Temperatures were in the 30s below 1000' and mid to low 20s towards ridge tops. There was slight cooling overnight. 

There is a chance of snow showers this morning with an overall clearing trend forecasted for this afternoon into the evening. Temperatures will 20s at upper elevations and 30s at sea level. Winds will start easterly 5-15 mph and shift to the North and may bump up with the outflow this evening. The weather for the remainder of the week looks to be dominated by blocking pattern that will bring sunny skies and cooler temperatures into the weekend. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  32  trace  0 57 
Summit Lake (1400')  28  1  .1  25
Alyeska Mid (1700')  30  2  .1  51

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  21  ENE 22   47
Seattle Ridge(2400')  24  SE 15  30

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 15, 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: Open
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

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
© 2017 Chugach National Forest Avalanche Information Center. All rights reserved.
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