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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Heather Thamm  
Friday, February 13th 2015
Created: Feb 13th 6:01 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.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
Alyeska Pipeline Service Company
The Bottom Line

Today the avalanche danger is mostly MODERATE in the heart of our forecast zone both in the Alpine and at Treeline. Human triggered avalanches 6-10” are possible in steep terrain and could run far on large slope features.

On the Northern end of Turnagain Pass, and in Girdwood and Portage Valley, the danger quickly increases to CONSIDERABLE where thicker slabs exist. In these areas slabs 10-15” are likely to be triggered by a human and could propagate an entire slope.

Today be on the lookout for any obvious signs of instability like recent avalanches, shooting cracks or whoomphing sounds and avoid all large slopes steeper than 35°.


Primary Concern

Several days ago we received a snow event that distributed an uneven amount of snow over Turnagain Pass. On the Southern end of Turnagain slab depths average 6” with pockets as thick as 10” in wind deposited areas. On the Northern side of the pass, average slab depths are 10” with pockets 15+” in places. This new snow was also accompanied by sustained East winds (20-30’s mph) causing the slab to become denser and more cohesive in areas along ridgetops. This uneven slab distribution is sitting on a widespread unstable weak layer of facets.

We are on the scarier side of the MODERATE scale for the heart of our forecast zone. There’s not quite enough new snow in most of Turnagain Pass bump the entire area to CONSIDERABLE, but it could be challenging to know exactly where this line exists. In places where slab depths are shallower like Tincan and Sunburst isolated avalanches up to 10" thick are possible in steep terrain. In places like Eddies and along the Northern end of Seattle Ridge where thicker slabs exist it will be more likely to propagate an entire slope.

In Girdwood the problem is a little harder to evaluate with 6” of new snow covering an older windslab (4-8” thick) which also sits on top of old weak faceted snow.

Yesterday avalanche activity was observed along the Northern side of Seattle Ridge. Forecasters triggered a remote avalanche from 300' away near the Seattle Ridge weather station.  A larger natural avalanche was also observed in this area. There was also a few reports of natural activity near the Girdwood Valley and near Seward.  

 

This avalanche occured on a Southern aspect near Main Bowl on Seattle Ridge and was not witnessed. It is likely to have been triggered naturally yesterday. 

 

 This avalanche was triggered remotely from 300' away on Seattle Ridge near the Seattle Ridge Weather Station. 

Travel Advice

Collapsing sounds will be your first red flag warning sign. If you hear “woomphing” sounds this is a sign that your weight is enough to collapse the weak layer below the slab and reinforces your decision stay off of slopes greater than 35°.

Remote triggered avalanches are a concern for today and it is extra important to be aware of other groups within the same area. If you are traveling along a ridgeline you could remotely trigger an avalanche on an adjacent slope without even realizing it. If you find yourself along a valley floor avoid the run-out zone of large steep slope. Sunburst ridge and Taylor Pass are a good example of places to avoid today.

Careful snowpack evaluation is recomended today. Click HERE for a demonstration on how to perform a hand sheer test to help you understand our current persistent slab problem.

 


Additional Concern

Warmer temps and solar radiation have caused point releases and roller balls on Southern aspects over the last two days. In summit lake yesterday a 6” slab was triggered on Southern aspect during the heat of the day when temperatures were in the mid 30’sF in this area. It is likely that these aspects are developing a crust layer, but if the sun appears today and temperatures creep into the Mid 30's again, be aware of wet (damp) avalanches on South facing slopes.


Mountain Weather

Yesterday temperatures reached into the mid 30’s F below 1500’ with light rain in the morning then clearing off in the afternoon. Only a trace of new snow fell above 1500’. The sun came out in the afternoon keeping temperatures warm, with the hottest part of the day around 2pm. Ridgetop temps climbed into the high 20’sF. After sunset skies remained mostly clear and temperatures dropped into the mid 20’sF. Winds were mostly from the East and averaged 5-15mph along ridgetops.

Overnight temperatures stayed in the mid to high 20’sF and a mostly East wind has been light (5-10mph.) No new precipitation was recorded.

Partly sunny skies are anticipated today with a chance of light precipitation in the evening. Temperatures are expected to be in the low to mid 30’sF at sea level and at higher elevations. Winds from the East may pick up into the 20's along ridgetops.  

Right now it looks like our next best chance for snow accumulation will be on Sunday. 



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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 31  1 0.1 36 
Summit Lake (1400') 28   0  9
Alyeska Mid (1700') 31  0.1  24 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 27  27 
Seattle Ridge(2400') 28  Var.  25 

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
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