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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, March 14th 2018 4:37 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger is CONSIDERABLE. 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. Cautious route finding and conservative decision-making are essential. If the sun comes out today natural avalanches are possible, especially on southerly and easterly slopes. Pay attention to changing conditions.

A skier remotely triggered an avalanche on the skin track in Summit Lake Monday - see Saturday's Summit snowpack and avalanche summary and recent observations 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.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

There will be intermittent traffic delays Wednesday March 14, 2018 on the Seward Highway for avalanche hazard reduction work. Near mileposts 100 to 95, Bird Flats. Motorists should expect delays of up to 45 minutes between 10:00 AM and 2:00 PM. Updates will be posted on the 511 system.  http://511.alaska.gov/

 


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

What happens when you mix rapid warming and buried weak layers??? March Madness? Welcome to spring...Yesterday was an interesting day for avalanches. The sun came out, temperatures rose (some weather stations recorded temperatures into the 40Fs), high clouds came in and the heat was trapped. This "greenhousing" is believed to have been the cause of a natural avalanche cycle that started mid day and peaked around 5 pm. The highlight of this was a large natural slab avalanche that was observed on an NE aspect of Skookum. This appears to have run on the mid January facet/crust combination that has been a layer of concern in mid elevation terrain. This layer seems to be the culprit in the majority of the avalanche activity since last week's storm. What does this mean for today? We know that there is a slab approximately 2-4 feet thick over persistent weak layers that have been well documented and that are widespread across our regionLarge avalanches can be triggered by the weight of a skier or snowmachiner, especially in a thinner spot near rocks or ridges. There were avalanches triggered on Monday. If the sun comes out today there is the potential that a similar warm up may happen and naturals will be possible. It is important to recognize that the snowpack can be even more unstable as warm air and solar radiation affect cold snow and buried weak layers. Extra caution is advised.

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

  • Several feet of new snow fell last week on buried weak layers. There is poor snowpack structure. If triggered avalanches could be large and very dangerous.
  • If the skies clear pay attention to changing conditions. Solar radiation and warm air temperatures can quickly make the snowpack more unstable. Natural avalanches will be possible. 
  • 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. Evaluate the consequences if the slope releases; where will the debris go?
  • Realize you may not see signs of instability before the slope releases. 

Natural slab avalanche in Skookum that released around 5 pm.

Natural slab on Seattle Ridge that releases around 1 pm.

 Crown of one of the skier triggered Sunburst avalanches that occcurred Monday. 

 Mid elevation layer of concern: buried facets over a melt freeze crust. 


Avalanche Problem 2

Wet Loose

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Solar radiation and warm temperatures yesterday caused widespread wet loose avalanches. Some of these also triggered slabs on Southerly and Easterly slopes. If the sun comes out today pay attention to changing conditions. Naturals may run and could surprise you in the wrong spot. Wet loose avalanches may also be triggered from your skis or snowmachine in steep terrain on the solar aspects. 

Natural wet loose avalanches and a slab avalanche on Seattle Ridge yesterday


Additional Concern

Cornice

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.

Wind slabs: Shallow wind slabs formed on some leeward features Monday 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. 


Mountain Weather

Yesterday skies cleared earlier than forecasted and the sun came out. High clouds built in the afternoon.Temperatures rose into the low 30Fs to mid 40Fs. Winds were Easterly 5-15 mph gusting into the 30s. Skies became cloudy overnight and temperatures dropped into the 20Fs and low 30Fs. Winds shifted to the west and were light.

Today will be mostly cloudy in the morning but could become sunny in the afternoon. There is a chance of snow showers in the morning. Winds are forecast to be light and Northwesterly. Temperatures will be in the 20Fs to high 30Fs. Tonight will be mostly cloudy with temperatures in the 20Fs to low 30Fs and calm winds.

Tomorrow the next system approaches form the Southwest bringing snow showers in the afternoon and increasing winds. Snow is in the forecast into Friday. Stay tuned for snow amounts. The NWS described a persistent unsettled pattern continuing into next week. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  35 87 
Summit Lake (1400')  30  0    35  
Alyeska Mid (1700')   34   1    .11   79  

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  25 E-W  34 
Seattle Ridge(2400')   29   E 10   32  

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 20, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of April 20
Placer River: ClosedClosed as of April 17th
Skookum Drainage: ClosedClosed as of April 1st.
Turnagain Pass: Open
Twentymile: ClosedClosed as of April 13th
Seward District
Carter Lake: Open
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: Open
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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