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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, February 12th 2018 5:37 am by Wendy Wagner
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

There is a CONSIDERABLE avalanche danger above 1,000' due to snowfall overnight and strong winds. Natural avalanches within the new storm snow are possible and human triggered avalanches are likely. Fresh wind slabs up to a foot thick, and possibly 2 feet thick, should be expected on slopes with recent wind loading. Additionally, weak layers deeper in the snowpack may become overloaded and release, creating a much larger avalanche up to 3' thick. Below 1,000' the danger is MODERATE for wet loose sluffs.


 Show the Complete North American Avalanche Danger Scale
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.
Special Announcement

Coming up this Friday night, Feb 16th - The 2018 SNOWBALL!! Join the CNFAIC, our non-Profit Friends group and Alaska Avalanche School for live music by the Hope Social Club, silent auction, raffle, locally brewed beer and good people. This benefit supports avalanche safety in Southcentral Alaska, we look forward to seeing you there!!

Coming up Saturday, Feb 17th, from 11am-1230pm - Free Avalanche Beacon Practice with CNFAIC! We will be hosting a short workshop on how to effectively perform a companion rescuce. Open to all users and all levels; swing by on your way to the hills if your are just getting into avalanche safety or simply need a refresher!


Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Overnight saw a quick shot of snowfall that should give us a much needed refresher. This storm was on the warm side however. Along with new moist snow that fell at the mid and upper elevations, rain has fallen up to 200-500' in places. For storm totals at mid-elevations as of 6am this morning:

Girdwood Valley:  8-10+" snow
Turnagain Pass:  5-7" snow
Summit Lake:  6-8" snow

This is clearly not a large storm for our standards, but what is notable is the variety of weak layers we have within, and on the surface of, our pre-existing snowpack. Although the new snow is moist and 'sticky' it will likely have a hard time bonding right away onto the surface - storm snow avalanche issues are below. What is possibly more concerning is what is lurking around 1-2' deep in our snowpack. This is a layer of buried surface hoar from Jan 21 that remains intact in many areas and could be waiting for a slab to form on top of it to start producing large avalanches. This storm has likely created that slab. Hence, today is a day to be extra cautious and evaluate the snowpack carefully. Avalanches releasing in the Jan 21 buried surface hoar could be up to 3' thick. Also, small avalanches within the storm snow could 'step down' and release a much larger and unmanageable slide. This issue is less of a concern on slopes that were heavily tracked out over the past two weeks, and much more on a concern on slopes seeing moderate to no traffic. 

Photo below is from a small wind slab triggered yesterday releasing on the recently buried surface hoar. This was on the North Chutes of Cornbiscuit. Note the crack in the bed surface at the bottom of the photo. This crack is believed to have stepped down to the Jan 21 buried surface hoar, yet that layer did not slide. With more load overnight, we may see avalanche 'step down' to this older weak layer, creating much larger than anticipated avalanches. (Thanks to Mike Records for the photo).

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Avalanche Problem 2

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Storm snow instabilities associated with the new snow overnight and today will be likely. These come in many forms listed below and due to the lesser snow amounts, are expected to be on the smaller side. The most concerning for us however, are wind slabs as they will likely be larger and a less manageable storm snow problem. Bonding between the new and old snow is not expected to be good as the new snow has fallen on a new crop of surface hoar and near surface facets.

Wind Slabs:  Moderate to strong winds coupled with 6-10" of new moist snow have likely formed soft wind slabs up to a foot thick or even two feet in places. Because these slabs are likely sitting on weak old snow, they are expected to be quite sensitive and easy to trigger. 

Storm Slabs:  Out of the wind, on slopes that have more than ~5" of new snow, expect to see soft storm slab avalanches composed of the new snow.

Loose snow sluffs:  Sluffs on steep slopes are likely with the recent new snow.

Wet sluffs:  Below 1,000' where rain is falling on snow, small wet sluffs are likely in the steep terrain.

Roof-a-lanches:  Watch for your roofs to avalanche with the warm temperatures and rain.


Additional Concern

Deep Persistent Slabs

Today's snowfall is only a small load on top of our generally weak snowpack structure in the Alpine (above 3,000'). However, even a small load and warming temperatures could help tip the balance for someone to trigger a large deep slab that breaks in the bottom half of the snowpack. It's good to remember that multiple layers of old buried surface hoar, facets and crusts exist deep in the pack and near the ground. These are not likely to 'wake up', but it's worth keeping in mind, as outliers can happen as with last week's Twin Peaks slide.


Mountain Weather

Overcast skies were over the area yesterday along with snowfall that began late in the day, peaked overnight and is decreasing this morning. Roughly 5-10" of new moist snow has been recorded at mid-elevations with .5-1" of water equivalent. The rain/snow line looks to have been 200-500'. Ridgetop winds were Easterly in the 15-30mph range with gusts to 50mph. Temperatures were mild, in the mid 30's at sea level and the mid 20's along the ridgelines. 

Today, we should see light precipitation possibly add another 1-3" of snow above 500' and light rain below this in some areas. Skies will also start to clear out in certain areas as well. Ridgetop winds are expected to decrease and blow from a Southerly direction in the 5-15mph range before shifting Westerly this evening. Temperatures will remain warm, mid 30'sF at sea level and mid 20'sF along ridgetops before cooling off tonight. 

Tomorrow, Tuesday, we should see mostly clear skies, cooler temperatures and moderate to gusty Westerly winds. Another chance for snow is possible Thursday before, what looks like, mostly clear skies for late in the week.

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  0.4  65 
Summit Lake (1400') 30  0.5  24 
Alyeska Mid (1700') 30  0.8  57 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21  NE  16  44 
Seattle Ridge(2400') 24  SE  24  50 

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: Feb 15, 2018 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: OpenPlease access trail thru open gate and park trucks/ trailers along the road toward the trailhead. Please keep the turnaround (near large signboard) clear for vehicles to TURN AROUND!
Placer River: OpenOpen 2/16. Please avoid private property and AKRR job site at Luebner Lake. Cross railroad tracks if needed, do not ride down tracks, it is illegal.
Skookum Drainage: OpenOpen 2/16. Please avoid private property and AKRR job site at Luebner Lake. Cross railroad tracks if needed, do not ride down tracks, it is illegal.
Turnagain Pass: OpenPlease avoid riding on “Rookie Hill“ and other areas with exposed vegetation. Thank you!
Twentymile: Closed
Seward District
Carter Lake: OpenOpen 2/16.
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: OpenResurrection Pass trail is open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Open
South Fork Snow River Corridor: Closed
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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