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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Thursday, April 6th 2017
Created: Apr 6th 6:20 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.
4 High Below Treeline / Below 1,000' Travel Advice: Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
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Special Announcement

Roof avalanches have been occurring over the past week in Girdwood due to warm temperatures and rain. Be aware that roofs will continue to shed today and into this coming week.

An avalanche near milepost 98.7 of the Seward Highway, caused damage to a Chugach Electric power line resuting in an overnight power outage between Potter Valley and Whittier. The pole is yet to be inspected due to additional overhead avalanche concerns but as of 6AM crews are in the process of restoring power to these communities via the Hope sub-station.  

There will be intermittent traffic delays Thursday April 6, 2017 on the Seward Highway for avalanche hazard reduction work. Avalanche Crews will be conducting hazard mitigation from mile post 90 to 100. Expect traffic delays up to 1 hour. Thursday (4/6/2017) 0900- 1200. Updates will be posted on the 511 system. http://511.alaska.gov/


The Bottom Line

HIGH avalanche danger persists today as another wave of wet, warm and windy weather impacts the advisory area.  Natural avalanches are likely and human-triggered avalanches are very likely.  TRAVEL IN AVALANCHE TERRAIN IS NOT RECOMMENDED. If choosing to play in the flats (and rain) 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:  Several natural avalanches observed yesterday.  Travel in avalanche terrain is not recommended. Read the Saturday Summit Summary HERE.


Primary Concern

For the past week, observations have been limited due to elevated avalanche danger and poor visibility.  A brief window into the alpine yesterday confirmed our suspicions that we are still within a very active natural wet avalanche cycle.  Temperatures were the warmest we’ve seen all spring at ridge top locations yesterday and the mountains surrounding Turnagain Pass appear to be going thru a spring ‘shed-cycle’ of sorts.  Large natural avalanches are failing on all aspects, particularly in the mid-elevation band below about 2,500’ and showing potential to propagate across wide distances.  What hasn’t avalanched yet will be stressed by another half inch of water weight today.  These could fail either as storm slabs (2-4’ deep) or step down into weaker snow near the ground (4-6+’ deep).  At this point it doesn’t really matter what the weak layer because this is not an avalanche problem to mess with or try and out-smart.  The snowpack will remain touchy and with natural avalanches likely again today, travel in avalanche terrain is not recommended.  Avoidance will be your best and only tactic until this warm and wet pattern of storms subsides and we can take stock of what is left of our snowpack.  

 Nearly wall to wall avalanching on Seattle ridge (lookers left of the common snowmachine up-track) "Repeat offender" path as viewed from the Seward Highway.

WIND SLABS and CORNICES:

Strong winds last night combined with more snow will act to create large wind slabs and cornices on leeward slopes in the upper elevations.  With temperatures rising to above freezing in the alpine these may release naturally and could entrain enough snow to run quite far. Any additional wind and precipitation today will add further stress.

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

Turnagain Pass:     4.7" of H2O, 48+" of snow at upper elevations
Girdwood Valley:    5.5" of H2O,  55+" of snow at upper elevations
Summit Lake:         1.6" of H2O,  15+" of snow at upper elevations   

Widespread avalanching on Eddie's lower rolls as seen from the RWIS web cam during a brief period of clearing yesterday afternoon.


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.

Recent full-depth avalanche on Seattle ridge (across from Sunburst) stripping out the entirety of our snowpack. 


Mountain Weather

Daylight hours yesterday provided a brief reprieve from the deluge of wet, cloudy weather (enough to view the alpine) though we still ended the 24-hour period with .5 - .7” of water and likely another 5 – 10” of snow above the freezing line (~2,000’).  Temperatures were WARM with the Center ridge SNOTEL topping out at 44 degrees (1,880’) and Sunburst weather station (3,800’) reaching a high of 30 degrees.  Overnight, another front impacted our area with temperatures dipping slightly and east winds increasing quite dramatically around 6pm with Sunburst measuring a 7-hour period of sustained winds in the 40’s and gusting into the 70’s mph from the east.

You guessed it, another storm day on tap for our region today!  Temps should cool slightly (mid-30’s at 1,000’) from yesterday bringing the rain/ snow line back down somewhere closer to 1,500’.  Expect another .5” of water and winds again from the east in the 20 – 45mph range at ridge top level. 

Looking out toward the weekend we may see a break in this overall pattern and see some clearing with slightly cooler temperatures by Saturday and Sunday.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  40  0 .7  79 
Summit Lake (1400') 38   0  .1 27 
Alyeska Mid (1700')  35  0  .5  72

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  27 26   74
Seattle Ridge(2400')  30  32* 75* 

*Winds reporting since 3pm

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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