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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Friday, February 17th 2017
Created: Feb 17th 5:09 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.
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.
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BP Alaska
Special Announcement

Recent heavy precipitation, strong winds and warm temperatures have created dangerous conditions in the Southern Kenai; this includes the Seward zone (Lost Lake/Carter/etc).  Travel is not recommended in avalanche terrain.  Other regions throughout Southcentral, AK including Chugach State Park and Hatcher Pass have heightened avalanche conditions.

If you haven't seen it yet, click HERE for a near miss report following a large avalanche triggered by a snowmachiner in Lynx Creek in early February. Luckily no one was caught in this avalanche. We want to extend a big thank you to all those involved and willing to share their story. These types of avalanche conditions continue to plague the region.


The Bottom Line

The avalanche danger is CONSIDERABLE on all slopes steeper than 35 degrees above 1,000' in elevation. Slab avalanches anywhere between 1' and 3+' thick are likely to be triggered in the steeper terrain. These could be shallow fresh wind slabs or thicker, and more dangerous, slabs that break in buried weak layers. These larger slabs have the potential to be triggered remotely from the ridge, the side or from below. Cornice falls are also possible today and could trigger a large slab below.

The danger is MODERATE danger below 1,000' where an avalanche triggered above could wash debris into this lower zone.

*Today is a day to keep our terrain choices conservative and stick to mellow slopes away from runout zones from avalanche paths.


Primary Concern

Yesterday was the first day since the beginning of the Valentine's Storm Cycle (beginning Monday, Feb 13th) that no natural avalanches were seen. The storm cycle is fading, but we did get another shot of snow last night, adding another 2-6" to mountains. This last storm cycle has brought a total of 2-3' of dense new snow to the area and simply put, the new snow is not bonding well with the old snow (seen in video). This is due to a weak layer of buried surface hoar along with near surface facets that is sandwiched between the new snow and old harder snow//crusts. Until proven otherwise, this weak interface is suspect to be on all aspects and elevations. 

Things to keep in mind with this 'persistent slab' avalanche problem:

  1. Human triggered slab avalanches (2-3' deep) breaking in this layer are likely in terrain over 35 degrees
  2. Slabs can be triggered remotely, from the ridge, the side or below
  3. In terrain that saw high traffic last weekend, this layer will be more stubborn to trigger, but don't let that lure you into thinking the pack has stabilized
  4. No obvious signs on instability, or red flags, may be present before a slab is triggered
  5. This is the kind of avalanche that could have several tracks on the slope before someone finds the right trigger point (thin ares of the slab). 

What can we do? Terrain management! Sticking to lower angle slopes (under 35 degress with nothing steeper above you) is recommended.

 
Photo below: A look at the bottom of the slab and the weak layer (buried surface hoar) shining in the sun.


Secondary Concern

WIND SLABS:
Strong winds have been impacting the mountains for 6 days now. Although we should see a decrease in ridgeop wind today, the Easterly flow should still be strong enough to load leeward slopes. Wind slabs from the past few days have been around 6" to a foot thick and showing signs of bonding fairly well. However, the problem is this has made for a more solid slab out of the Valentine's Storm snow that sits over the aforementioned buried surface hoar and facets. Nonetheless, fresh winds slabs should still be something to look for and if triggered, could step-down to the weak layer below. Watch for current wind loading and stiffer, hollow feeling snow over softer snow. 

CORNICES:
Cornices have grown substantially during the past week and could release naturally with the ongoing wind/snow. If you find yourself along a ridgeline, give them a wide berth as these could be quite touchy and have a good chance of triggering a slab below. Also, keep in mind if there are other groups underneath you in valley bottoms.

 Wind plume on the NW ridge of Magnum on Turnagain Pass. This was the theme of yesterday's weather.

 

SUN?
If the sun comes out today, watch for quick changes in the snow surface and an increased change for triggering a slab. Moist to wet loose snow avalanches on Southerly aspects should be expected with the first shot of sunshine.


Additional Concern

Weak snow (facets and depth hoar) in the lower layers of the snowpack continues to be a concern in our advisory area. Avalanches occurring in the upper layers of the pack have the potential to step down and release the entire snowpack in some places. If this does happen the volume will be large and could run long distances.  A few of the naturals throughout this last storm looked to have run into older faceted snow. The possibility of these large avalanches is another reason for conservative terrain choices. 

Several natural slab avalanches on a SE aspect of Fishes Breath in Girdwood Valley, including one that stepped down into an older layer of the snowpack. Photo courtesy of Mike Welch


Mountain Weather

Mostly cloudy skies were over the area yesterday with light snow flurries in Girdwood and the North side of Turnagain Pass. During the overnight hours another pulse of moisture moved through adding 4-6" of new snow in the Girdwood Valley, 2-3" in Turnagain Pass and ~7" at Summit Lake. Ridgetop winds continue to be strong during the past 24-hours from an Easterly direction with averages from 25-40mph and gusts to 57mph. Temperatures have been warm, low to mid 30'sF at sea level with a rain/snow mix, at 1,000' in the upper 20'sF and around 20F along the ridgetops. 

For today, continued off-and-on instability showers are expected with similar warm temperatures and a rain/snow mix at sea level. Total snowfall expected is 2-4" (.25 water) today and another 2-5" (.3 water) tonight. There could also be some clearing skies in between these snow showers. Ridgetop winds should decrease slightly from the East and Southeast with averages in the 15-25mph range (still moderate to strong).

Looking ahead to the weekend, clearing skies and cooler temperatures with a few snow flurries are on tap. Stay tuned. 

 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 30  2 0.2  75 
Summit Lake (1400') 30 0.5  35 
Alyeska Mid (1700') 29  4.6  0.37  70 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 18  ENE  29  57 
Seattle Ridge(2400') 23  Rimed  Rimed  Rimed 

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

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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