CNFAIC LogoCNFAIC Logo

Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Wednesday, April 12th 2017
Created: Apr 12th 5:35 am
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.
 Show the Complete North American Avalanche Danger Scale
Hidden Creek B&B LLC
Special Announcement
  • Due to low snow cover, Twentymile drainage is now closed to snowmachines. You can check the status of riding areas at the bottom of this page.

The Bottom Line

The overall avalanche danger is MODERATE at all elevations. There are two main avalanche problems to deal with: 1) The possibility remains for triggering a large and dangerous deep slab avalanche (3-6' deep) on slopes over 35 degrees. Most likely slopes are those above 1,500' with a Northerly aspect and harboring cold dry snow. 2) A very warm day is on tap and wet snow avalanches are possible, and may even be likely, this afternoon. These could be wet slab avalanches and/or wet loose avalanches on Southerly aspects as well as all aspects below 1,500'. The danger could rise to CONSIDERABLE in shallow snowpack zones where wet snow avalanches may occur naturally.

Hiking in Portage Valley and on summer trails around the Advisory area (including the Turnagain Arm Trail a.k.a the bike path).  Extra caution is advised during the afternoon and evening hours for triails that cross under avalanche paths. Avalanches are still possible at the higher elevations that could send debris over snow-free hiking trails.

Summit Lake:  See the Saturday Summit Summary HERE and observations from the last few days HERE.

 


Primary Concern

With long days and sunny weather ahead, many folks may be thinking about summertime activities - however, winter is still alive in the mountains. Dry settled powder covers aspects on the North side of the compass at the mid and upper elevations and these zones are the exact places we are concerned about deep slab avalanches. A layer of buried surface hoar exists anywhere from 2-6' below the surface and is still producing concerning stability test results. This layer was also the culprit weak layer in many human triggered deep slab avalanches over last weekend. This problem is one of low probability but high consequence as these are large and potentially unsurvivable slides. Over time, the likelihood decreses but has not gone away - by any means. Points to think about if you are getting out this week:

  • Because the weak layer is deep, it is tough to effect and therefore tough to trigger. It will take someone hitting a 'thin spot' in the slab, often where rocks sit just under the surface, or a large trigger such as a snowmachine and/or groups of people.
  • These slides can be triggered remotely, for example, from a ridge or bench on the top/side or below. 
  • There may be no signs of instability before the slope shatters 
  • Several tracks may be on a slope before it releases

If wishing not to roll the dice on this deep slab possibility, one can always stick to slopes under 35 degrees on these shaded aspects with nothing steeper above you.


Photo: Deep slab avalanches that were believed to be snowmachine triggered several days ago on April 7th or 8th in Main Bowl/1st Bowl of Seattle Creek. Older photo, but this gives an idea of the deep slab avalanche issue we are dealing with. Crown heights are 3-6 feet. 

 

 If you haven't seen it yet, this video shows a snowpack stability test at a thin spot in the slab - likely trigger point. This test was done near a sub-ridge where slabs often are thinner due to scouring during storms.

-


Secondary Concern

As the day warms up - into the 50'sF in the parking lots possibly - expect the Southerly aspects and lower elevation snowpack to become so wet and saturated it is unsupportable to snowmachines, skis or boots. When the pack gets this loose then it's time to head to a different aspect as slopes steep enough to slide become suspect for wet snow avalanches. Human triggered wet loose slides and wet slabs are a possibility late in the day and nothing to mess with.

Springtime melt-freeze cycle (Southerly aspects): We are moving into what we call a melt-freeze cycle. Low avalanche danger in the morning, Moderate to Considerable danger in the afternoon. When the snowpack is frozen in the morning from nighttime cooling, it's stable. During the course of the day the pack warms to the point it is punchy and unsupportable, this is when the avalanche danger rises with the chance for wet snow avalanches. Wet avalanches can be small to very large. For today, keep an eye on Southerly slopes and see if any new wet loose avalanches release from under rocks or other dark features.  


Mountain Weather

Sunny skies and very light Westerly winds were over the region yesterday. Temperatures were warm - between 45-50F at 1,000' and below, along ridgelines in the 30-35F range. During the past 24-hours ridgetop winds have been 0-10 mph from the West.

Overnight, clear skies have dropped lower elevation and valley bottom temperatures into the 20'sF while upper elevations have remained warm (~30F) due to a warmer air mass that has moved in. Today, temperatures should climb rapidly to near 50+F with direct sunshine in the lower elevations while ridgetops cloud push into the 35-40F range. Skies should remain blue and ridgetop winds light, in the 5-10mph range from the Northwest with some stronger gusts on the peaks. This could be the warmest day of the season.

Long, warm and sunny days look to be in our future until Friday.  

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 35  71 
Summit Lake (1400') 36  24 
Alyeska Mid (1700') 37  66 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 29  12 
Seattle Ridge(2400') 33  NW  19 

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: Apr 11, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: OpenWide swaths of open river in the Placer Valley. Travel with extreme caution!
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: ClosedClosed for the remainder of the 2017 season.
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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