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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   John Fitzgerald  
Monday, February 23rd 2015
Created: Feb 23rd 6:51 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.
0 NO RATING Below Treeline / Below 1,000'
 Show the Complete North American Avalanche Danger Scale
Special Announcement

Iron those Carhartts, break out the sequins, and dust off the bolo…its Snowball time! Please join the Friends of the Chugach National Forest Avalanche Information Center and Alaska Avalanche School at Taproot for an “Alaskan Formal” night at 7pm on February 27th.  You won't want to miss this event!


The Bottom Line

The avalanche danger is CONSIDERABLE in the Alpine and Treeline elevations today.  Dense slabs 1-3’ thick have the potential to release naturally on steep sunlit slopes in the Treeline elevations.  Slabs could also be human triggered anywhere from 2,000’ and above.  These slabs have the potential to propagate across large areas and carry, injure or bury a person.


Primary Concern

A widespread layer of weak faceted snow sits anywhere from 1-3’ below the surface from 2,000' and up.  Between 2,000’-3,000’, the aforementioned weak layer has proven to be the most reactive and slowest to “heal” or bond to the overlying slab.  Above 3,000’ that layer still exists and is still reactive

What this all boils down to is this: the likelihood of triggering a dry slab avalanche is highest in the 2,500-3,000’ elevation band.  The likelihood decreases only slightly as you gain elevation, but the consequences remain the same.  Slabs 1-3’ thick have the potential to be triggered by skiers and riders.  These slabs have the potential to propagate across slopes and entrain significant debris along the way.

Staying on terrain 35 degrees or less and avoiding the runout of steeper terrain above you is your best bet for avoiding this avalanche problem today.


Secondary Concern

Sustained warm temps have helped to weaken slabs below the 2,500’ elevation.  Between 2,000-2,500’ sit slabs 1-3’ thick.  Those slabs are sitting on a layer of facets.  Yesterday we received multiple reports of groups experiencing collapsing in this elevation band where the slab has lost strength due to warming.

More recent slabs 6-12” thick that formed 3 days ago are sitting on a sun crust on steep South facing terrain.  Yesterday we observed two natural slab avalanches that released during the day in terrain with this setup (see photo).

Natural avalanche- Seattle Ridge - 2,400' SE Aspect - Crown Depth estimate 1'.  photo: Fitzgerald

Seattle ridge natural Feb 22, 2015

These smaller slabs have the potential to step down to the deeper buried layer of facets.  

This combination of warm temps with slabs over a persistent weak layer is a perfect recipe for wet slab avalanches.  While the air temps are warm, it will be doubly important to pay attention to and avoid sunlit slopes with clearing skies later in the day.


Mountain Weather

A minor meltdown took place over the past 24 hours, with temperatures climbing into the high 30s to low 40s below 2,000’.  Winds were moderate out of the East in the morning and subsided by the afternoon.  Light rain fell up to 2,000’ with Alyeska Mid station picking up the most precip with .2” of rain.

Today expect showery conditions, with the rain/snow line around 2,500’.  Precipitation amounts will be light, in the .1-.2” range.  Winds will be out of the East at 5-10 mph.  Temperatures will climb slightly again, with 40 degrees expected at the 1,000’ level.  Cloud cover will gradually diminish by the evening hours.

The extended outlook is calling for generally drier conditions.  A low pressure system will brush by the area on Wednesday bringing only a slight chance for precip.  Temperatures will cool as we move into the middle part of the week.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 37 rain .1 41
Summit Lake (1400') 37 rain .1 7
Alyeska Mid (1700') 37 rain .2 22

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 29 n/a n/a n/a
Seattle Ridge(2400') 31 n/a 18 44

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 15, 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: Open
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

Subscribe to the Turnagain Area Avalanche Advisory:

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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