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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Graham Predeger  
Tuesday, January 5th 2016
Created: Jan 5th 6:12 am
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.
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
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The Bottom Line

There is a CONSIDERABLE avalanche danger above treeline in the eastern Turnagain Arm region today in the wake of yet another powerful burst of easterly winds and subtropical moisture from yesterday.  Cautious route-finding and conservative decision-making will be essential as a variety of human-triggered storm snow avalanche issues may be found today.

Below treeline the danger is MODERATE due mainly to the threat from avalanches initiating above and running into this lower elevation band.  

Today will mark the tail end of the most recent warm, wet storm that gave us another 1” of water weight and storm force winds at ridgetop locations.  The conservative move today will be to keep your slope angles mellow and give any steep terrain (greater than 30 degrees) another day or two to adjust to this latest shock.  This includes avoiding terrain running under slide paths such as Johnson Pass Trail and Lynx Creek drainage.


Primary Concern

Though we lack information from the upper elevation start zones over the past week due to a very active and stormy weather pattern inhibiting travel, we can anticipate that today will be another day of storm-snow avalanche issues including the potential for winds slabs, storm slabs, and cornice fall.  These are all direct-action avalanche problems that occur during or immediately after a storm and can be exacerbated by a skier or snowmachiner in steep terrain today. 

Wind slabs:  With sustained winds averaging in the mid-50’s mph yesterday (and gusts to 101mph on Sunburst) wind slabs are expected to be 2-5’ deep on leeward slopes, particularly above treeline; though it is worth recognizing that strong winds such as this has a tendency to load slopes far below ridge lines, creating a mid-slope avalanche problem.

Cornices: These most recent storms have provided all the right ingredients to build monumental cornices.  Sustained winds, relatively warm temps and moist snow all act to grow cornices quickly.  The quicker these backcountry bombs add mass, the more unstable they become.  It’ll be wise to steer clear of cornices, as these are likely to trigger a sizeable slab avalanche if falling onto a slope greater than 30 degrees today.

The stronger the prevailing winds, the lower down on the slope a wind slab will form.  Graphic from rockandice.com

Storm slab:  With another 1”of water at Center ridge and 8-12” of snow since Sunday night you can expect storm slabs to be 1-2’ deep and very heavy (saturated) in areas such as the Tincan trees.  Micro-terrain and tree wells can act as unavoidable and dangerous terrain traps if caught up in a heavy, wet storm slab.  The storm snow is settling out rather quickly in the mid-elevations but keep in mind we are still on the tail end of an active loading event today.

NOTE:  In areas such as Summit Lake, the snowpack is shallower and harbors more weak layers under the recent storm snow.  See Wendy’s observation and write-up from a snowboarder-triggered avalanche (Saturday) that failed on a buried surface hoar layer that ran on a mellow (30 degree) slope.


Secondary Concern

Sitting under 5-7' of settled storm snow is a layer of old faceted snow on top of the Thanksgiving Rain Crust. As we pile more and more of a load on top of this facet/crust combo, we come closer to finding the breaking point where stress overcomes strength of the weak layer.  Some of the avalanche activity we’ve seen during this past week may have 'stepped-down' into this deeper layer resulting in very large avalanches.  The deep slab problem provides one more reason to keep terrain choices conservative until we see cooler temperatures and more stable weather allowing our snowpack time to adjust.  This includes limiting your exposure time spent underneath large paths such as those that effect areas such as Johnson pass and the Lynx creek drainage.


Mountain Weather

Yesterday saw this most recent storm front move through the eastern Turnagain arm region with consistent rain falling throughout the day and overnight below about 1300’.  This accounted for another 1” of water weight (10-12” snow above 1,500’) and another day of 100+ mph gusts on Sunburst ridge (@ 3800’).  Ridgetop winds averaged in the mid-50’s from the East with temperatures in the mid 20’s F on ridgetops and low to mid- 30’s at 1,000’.

We can expect continued active weather throughout most of the day today as the tail end of yesterday’s storm moves through.  The rain/ snow line will again be hovering around the 1,200’ level with up to another 6” of snow falling in the mid and upper elevations.  Temps will be in the mid- 30’s at 1,000’.  Predominant winds today will be out of the east in the 25-55mph range at ridgetops and tapering off throughout the day.

Overnight and tomorrow looks to be a brief break in the storm systems before we see yet another warm, wet and windy disturbance roll through the advisory area ahead of the weekend.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 32   6-9  .9  91
Summit Lake (1400') 35  .43 27 
Alyeska Mid (1700') 32   2-4 1.09  63 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 25   NE 54   101
Seattle Ridge(2400') 26  N/A  N/A   N/A

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
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