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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, March 12th 2018 5:40 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

CONSIDERABLE avalanche danger remains above 1000' on all aspects. Large slab avalanches 2-4 feet thick are likely to be triggered on slopes steeper than 30 degrees. These may be triggered from a distance or from the bottom of a slope. Additionally, moderate winds today may be forming shallow wind slabs and adding stress to the snowpack. Cautious route finding and conservative decision-making will be essential for safe backcountry travel.

MODERATE avalanche danger exists below 1000’ where triggering a large slab avalanche is possible in areas with avalanche terrain like Portage Valley and Placer Valley.

Natural avalanche activity was observed in Summit Lake area over the weekend - see Saturday's snowpack and avalanche summary and observations from yesterday HERE. 


 Show the Complete North American Avalanche Danger Scale
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.
Special Announcement

**Heightened avalanche conditions are being seen region-wide. Human triggered avalanche activity was reported in the South Fork of Eagle River on Saturday.


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a large and unmanageable slab avalanche 2-4' thick remains our primary concern.  Evidence of natural avalanches were seen yesterday near Silvertip and in Summit Lake. These avalanches likely occurred during a storm that ended Friday with strong winds and 2-4 feet of new snow across our region.  On Saturday, a snowmachiner remotely triggered two slabs on Seattle Ridge from a meadow below the slope, and a skier triggered a slab in Girdwood in the Notch Mtn area. These human triggered avalanches were in the mid elevation bands and on small steep terrain features. Due to poor visibility this weekend little information exists from the Alpine. What we do know is various layers of old faceted snow and buried surface hoar sit under 2-4 feet of storm snow from Friday. These persistent weak layers have been well documented and are wide spread across our region. 

Much uncertainty exists as to how our snowpack is adjusting to its new load,  and today’s moderate winds will be transporting 3-4 inches of loose surface snow. This is not quite enough wind to anticipate natural activity, but just enough to be adding additional stress to the snowpack where a human could tip the balance. 

If you are headed out into the backcountry today things to keep in mind are:

  • The mountains are still adjusting to the several feet of new snow that fell three days ago
  • Avalanches can be triggered from the flats or remotely from an adjacent slope - be extra cautious to avoid being in a runout zone 
  • Stick to slopes less than 30 degrees and ease into steeper terrain slowly - after careful snowpack assessment. Evaluate the consequences if the slope releases; where will the debris go?
  • Listen for whumpfing (collapsing) in the snowpack, an obvious clue that an avalanche could be triggered in steeper terrain

Recent natural avalanche activity on a heavily cross-loaded SE aspect between Silvertip and Moose Mountain. Be aware that the Southern end of Turnagain Pass and Summit Lake have a thinner and weaker snowpack. 

 

Stability tests yesterday in the mid elevation zone of Corn Biscuit showed propagation potential on a layer of buried surface hoar mixed with facets.

 

A Skier triggered avalanche from Saturday (lookers right side) at 2000’ on a NW aspect of Notch Mountain in Girdwood. No one was caught and the party reported that the slide on lookers left was there before they skied the slope and may have occurred naturally or was triggered remotely from above. 


Additional Concern

Wind Slabs

Wind slabs: Shallow wind slabs may be forming on leeward features today due to moderate Easterly winds in the Alpine. Triggering a wind slab will likely be shallow, but could step down to a deeper layer of the snowpack and create a much larger and more dangerous avalanche. 

Cornices: Cornices have grown and are suspect for breaking while traveling along ridgelines. Give these an extra wide berth and minimize any time below them. Cornice falls can trigger avalanches on slopes below.

Loose snow: Several inches of low-density snow fell this weekend, and moderate winds along ridges could initiate some loose-dry point releases (sluffs.) Radiation from the sun is not expected to be a factor today, but should we experience a period of clearing skies, small wet-loose sluffs are possible on Southerly aspects in steep rocky terrain. 


Mountain Weather

Yesterday was overcast becoming obscured in the afternoon by snow showers that dumped 4” of low density snow in Turnagain Pass and Girdwood. Light Northwest ridge top winds (5-15mph) increased overnight to 15-30mph from the Southeast. Temperatures ranged from the upper teens (F) to mid-20F’s. 

Ridgetop winds will remain moderate (10-30mph) from the East throughout the day and decreasing to Light by the evening. Scattered snow showers may bring an inch of new snow, but not a lot of accumulation. Skies are expected to be overcast, but patches of clearing skies may occur later in the day and overnight.  Daily temperatures may swing from the low-20F’s into the low-30F’s by mid-day.  

A showery and active pattern is expected to continue throughout the week with periods of snow flurries, but not much accumulation. Wednesday looks like the first chance for a partial clearing, but lots of uncertainty remains in our daily forecast on timing of several Lows passing through our region. Daily temperatures swings are expected to be in the low-20F’s to mid-30F’s and winds may range from Light to Moderate throughout the week. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 27  .2  93 
Summit Lake (1400') 23  .1  35 
Alyeska Mid (1700') 22  .2  83 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 18  E 32 
Seattle Ridge(2400') 22  n/a  n/a   n/a  

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 06, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20th
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: ClosedClosed as of May 7th. Happy summer, see ya when the snow flies!
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: ClosedClosed as of 4/27
Lost Lake Trail: ClosedClosed as of April 13th
Primrose Trail: ClosedClosed as of April 13th
Resurrection Pass Trail: ClosedClosed as of April 20th
Snug Harbor: ClosedClosed as of 4/27
South Fork Snow River Corridor: ClosedClosed as of April 13th
Summit Lake: ClosedClosed as of April 20th

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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