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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Monday, April 10th 2017
Created: Apr 10th 6:11 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.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

The avalanche danger is expected to increase to CONSIDERABLE above 1000’ due to spring time warming. Human triggered avalanches 2-6+ feet deep will become more likely in the afternoon on slopes steeper than 35 degrees that haven’t avalanche already. Triggering a wet loose avalanche or cornice will also be more likely in the afternoon. 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

The snowpack is in a tricky stage right now following a 10-day spring storm cycle that caused widespread avalanche activity throughout our region. On Friday and Saturday there were several human triggered avalanches in the Seattle Creek area that were large enough to kill or cause serious injury. Details about these incidents remain unclear, but it appears that folks got really lucky! Saturday afternoon’s sunny skies and warm temperatures also caused two large natural avalanches on Southerly aspects. One in Portage that ran over 3000’ vertical feet and a second avalanche on Pete’s South that triggered a wet avalanche in the mid elevations. 

There are several weak layers within our snowpack, the most noteable a reactive and widespread layer of buried surface hoar. There are also varying amounts of snow sitting on these weak layers throughout our region and slab depths range from 2-6+’ thick with Portage and Placer Valley on the deeper side. To complicate the situation spring time conditions and daily warming in the afternoon will increase the likelihood of triggering. This includes shaded slopes with drier snow. Yesterday's ridgetop winds (10-20mph) helped keep the surface cooler in the Alpine, but today this may not be the case. As we move away from the storm that created our current snowpack, slabs will become harder to trigger and it may not be the first person on the slope. Ease into terrain and avoid terrain traps. Follow safe travel protocols and pay attention to other parties in the area. Obvious clues like whumpfing, shooting cracks, and recent avalanches may not be present.

Location 1st Bowl - The looker left avalanche was reported as a human triggered avalanche and the lookers right slides may be natural or remotely triggered. Photo credit: Eddy Monteil

 

Buried surfad hoar found in multiple locations on Sunburst on Saturday and was reactive

 


Secondary Concern

Last weeks storm caused widespread wet avalanche activity due to above freezing temperatures and rain below 2700’. Now that the storm has passed and we are in a melt/freeze cycle of sorts - solar heating during the day and overnight cooling are the biggest factors that play into the possibility of wet avalanche activity. Last night temperatures hovered around 31F and cloud cover may have trapped some of the day time heat. This may allow today’s solar heating to melt surface crusts a little quicker than the past few days. Temperatures are forecasted to rise into 40F’s, but may reach the 50F’s near sea level. This means solar heating is certain, either through thin clouds or direct sun light. In the morning with freezing temperatures, the snowpack will be more stable, but as this crust starts to degrade in the afternoon, this is when human triggered wet loose avalanches will become likely on Southerly slopes steeper than 35 degrees. 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 changing surface conditions if you start sinking into wet snow on your skis or snowmachine avoid steep slopes.

Roller balls on a South aspect of Tincan and storm triggered slabs in the lower elevations from the end of a 10 day storm cycle. 


Additional Concern

Strong winds throughout the storm cycle combined with heavy snow have created large cornices overhanging leeward slopes. Daytime warming and solar heating will be adding stress to Cornices. Avoid travel on or underneath these backcountry bombs and remember that they often break further back on a ridge than expected. Triggering a cornice has the potential to initiate a large avalanche on the slope below. 

 


Mountain Weather

Yesterday was a mix of showery weather and partial clearing. Light rain and snow was experienced intermittently through out the day as well as sun shining through patches of clouds. Ridge top winds were from the East, 10-20mph. Day time highs were in the low to mid 40F’s. Overnight there have been varying amounts of cloud cover and scattered showers, but temperatures have dipped slightly below freezing. 

A similar showery regime with a mix of clouds and patches of sun is expected. Day time highs may reach the upper 40F’s to low 50F’s near sea level. Scattered snow/rain showers are possible today with up to an 1” of snow in the alpine (0.1” of rain.) Rain/snow line is expected to be around 1600’. Light ridge top winds are expected to diminish to calm conditions. Overnight lows should dip below freezing again tonight. 

Tomorrow isolated showers are expected, and skies may start to clear by late Tuesday evening into Wed as high pressure settles over Southcentral, AK. Diurnal daily temps swings could range from 25F to mid 50F’s this week. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 36  rain  0.1  73
Summit Lake (1400') 33  25 
Alyeska Mid (1700') 33  trace  0.07  67 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  ENE  26 
Seattle Ridge(2400') 26  ESE  11  24 

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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