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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Sunday, April 9th 2017
Created: Apr 9th 5:08 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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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Special Announcement

Southcentral Alaska has been experiencing a widespread avalanche cycle over the last week due to warm temperatures, snow and rain, and strong winds and now SUN!!! Dangerous avalanche conditions are expected region wide including: Lost Lake, Hatcher Pass, and the Anchorage Front Range. Above freezing day time temperatures are forecasted throughout the weekend and human triggered avalanches will be likely. 


The Bottom Line

The avalanche danger  is CONSIDERABLE above 1000’ due to weak snow sitting under 2-6+ feet of storm snow in Turnagain Pass, Placer Valley and Girdwood. Human triggered avalanches 2-6+ feet deep are likely today on slopes that haven’t avalanched already. The likelihood of triggering will increase during the heat of the day and natural avalanches will be possible. Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. 

Below 1000' a MODERATE avalanche danger exists where triggering a wet avalanche will be possible during the heat of the day. Watch for changing conditions.

Hiking in Portage Valley and on summer trails around the Advisory area (including the Turnagain Arm Trail a.k.a the bike path). Avalanches occurring at the higher elevations in this last storm sent large amounts of debris into valley bottoms and covered snow-free hiking trails. Continue to avoid trails that cross under avalanche paths such as Byron Glacier or portions of the Trail of Blue Ice and Crow Pass. The Turnagain Arm Trail between Bird and Girdwood remains CLOSED for the winter.

Summit Lake: An active avalanche cycle has occurred in Summit Lake this week and ELEVATED CAUTION is advised. Read the Saturday Summit Summary HERE and observations from the last few days HERE.


Primary Concern

Yesterday we received reports of three seperate human triggered avalanches in Seattle Creek Zone, and possibly a fourth. These were large slab avalanches that likely failed on the March 28th buried surface hoar and/or the March facets. Incident details are unclear, but so far there have been no reports of anyone buried or injured. These were not small avalanches - they were all 3-6+ feet deep, maybe larger and propagated long distances. Bottom line an avalanche this size could be unsurvivable. There was also a very large Natural avalanche in Portage Valley yesterday. The Portage DOT web cam captured the debris in motion at the bottom of the avalanche path at 5:10pm.   

Test pits yesterday found easy propagation potential in reactive buried surface hoar on Sunburst. (See video below.) A 10-day storm cycle that ended Friday morning has left anywhere from 3 feet to 6+ feet (possible more in Portage/Placer/20 mile area) of snow in the upper elevations. Strong storm winds also created variable slab depths. This storm cycle came as rain in the lower elevations and produced a widespread large natural avalanches region wide. Slopes that didn’t slide during the storm are suspect. Slabs maybe slightly harder to trigger and it may not be the first person on the slope. Spring time conditions and daily warming in the afternoon will increase the likelihood of triggering.  Ease into terrain and avoid terrain traps. Follow safe travel protocols and pay attention to other parties in the area. Conservative decision-making is essential. Don't let the sunny weekend lure you into an accident. Be patient! 

Human triggered slab avalanche in 1st Bowl (aka Main Bowl) that occured yesterday (4/8/17.)  If anyone has more details or pictures of any of the Seattle Creek avalanches yesterday please submit an observation HERE. It's easy and can be done anonymously. Reporting near misses can help prevent future accidents and save lives!!! 

 

 

This natural avalanche happened yesterday in Portage Valley and 'debris in motion' was capture on the Portage DOT web cam.  

 

 


Secondary Concern

Widespread wet avalanches have occurred this week due above freezing temperatures and rain below 2700’. Yesterday there was a very large sun-triggered avalanche in Portage Valley and widespread roller ball activity and some wet loose avalanches on Southerly slopes. Mostly clear skies overnight and temperatures below freezing have created a solid crust in the lower elevation band. A sun crust also extends into the Alpine on solar aspects. Yesterday’s warm temperatures caused these crusts on steep Southerly aspects (both in the lower and upper elevations) to completely break down causing the snowpack to be wet and saturated. In the morning with freezing temperatures, the snowpack will be more stable, but as this crust starts to degrade, this is when human triggered avalanches will become likely on slopes steeper than 35 degrees. Temperatures are forecasted to rise into the mid 40Fs again today and solar heating is certain, either through thin clouds or direct sun light. In the afternoon, when the crust melts wet-loose avalanches will be possible. This daily warming will also increase the potential for triggering a deeper slab in drier layers in the alpine, on ALL ASPECTS! Pay attention to roller balls indicating surface warming and avoid slopes if you start sinking into wet snow on your skis or snowmachine. 

Wet avalanches that occured on Seattle Ridge during the 10 day storm cycle. Photo taken 4/5/17 

 


Additional Concern

Strong winds throughout the storm cycle combined with the heavy snow have created large cornices overhanging leeward slopes. Daily warming is also contributing to their instability. Yesterday there was a possible cornice triggered slab avalanche in Seattle Creek. Details are unconfirmed, but either way avoid travel on or underneath these backcountry bombs. They are likely to trigger a large avalanche on the slope below and often break further back on a ridge than expected.  


Mountain Weather

Yesterday was clear and sunny. Daily spring time temperature swings were between mid 20F’s in the morning reaching mid 40F’s by mid to late afternoon at sea level. In the upper elevations Sunburst wx station recorded above freezing temperatures between 1pm and 5pm with a high of 38F. Ridgetop winds were light (5-10mph) from the East and picked up later in the evening to 10-20mph. No precipitation was recorded. Overnight temperatures have dropped below freezing.

Today temperatures are expected to be in a similar range. Temps in the mid 20F’s this morning increasing to high 30F’s to mid 40F’s by the early afternoon. There is a chance for scattered snow/rain flurries today, with a possibility 1” of snow (0.1” of water.) Clear skies this morning could range from partly cloudy to cloudy this afternoon. Ridge top winds are expected to be in the 5-15mph from the SE today.

A similar spring time pattern is expected this week. No significant changes are in the immediate forecast. Expect clear skis to partly cloudy through midweek.  Diurnal daily temps swings could range from 25F to mid 40F’s this week. 

*Center Ridge Snotel site and Summit Lake Snotel sites stopped recording data from 9am to 10pm on 4/8/17.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') *n/a  *0  *0 *74
Summit Lake (1400') n/a  *0 *0 *26 
Alyeska Mid (1700') 35  68 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 28  22 
Seattle Ridge(2400') 28  SE  20 

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 08, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedRain and snow have fallen in Turnagain Pass this week, but not enough to open for snowmachining. Continue to check back to this site for updates.
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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