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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Kevin Wright  
Saturday, December 15th 2012
Created: Dec 15th 6:35 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.
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.
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
The Hoarding Marmot
The Bottom Line

ANNOUNCEMENT

Turnagain Pass, Johnson Pass and riding areas in the Seward District of Chugach National Forest will be OPEN to motorized use today.  Placer river, Skookum valley, and 20 mile remain CLOSED due to shallow snow cover. 

BOTTOM LINE

Most areas in the backcountry are showing a MODERATE danger rating, with wind loaded slopes above treeline on the dangerous end of the MODERATE spectrum.  Small avalanches will be possible in specific areas, large avalanches may be triggered in large terrain.

Natural avalanche activity as recently as 2 days ago combined with a low amount of backcountry skiing activity (slope testing) is giving us significant uncertainty in evaluating the danger rating.  What we do know - recent natural avalanches caused by wind, very poor snow structure with multiple weak layers, 2 snowfall events in the last week, a concensus in the avalanche community that our current snowpack is bad news.  Some areas are more likely to find avalanches including east facing slopes and north and south crossloaded gullys and anywhere with recent windslab on top of the facets and buried surface hoar. 


Primary Concern

Recent wind slab from Thursday is the primary concern.  The worst areas will have a stiff layer of surface snow on top of very weak facets.  This means above treeline in wind loaded zones including east facing slopes or pockets of wind slab in specific cross loaded terrain.  The most obvious examples we have of this are the aspects easily visible from the highway of Seattle ridge in Turnagain Pass and Fresno ridge near Summit Lake.  Both of these areas had large natural avalanches caused by wind loading.  As time goes on, the likelihood of triggering similar slopes is diminishing, but the rate of stabilizing is slow due to the persistent nature of our weak layers. 

There is no doubt in my mind that avalanches can be triggered today in the right terrain.  Watch out for slopes steeper than 35 degrees and signs of recent wind loading.  Avalanche size and destructive potential will be directly correlated to the size and consequences of the terrain. 


Secondary Concern

The only change in the persistant weak layers in the last week is they are now buried by 1-2 feet of new snow.  Which means that we now have heavier snow sitting on the extremely weak snow from the early season.  When you add the wind loading component to the mix, it becomes a dangerous recipe.  Yesterday we found frequent whumphing (collapsing) of the weak layers, telling us that they are tenuously carrying the stress of recent snowfall.  That collapse would be the initiation of an avalanche if the slope was steep enough...

It's good to remember that we don't often deal with weak layers on the scale we currently see them.  Our typical strong maritime snowpack has been replaced by a weak and shallow continental snowpack you would more often find in Colorado.  This means that problems don't diminish for days or weeks following a storm.  The only way to ensure safe mountain travel when you find abnormally dangerous conditions is to stay in mellower terrain.  We can't go the same places we could in our normal stable snowpack and expect a positive outcome.

Check out this video from our colleagues in Utah for some good theory on terrain management.


Mountain Weather

Mostly sunny this weekend with colder temperatures.  We may see some stiff northwest wind in the mountains today.  The next chance of snowfall is still a few days away. 

The temperature inversion that gave us comfortable temperatures above treeline yesterday seems to be breaking down this morning.  The coldest areas are showing lower single digit temperatures. 


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). 

Wendy will issue the next advisory Sunday morning, December 16th.

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: Mar 28, 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: OpenPlacer remains open but SKOOKUM DRAINAGE will close to motorized use on April 1st.
Skookum Drainage: OpenSKOOKUM DRAINAGE CLOSES TO MOTORIZED USE ON APRIL 1 annually as per the Chugach National Forest Plan document.
Turnagain Pass: Open
Twentymile: Open
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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