CNFAIC LogoCNFAIC Logo

Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Friday, April 7th 2017
Created: Apr 7th 5:36 am
4 High Alpine / Above 2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
4 High Treeline / 1,000'-2,500' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
 Show the Complete North American Avalanche Danger Scale
Kitchen Legal, LLC
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. Dangerous avalanche conditions are expected region wide including: Lost Lake, Hatcher Pass, and the Anchorage Front Range. With clearing skies and warm day time temperatures forecasted throughout the weekend, human triggered avalanches will be likely. 


The Bottom Line

The avalanche danger remains HIGH above 1000’ due to a very unstable snowpack in Turnagain Pass, Placer Valley and Girdwood. Human triggered avalanches 2-6+ feet deep are very likely today, and during the heat of the day natural avalanches will be likely. CONSIDERABLE avalanche danger exists below treeline where a natural avalanche from above could easily run. Travel is not recommended in avalanche terrain. If choosing to play in the flats today, steer well clear of gullies and the bottom of steep slopes as many avalanches have been running full track to valley floors. 

Hiking in Portage Valley:  Avalanches occurring at the higher elevations can send large amounts of debris into valley bottoms and cover snow-free hiking trails. Avoid trails that cross under avalanche paths such as Byron Glacier or portions of the Trail of Blue Ice.

Summit Lake: An active avalanche cycle has occurred in Summit Lake this week and travel in avalanche terrain is not recommended. Read the Saturday Summit Summary HERE and observations from the last few days HERE.


Primary Concern

Over the last 10 days, a widespread avalanche cycle has occurred due to heavy snowfall, rain and strong winds in Turnagain Pass, Girdwood, Placer Valley, Portage Valley and Summit Lake. Large natural avalanches have been releasing on all aspects, particularly in the mid-elevation band below about 2,500’ and showing potential to propagate across wide distances. Yesterday there was a report of a D5 avalanche in Portage Valley- this is the largest size avalanche on the destructive scale. Limited visibility has made it difficult to know the extent of the avalanche activity in the alpine elevation zone. A brief window yesterday on the Southern end of Turnagain Pass confirmed many avalanche paths are still in tact or have been re-loaded above 2500’. 

Yesterday and additional 0.6” H20 fell in Turnagain Pass and .91” in Girdwood combined with strong Easterly ridge top winds. Storm related wind slabs 2-4+’ thick are likely, but could step down into deeper layers 6+’ deep. At this point it doesn’t really matter what the weak layer is because this is not an avalanche problem to mess with or try and out-smart.  The snowpack will remain touchy and human triggered avalanches are very likely in the mid and upper elevations today. These could run long distances.  Travel in avalanche terrain is not recommended.  Avoidance will be your best way to manage this problem, until the snowpack has a chance to recover and we can take stock of what is left of our snowpack.  

How much load is on the old weak surface from March? Storm totals (March 27 - 6am April 7th):

  • Turnagain Pass:     6.0” of H2O, 60+" of snow at upper elevations
  • Girdwood Valley:    6.1” of H2O,  61+" of snow at upper elevations
  • Summit Lake:         1.5” of H2O,  15+" of snow at upper elevations  

Many of the SW aspects of Turnagain Pass still have areas that have not avalanched or have been reloaded. Lips South face is a good example and was activity being loaded by winds yesterday. 

Significant wind loading on was observed on the Southern end of Turnagain Pass where good visibility allowed for a good view into the upper elevations yesterday. North side of Lips where winds were actively loading West and South aspects. 

 


Secondary Concern

The balance has been tipped and avalanches this week have been observed stepping down into old weak layers. Dirty debris in places is indicative that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6' and running the entire length of a slide path.  Again, avoidance is key with this problem as a persistent slab avalanche in our current snowpack is not a survivable event.


East face of Seattle Ridge near the motorized lot. Natural avalanches this week have stepped down into deeper layers of the snowpack and in this case to the ground. 


Additional Concern

Widespread wet avalanches have occurred this week due above freezing temperatures and rain below 2500’. Yesterday morning temperatures cooled and an additional 2-10” of snow fell above 1000’. Overnight periods of clearing skies and temperatures around freezing have created an egg shell crust in the lower elevation band. This is the first sign of the snowpack is starting to stabilize in the lower elevations following a week and a half of rain. Today solar heating is anticipated, either through thin clouds or direct sun light. The heat from the sun could easily initiate wet loose avalanches in the new snow in the mid and upper elevations. In channeled terrain an avalanche from above could entrain wet snow in the lower elevations. Again it will be important to maintain a conservative distance from all runout zones and avoid all avalanche terrain, slopes steeper than 30 degrees.


Clean up crew along the Seward Hwy clears debris from the rail road tracks after avalanche mitigation work this week.


Mountain Weather

Yesterday 0.6” of H20 fell in Turngain Pass and 0.91” of H20 was recorded in Girdwood, an estimated 6-10" of snow fell in the upper elevations. Rain/snow line was around 1000’. Easterly ridge top winds were strong, averaging in the 30’s mph and gusts in the 50’s mph. At 1000’ temperatures reached the low to mid 40F’s during the middle of the day and dropped back down to freezing 32F overnight. Partially clearing skies was observed in the early evening in Girdwood Valley and on the Turnagain Pass webcams. Satellite imagery confirmed periods of clearing skies overnight.

Today scattered snow and rain showers are expected, with only a small amount of precip, up to 0.08” of H2O (1-3” of snow in the alpine.) Rain/snow line may be as high as 1000’ with daily warming expected to bring temps at this elevation into the high 30F's. Overnight temperatures are expected to dip below freezing at lower elevations. Easterly ridge top winds are expected to be moderate, 10-25mph, but could be stronger along Turnagain Arm. 

A similar pattern is expected throughout the weekend with scattered snow/rain showers and periods of clearing skies. Not much accumulation is expected. Daily temperatures swings should range from 25F-40F. Ridge top winds are expected to decrease by Saturday. 

*Seattle Ridge weather station only recored winds from 7am through 1pm on Thurs, April 6. 
PRECIPITATION 24-hour data (6am - 6am)

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 36  .6   79
Summit Lake (1400') 36  26 
Alyeska Mid (1700') 34  .91  71 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  ENE  25  55 
Seattle Ridge(2400') 27  *SE  *8  *48 

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

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.
FCNFAIC