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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Sunday, December 21st 2014
Created: Dec 21st 6:22 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 Hoarding Marmot
The Bottom Line

The avalanche danger in the alpine (2,500-5,000’) is CONSIDERABLE.  The chances of triggering an avalanche above 2,500’ are trending towards the low end of the scale but the consequences of being caught remain high.  Slabs up to 3’ in depth could be triggered in steep terrain and propagate across entire slopes today.

The avalanche danger is MODERATE in the upper reaches of the treeline (2,000’-2,500’) elevations.  It will be possible to trigger slabs 1-2' in depth in steep terrain over 40 degrees.  Avalanches triggered in the alpine have the potential to run down into this elevation band today.  Triggering an avalanche in the lower portion (1,000’-2,000’) of this elevation band is unlikely today and the avalanche danger is LOW.

Below 1,000’ there is not enough snow cover to issue a danger rating.


Primary Concern

It has now been 5 days since the last storm abated.  Slabs up to 3’ deep were dumped on top of a widespread layer of buried surface hoar.  This layer has remained intact and is very slowly adjusting to this most recent load.  This combination of slab over weak layer is keeping the danger elevated mainly because the consequences remain high if one were to trigger an avalanche today.

On the plus side, the likelihood of triggering an avalanche has been on the decline since this last loading event.  As it becomes more difficult to trigger avalanches, it is important to pay attention to and avoid areas where that likelihood is higher.  These areas are what we commonly refer to as trigger points. 

Here are some examples of trigger points:

Steep rollovers and convex slopes.  These features have gravity working against the snowpack making it easier for slabs to release.

Thin spots, where the snow is shallow and weak.  In these areas it is easier to impact the weak layer because it is closer to the surface.  Exposed rocks and partially wind scoured slopes are where you will typically find these spots.

These are the main areas to avoid today, especially when they connect directly to steeper and bigger terrain.  Choosing to recreate on large, open slopes with a variety of slope angles and potential trigger points is a roll of the dice today.  You might get away with not triggering a slide or you might not.  The best tactic is to hedge your bets by sticking to lower angle non committing terrain and give this slab/weak layer combo more time to heal.

A quick video describing these concepts:

 


Mountain Weather

Yesterday was another day of relatively calm weather.  Temperatures were in the 20s F at ridge top level, winds were calm and no new precipitation fell during the day.

Light snowfall has begun this morning with stations reporting 1-2” of new snow.  Expect to see continued light snowfall as a weak low pressure center spins around the Kenai peninsula today.  Accumulation of an additional 1-3" of snow is possible by the end of the day.  Winds will be light out of the East at 5 mph.  Temperatures at 1,000’ will be right around 32 degrees F.

The extended outlook is calling for a continuation of light snow showers into the early part of the week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 29  1 .1 27
Summit Lake (1400') 25  trace .1  4
Alyeska Mid (1700') 28  2.5 .2 17.3

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812')  27 E 10  18
Seattle Ridge(2400')  25  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: Apr 11, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease park on road in and leave the turnaround (near outhouse) open for trailers to turn around.
Placer River: OpenWide swaths of open river in the Placer Valley. Travel with extreme caution!
Skookum Drainage: ClosedSKOOKUM DRAINAGE CLOSED TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: ClosedClosed for the remainder of the 2017 season.
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Primrose Trail: OpenPlease STAY ON existing and hardened trail surface through the lower sections of this route.
Resurrection Pass Trail: ClosedClosed for 2016/17 winter season. This is a non-motorized season. This alternates every other year and will open again during the 2017/18 winter.
Snug Harbor: Open
South Fork Snow River Corridor: Open
Summit Lake: Open

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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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