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Avalanche Advisory

Turnagain Area Avalanche Advisory
Wednesday, February 6th 2019 7:00 am by Aleph Johnston-Bloom
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger remains a 'scary' MODERATE on slopes above 2,000'. A weak layer of buried surface hoar is lurking 2-3' below the surface and triggering a large and dangerous hard slab avalanche is still possible. In addition look for recently wind-loaded slopes and roller balls on solar aspects. Avoid cornices and glide cracks and watch your sluff in steep terrain.  

SUMMIT LAKE / JOHNSON PASS:  A variety of weak layers exist in the snowpack and human triggered slab avalanches 1-3' thick remain possible. Choose terrain wisely. 

LOST LAKE:  New snow and wind on Sunday in the Lost Lake and Seward area is expected to have increased the avalanche danger. Look for signs of instability. 

 


 Show the Complete North American Avalanche Danger Scale
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.
1 Low Below Treeline / Below 1,000' Travel Advice: Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
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Avalanche Problem 1

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

The lure of sunshine and soft snow today with a lurking buried weak layer (MLK buried surface hoar) is a spooky combination. Before entering avalanche terrain above 2000' remember the size and consequences of the slides that occurred on Friday on Widowmaker and Jr.'s. Snowpack tests on Saturday in this terrain showed that the layer of surface hoar still has the potential to be triggered. There haven't been avalanches triggered in other zones but the buried surface hoar has been found throughout the advisory area in snow pits from Crow Creek to Summit Lake. The MLK buried surface hoar is sandwiched between hard layers of snow and in places associated with a melt-freeze crust. In some spots it seems to becoming less reactive in snowpack tests but the fact that the MLK buried surface hoar is so widespread is concerning. Is there a chance of triggering a large unsurvivable avalanche?  At this point we are still saying YES. This is the type of weak layer that can't be underestimated or forgotten.

What to keep in mind as you travel today: 

   1-  The weak layer is around 2-3 feet under your feet or snowmachine. 
   2-  No obvious signs of instability are likely to be seen before a slope releases and it may be the 1st track on the slope or the 20th...
   3-  If an avalanche is triggered in this deeper weak layer, it can be very large and propagate across the entire slope. 
   4-  There is still a chance of remotely triggering a slab from the ridge, sides or below.
   5-  Use safe travel protocols: One at a time in avalanche terrain, Stop in safe zones, Watch your partners and Avoid terrain traps!
   6-  Assess the consequences if the slope slides. The larger the terrain = the larger the potential avalanche!

Crown profile from one of the Widowmaker avalanches that occurred Friday, 2-1-19.

 

One of the Widowmaker avalanches, 2-1-19. Photo: Jerry Mann

 MLK buried surface hoar in a quick pit on Sunburst at 2800', 2-4-19.


Avalanche Problem 2

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

There is obvious wind effect in the Alpine from the winds on Sunday day and Monday night. Lingering wind slabs are still possible today. Look for wind loading patterns and be suspect of loaded slopes. Watch for cracking in the surface snow and stiffer snow over softer snow. Although wind slabs are likely to be shallow, they could be more dangerous if they were to step-down and trigger a large slab that breaks in the buried surface hoar discussed above. 

Loose snow avalanches (dry and wet):  Watch your sluff in steep terrain on shaded aspects. In steep terrain receiving direct sunshine look for roller balls and small wet loose avalanches. 

Cornices:  We had a report of a large cornice fall in upper Seattle Creek drainage over the weekend. Give cornices an extra wide berth as they often break farther back than expected. 


Additional Concern

Glide Avalanches

Glide cracks are opening again. We know of one glide avalanche that has released recently in the Summit zone just north of Manitoba. Look out for glide cracks and limit exposure under them! 


Mountain Weather

Yesterday: Mostly cloudy with light snow showers in the early morning. Winds were easterly 5-15 mph with gusts into the 20s, decreasing to light winds below 5 mph overnight. Temperatures were in the low 20Fs at upper elevations and hovered near 30F at sea level.

Today: Mostly cloudy skies with a slight chance of flurries in the morning becoming mostly sunny by this afternoon. Calm easterly winds throughout the day with gusts up to 5 mph. Temperatures will be in the 20Fs at upper elevations and in the 30Fs at sea level.

Tomorrow: Mostly cloudy skies in the morning, becoming partly sunny in the afternoon. Light westerly winds with temperatures in the 20Fs to low 30Fs. Friday looks to be similar. There is a chance of snow over the weekend and a more active pattern forecast for next week. Stay tuned! 


*The Seattle Ridge anemometer (wind sensor) was destroyed. We have a replacement on the way and it should be operational by mid February.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880')  28 59 
Summit Lake (1400')  27 27 
Alyeska Mid (1700')  27  0    0   53 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 21   E 21 
Seattle Ridge(2400') 26   *N/A *N/A  *N/A 

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 22, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Open
Placer River: ClosedClosed as of 3.20.19 due to lack of snow.
Skookum Drainage: ClosedPlacer access closed as of 3.20.19 due to lack of snow.
Turnagain Pass: Open
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Open
Lost Lake Trail: ClosedClosed as of 3/22. Unfortunately HEAVY rain over the past week has washed much of the snow off the lower stretches of this trail.
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: ClosedClosed as of 3.20.19 due to lack of snow.
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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