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Avalanche Advisory

Turnagain Area Avalanche Advisory
Monday, February 18th 2019 4:21 am by Aleph Johnston-Bloom
Previous Forecast
BROUGHT TO YOU BY
The Bottom Line

The avalanche danger is CONSIDERABLE due to recent snowfall and wind loading. Human triggered slab avalanches 1-2' thick are likely on slopes 35 degrees and steeper, especially in wind loaded terrain. Additionally, give cornices a wide berth and avoid travel under glide cracks. Careful snowpack evaluation and conservative decision-making are essential if headed into avalanche terrain. Look for signs of instability. 

SUMMIT LAKE / JOHNSON PASS:  This area has a very poor snowpack structure with multiple weak layers. Watch for whumpfing, shooting cracks and recent avalanches. Triggering an avalanche in the new snow has the potential to initiate a more dangerous slab, breaking deeper in the snowpack

SEWARD/ LOST LAKE:  Avalanche danger has risen in this region as well and storm snow avalanches are likely today. 

BYRON GLACIER TRAIL Hikers:  Remember this trail is in avalanche terrain and the popular snow cave is very dangerous and unstable. 


 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

Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Triggering a 1-2' thick slab avalanche on slopes 35 degrees and steeper is likely today. Wind loaded slopes are the most suspect. Yesterday the advisory area saw steady snowfall with an additional 4-10" of snow (favoring Girdwood) and easterly wind loading throughout the day. Sunburst saw gusts into the 80s and Max's into the 60s. Observers noted cracking and small test slopes being easily triggered later in the day. Visibility made Alpine observations difficult. The strong winds eased off in the evening and there was a break in the snowfall. Snow started again early this morning and is forecast to continue today throughout the advisory area. The old wind harden snow surface from before the storm and Saturday's low-density snow will make it tough for the new snow to stick right away. 'Upside-down' snow was noted by observers yesterday. Today look for recent avalanches, shooting cracks and listen for whumpfs or hollow sounding snow. Choose terrain carefully. Cornices may be quite tender and should avoided. 

Storm slab triggered on Sunburst at 1300',  2-17-19. Photo: Elliot Gaddy

Storm slabs triggered on Tincan later in the day, 2-17-19. Photo: Ray Koleser. 

 

 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

New snow and wind loading have the potential to add stress to underlying weak layers. As we have been hammering home for weeks, in Turnagain Pass roughly 1-3' below the snow surface sits a layer of buried surface hoar.  Periphery zones such as Summit Lake and Johnson Pass harbor a poor overall snowpack structure with a variety of weak layers. Although these persistent weak layers have not been reactive lately, additional load may start to tip the balance. It is good to keep in mind that triggering an avalanche today could to step down into old weak layers and initiate a larger more dangerous slide. This is more likely in Summit Lake and the central Kenai mountains. 


Additional Concern

Glide Avalanches

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.


Mountain Weather

Yesterday: Skies were obscured with snow falling throughout the day. Winds were easterly 20-40 mph gusting as high as 88 mph on Sunburst. Temperatures were in the 20Fs to mid 30Fs. Overnight skies were mostly cloudy and winds were easterly 5-15 mph gusting into the 20s.  

Today: Mostly cloudy skies and snow showers, 3-8" of snow forecast. Rain/snow line around 700'. Temperatures in the 20Fs to mid 30Fs. Winds will be southeasterly 5-15 mph with gusts into the 20s. Light snow showers continue overnight with temperatures cooling into the low 20Fs. 

Tomorrow: Skies clearing in the early morning becoming mostly sunny. Winds shifting to the northwest and increasing to 20-30 mph with gusts into the 40s. Temperatures will be in the low to mid 20Fs. The next storm system is forecast to move into the area Wednesday afternoon. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  29  2 0.3  62 
Summit Lake (1400')  30   2   0.2   28 
Alyeska Mid (1700')  29   5  0.6   58  

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 20   NE 20  88 
Seattle Ridge(2400') 25   E  13    38  

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: Jan 28, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
Placer River: Open
Skookum Drainage: Open
Turnagain Pass: Open
Twentymile: Closed
Seward District
Carter Lake: Open
Lost Lake Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Primrose Trail: OpenPlease stay on trail to avoid resource damage through forested areas.
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
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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