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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Saturday, February 14th 2015
Created: Feb 14th 6:36 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'
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The Bottom Line

The avalanche danger is CONSIDERABLE today in the Alpine on steep wind loaded slopes.  Freshly formed slabs up to 12” thick will be easy to trigger and could release naturally.  The danger is MODERATE on non wind loaded slopes in the Alpine and in the Treeline elevations, where pockets of shallow slab ranging from 4-8” thick could be triggered on steep slopes.  Wet loose avalanches are also an issue to contend with today in the lower elevations where warm temperatures and occasional rain will weaken the snow surface.


Primary Concern

Snow does not like rapid change.  When rapid change occurs, weak layers have a hard time adjusting to the load.  Winds overnight have brought about this rapid change.  Slabs have been actively growing on leeward slopes in the higher elevations.  Winds have been mainly out of the East.  The important thing to remember about wind is that direction changes are common in mountainous terrain.  With that said, recognition of wind loaded slopes is a better assessment tool than reading the weather station data when it comes to wind direction and loading patterns.

Shooting cracks and collapsing are obvious indicators of unstable slabs.  Stiff, hollow and upside snow should be avoided today in leeward starting zones and cross loaded terrain features.  These slabs could build into the 12” range and have enough volume to injure or bury a person.


Secondary Concern

A layer of weak faceted snow sits anywhere from 2-16” below the surface.  This layer is widespread throughout the forecast area.  This layer is deepest on the North end of Turnagain Pass (Eddies, Pyramid) where snowfall earlier in the week put down slabs up to 12” thick.  Heading South along the Pass that slab gradually gets thinner and less continuous across slopes with averages in the 6-8” range.  As a result we have seen more reactive snow where that slab is thicker, including remotely triggered avalanches within the last 2 days.  In the Girdwood Valley we have a different setup, where older dense wind slabs 4-8” thick that formed a week ago are sitting on this weak layer and concealed by 6" of snow that has fallen this week.  

To put it simply, we have the perfect recipe for a slab avalanche in many areas today; slab + weak layer.  Add into the mix the right terrain (slopes 35 degrees and greater) and a trigger (humans or rapid loading of snow) and the result is avalanches.  

Avalanches could occur within newly formed wind slabs and they could also step down to this weak layer.  Regardless of the actual failure layer, it will be important to avoid slopes 35 degrees and over that have this slab/weak layer combo.


Additional Concern

A continuation of above freezing temperatures in the mid elevations along with occasional rain will make wet loose avalanches another concern today.  Volume of these will be generally low.  Despite this it will be important to recognize and avoid steep terrain that is holding loose, weak and damp snow.  This snowpack issue becomes more concerning when traveling above terrain traps such as cliffs, gullies and trees.


Mountain Weather

The greatest change in the past 24 hours is in the wind category.  Ridgetop winds picked up overnight with the Sunburst weather station averaging in the 20-30 mph range since 10 pm.  Light rain and snow have been falling with the rain/snow line fluctuating between 1,500 - 2,000’.  Temperatures as you might guess have been warm with ridgetops in the low 30s F.

Today expect snow and rain showers throughout the day.  Rain/snow line should hover around the 1,500’ mark.  Snowfall amounts will be in the 2-3” range above this line.  Winds will be out of the East at 15-20 mph with higher gusts.  Temperatures will remain mild with ridgetops in the low 30s F.

The extended outlook shows a continuation of warm temperatures and precipitation.  Sunday night into Monday looks to bring the next round of more significant moisture and warm temperatures to the area.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32 1 .1 36
Summit Lake (1400') 28 0 0 9
Alyeska Mid (1700') 31 Trace .1 26

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 30 E 15 46
Seattle Ridge(2400') 30 NE 8 34

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: Nov 18, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedOnly a few inches of snow sits at the motorized lot, not enough to open for snowmachining at this time. Updated Nov. 18, 2017
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail is expected to 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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