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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Sunday, February 26th 2017
Created: Feb 26th 5:13 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.
1 Low Treeline / 1,000'-2,500' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
 Show the Complete North American Avalanche Danger Scale
Special Announcement

Elevated avalanche danger exists in Hatcher Pass. Click HERE for a several reports about a human triggered slab avalanche near Hatch Peak yesterday. Click HERE for the Hatcher Pass Avalanche Center advisory and more info about the current snowpack.

Friends of the Chugach National Forest Avalanche Center is an official Pick. Click. Give. organization. When you apply for your PFD please considering supporting your public avalanche center!!


The Bottom Line

The avalanche danger is MODERATE above 2,000' in the Alpine where triggering a 2-3' slab avalanche in steep terrain is still possible on all aspects. In addition, there are a handful of other avalanche concerns including shallow wind slabs, cornice falls, sluffs and glide avalanches. 

Below 2,000' there is a LOW danger where triggering an avalanche is unlikely due to a snowpack consisting of hard crusts.

In Summit Lake, Girdwood, and on the southern end of Turnagain near Johnson Pass triggering a deeper more dangerous avalanche near the ground is still possible, but will be hard to trigger.

Check out the Saturday Summit Summary HERE.

 


Primary Concern

Above 2000' a widespread layer of buried surface hoar remains a concern on steep slopes, where triggering an avalanche 2-3’ deep is becoming tougher by the day as the snowpack slowly stabilizes and adjusts. Relatively calm weather this week has allowed for folks to push further into the mountains with no reports of avalanche activity since last Saturday (2/18). However, this weekend it is important remember that poor snowpack structure still exists and triggering a slab avalanche could have high consequences. 

Yesterday stability tests on the West face of Corn Biscuit were a bit alarming with propagation on the buried surface hoar layer as well as near the ground on basal facets. These kinds of stability results are confusing when you see dozens of people ski/ride steeper parts of the adjacent slope without incident. This is an example of the high level of uncertainty with this type of avalanche problem. Tipping the balanche may require a big trigger (snow machine or multiple people on a slope) hitting just the right trigger spot. Thinner areas of the snowpack in steep terrain near rock bands or scoured features are places to avoid. A helpful way to think about this problem is to consider the consequences of a slope if it slides and identify and avoid terrain traps (gullies, cliffs, or trees below). Be aware that obvious clues like “whumpfing” or recent avalanche activity are unlikely. 

Deep Persistent Slab: We continue to find various layers of weak faceted snow and depth hoar near the bottom of the pack in certain areas. This includes Summit Lake zone, and some areas in Girdwood Valley and towards the Southern end of Turnagain near Johnson Pass. Similar to the problem above, these layers will be very tough to trigger, but a possibility remains in places with this structure. 


Secondary Concern

Wind slabs: Loose surface snow and brief periods of moderate winds this week have formed shallow wind slabs in the alpine. Today expect ridge top wind to be in the 10-20mph range from the NW - this wind direction can funnel through some parts of Turnagain Pass from a Southerly direction. There remains plenty of snow available for transport and newly forming shallow wind slabs will be possible a variety of aspects. Watch for pillowed or drifted snow or where the snow may feel stiff and ”upside down.” Identify steep features like convexities or gullies where a shallow wind slab could knock you off our feet. Blowing snow and shooting cracks will be obvious clues to look for if the wind pick up today. 

Loose snow avalanches: The top 6” of surface snow is loose and sluffs may be easy to initiate and fast moving on steep terrain features protected from the winds. 

Cornices: Remember these unpredictable hazards can break farther back onto a ridge than expected and have the potential to trigger an avalanche on the slope below. Give cornices extra space and avoid being under them. 

Glide avalanches: There is a new glide crack above the flats along Seattle Ridge, just looker's left of the up-track and Repeat Offender slide path. Avoid hanging out under this crack and any others you may see - these release without warning and are very destructive.

Sunshine: Today skies may be partly sunny and solar warming may trigger loose snow avalanches in steep Southerly aspects. 

 

Large cornice on SW aspect of Magnum

 

Glide crack on Seattle Ridge has been slowly opening throughout the week

 


Mountain Weather

Yesterday skies were sunning the morning with high clouds moving in late afternoon. Light Northwest ridge top winds (5-15mph) were observed yesterday and temperatures were in the mid to low 20F’s. Some low lying fog was present in parts of Turnagain Arm. Overnight NW winds bumped up into the 10-20mph range. 

Today skies are expected to become partly cloudy by the afternoon and temperatures will remain the 20F’s today. Northwest winds could range from 10-20mph. There is a chance of snow flurries in the morning. 

There is still some possibility for intermittent snow flurries in the next few days, but cooler temperatures are anticipated this week as a high pressure moves into the region. There is also talk of outflow winds by mid week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 26  66 
Summit Lake (1400') 25  31 
Alyeska Mid (1700') 27  61 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  NW  24 
Seattle Ridge(2400') 25   NNW 43 

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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