CNFAIC LogoCNFAIC Logo

Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, April 19th 2018 5:29 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
Previous ForecastNext Forecast
BROUGHT TO YOU BY
The Bottom Line

New snow and wind over the past 24-hours has kept the avalanche danger MODERATE. Watch for new storm slab and wind slab avalanches above 2,500' where up to a foot of new snow may be found. Below this, human triggered wet avalanches are possible on steep slopes with a rain soaked snowpack. 

Portage Valley:  A CONSIDERABLE avalanche danger exists where over a foot of snow has fallen at the higher elevations and an inch of rain below. Natural dry snow avalanches are possible along ridgelines and wet snow avalanches below. *Remember there are avalanche paths that can run over popular hiking areas such as Byron Glacier trail.  

FRIDAY AVALANCHE OUTLOOK:
No avalanche forecast will be issued tomorrow, Friday April 20th. Similar avalanche conditions are expected. 
Pay attention to how much new snow exists and if it is bonding to the crusts underneath. Also, watch for warming, resulting in wet loose avalanches composed of the new snow. 


 Show the Complete North American Avalanche Danger Scale
2 Moderate Alpine / Above 2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
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
  • CNFAIC is transitioning to springtime hours in preparation for the end of the season. We are issuing forecasts 4 days/wk on Sat, Sun, Tue, Thur. The final forecast will be on April 26th with our springtime tips report on April 28th. 

Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Human triggered fresh storm slabs or wind slabs 6" to a foot or more thick are our main concerns today and tomorrow. We are in the midst of a springtime stormy weather pattern. Light rain has been falling at the lower elevations and snow above this. The rain/snow line has been fluctuating between 1,000-2,000', in general. Strong Easterly winds accompanied the peak of the precipitation, which was yesterday afternoon.

Estimated Storm Totals from Tuesday night through 6am Thursday:

Girdwood Valley:  ~4-8" snow above 2,500'
Portage Valley:     ~1-2' snow above 2,500'  (by far the winner, areas closest to the Sound are the most favored for precip amounts)
Turnagain Pass:   ~6-10" snow above 2,500'
Summit Lake:       0" to a trace 
 

If you are headed out to catch the new snow at the higher elevations, caution is warranted. The new snow is falling on hard sun crusts on East, South and West aspects and on facets over a crust on high North aspects. Initial bonding should be poor in areas receiving over ~8" of new snow. Keep in mind, wind drifted snow could form wind slabs as thick as a foot or two. This makes small avalanches much larger quickly. This hazard is a direct result of how much snow has fallen, if you only find a few inches of new snow, it's not enough for a storm slab but watch for pockets of wind drifted snow on steep slopes.

 

PRE-STORM SURFACE - NORTHERLY ASPECT:  1cm of loose dry snow existed on hard melt/freeze crusts above 2500' on shaded aspects

 

PRE-STORM:  Slick melt-freeze surfaces on the South end of Turnagain Pass (Lynx Creek last week).
 


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Light rain has been falling on an already saturated snowpack below 1,000' and up to 2,000' in places. Wet loose avalanches, and even a wet slab, are possible on any steep slope with a wet, soupy and non-cohesive snowpack. 

These wet avalanches are most likely to threaten people that venture under avalanche terrain at the low elevations, such as in Portage Valley along the edges of Portage Lake and the Byron Glacier trail. 


Additional Concern

Cornice

Cornices are starting to fall. New growth from the recent snow and wind on already teetering cornices will only add to their instability. Give them plenty of space and limit exposure time underneath. 

Recent cornice fall and subsequent slab avalanche triggered below in the Skookum drainage last week before the wet weather.

 
-


Mountain Weather

Yesterday, cloudy and wet weather was over the region. Light rain fell in Girdwood and Turnagain Pass (~.1-.4") and heavier rain in Portage (1"). The rain/snow line fluctuated between 1,000-2,000' and above this anywhere from 3-10+" could be found depending on favored zones mentioned above. Ridgetop winds during the peak of the storm were 20-30mph with gusts to 68 from the East. Winds have died off early this morning and sit in the 10-15mph range. Temperatures have been in the 40'sF at sea level and in the mid to lower 20's along ridgelines. 

Today, cloudy skies and light rain below 2,500' is expected while a trace of snow may fall above this. Ridgetop winds will remain Easterly in the 10-15mph range. Temperatures should warm to 40F at 1,000' and remain in the 20's along ridgelines. 

For tomorrow and even into the weekend, the active pattern we are in will continue. Cloudy skies, light rain, gusty Easterly gap winds along Turnagain Arm and incremental snow accumulation above 2,500'. Again, favored precipitation areas are those closest to the coast such as Whittier. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 33  .3  68 
Summit Lake (1400') 35   0 22 
Alyeska Mid (1700') 34  0.15  61 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 23  NE  23  51 
Seattle Ridge(2400') 28  12  31 

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
© 2018 Chugach National Forest Avalanche Information Center. All rights reserved.
FCNFAIC