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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Friday, April 10th 2015
Created: Apr 10th 6:31 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
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.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
Alyeska Pipeline Service Company
Special Announcement

Beginning next week, we will be issuing advisories 5 days a week.  Advisories will be posted at 7 am on all days of the week except Mondays and Wednesdays.  The final advisory of the season will be posted on Thursday April 30th.


The Bottom Line

The danger is CONSIDERABLE in the Alpine.  Slabs 2-3’ thick will be sensitive to human triggers and could release naturally with daytime warming and occasional sunshine on all aspects.  These slabs have the potential to step down to layers buried more deeply on North aspects and be in the 3-5’ range.  

The danger is MODERATE in the Treeline elevations, where slabs in the 1’ range will be sensitive to human triggers on steep wind loaded slopes.

Loose snow avalanches, both dry and wet, will be likely on steep slopes at all elevations.  Cornices will also be sensitive and are yet another reason for conservative decision making today.

Significant loading over the past 24 hours has created unstable conditions.  Because of this it will be critical to avoid slopes over 35º steep in the Alpine.  Avoidance of runout zones when traveling in the mid elevations will also be necessary as avalanches have the potential to be high in volume and run through multiple elevation bands.


Primary Concern

Snowfall that was intense at times yesterday has created slabs that will be tender today.  Slab depths will range anywhere from a few inches to 2 feet thick.  In the Alpine these slabs sit on a slick crust on South facing slopes and a variety of surfaces on North aspects.  Regardless of what these slabs are sitting on, they are dense, thick and very sensitive to human triggers.  Brief periods of sunshine will increase their sensitivity today.  While we found the new snow well bonded to underlying surfaces in our limited observations yesterday, all slopes 35º and steeper should be treated with suspicion today.  These slabs will be thickest, over 2 feet, where they have a wind component, and be found on leeward slopes around Turnagain Pass.

Cornices have been growing steadily over the last week.  Yesterday was no exception.  Expect cornices to be very sensitive today.  Give these behemoths a very wide berth along ridgelines and avoid traveling underneath.

Conservative terrain selection will be key today, as rapid loading over the past 24 hours has created unstable conditions.  Avoidance of terrain 35º and over and being in the runout of terrain from above will be critical.


Secondary Concern

The majority of slab activity should be in the 2-3’ range today.  However, there is potential for slabs to step down into more deeply buried weak layers, especially on North facing slopes in the Alpine.  These layers are anywhere from 3-5’ down.  Should avalanches step down into these layers expect volume to be very large and high enough to make consequences of being caught very high.  This is not an issue to be taken lightly.  A significant load has been put onto these layers and it will take time for those layers to adjust. 

Travel advice around this issue is simple for today: avoid North facing slopes in the Alpine.


Additional Concern

Both dry and wet loose avalanches are likely on steep slopes today at all elevations today.  Snow below the recent storm slabs was wet yesterday in the lower elevations.  Because of this, the potential for higher volume wet loose avalanches exists in the lower elevations and will be more likely during daytime heating and sunshine today.  Volume will generally be medium to high and will increase on sustained slopes that allow for entrainment.


Mountain Weather

Yesterday brought significant snow, wind and mild temps to the area.  Snowfall totals over the last 24 hours:
Turnagain SNOTEL: 18” snow/1.4” H20
Alyeska Mid: 8” snow/.8” H20
Summit Lake: 1" snow/.1" H20
Rain/snow line was around the 500’ mark for most of the day.  Winds were moderate out of the East.

Today expect lingering snow showers and cloudy skies as a large area of low pressure continues to spin in the Gulf of Alaska.  Snowfall amounts will be light, in the 1-2” range.  Ridgetop winds will be out of the East at 5-10 mph.  Temperatures at 1,000’ will climb into the mid 30s F.

The extended outlook is showing a very gradual change though the weekend.  Expect clouds and showery conditions to linger as low pressure in the Gulf slowly moves East.

*Seattle ridge wind sensor is rimed.  Average is 6am-4am.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29 18 1.4 77
Summit Lake (1400') 33 1 .1 12
Alyeska Mid (1700') 31 8 .8 48

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21 ENE 27 58
Seattle Ridge(2400') 25 * 13* 50*

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 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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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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