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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, February 22nd 2019 7:00 am by Heather Thamm
ARCHIVED ADVISORY - All advisories expire after 24 hours from the posting date/time.
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The Bottom Line

The avalanche danger remains CONSIDERABLE in the Alpine due to strong Northwest winds that have loaded leeward terrain. Human triggered wind slabs 1-2' are likely above treeline on slopes steeper than 35 degrees. Natural wind slabs are possible. Additionally, give cornices a wide berth and avoid travel under glide cracks. Blowing snow, shooting cracks and any recent avalanches are signs of unstable snow. 

At treeline and below, MODERATE avalanche danger exists for triggering an isolated wind slab in areas exposed to recent winds.

GIRDWOOD / PORTAGE / PLACER: Wind slabs could be deeper, up to 2' thick, due to more snow that has fallen over the last 6 days and significant wind loading. Mid and lower elevations are also suspect due to 8-12" of snow sitting on a slick bed surface.

SUMMIT LAKE / JOHNSON PASS: This area has a very poor snowpack structure with multiple weak layers. Large natural avalanches were observed in this zone yesterday. Triggering a larger, more dangerous slab, breaking deeper in the snowpack is a concern today. Conservative terrain choices and a cautious mindset is advised.

SEWARD / LOST LAKE: Recent snow has fallen this week and strong Northwest winds were observed in this zone as well. Wind slab avalanches are possible and more uncertainty about a deeper more dangerous avalanche hazard exists due to very little info about the snowpack.


 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.
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.
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

Heading to Hatcher Pass? Large human triggered avalanches have occurred this week and dangerous avalanche conditions are expected to continue. Be sure to read the mid-week snow and avalanche summary, and check out recent observations and follow Hatcher Pass Avalanche Center Facebook page for more updates. 


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday an impressive Northwest outflow wind event impacted our region. Starting around noon numerous large natural avalanches released in Summit Lake on East and Southeast aspects along the road corridor on Fresno Peak, Colorado Peak, and Summit Peak. This includes a close call by a group (myself included) on Fresno Ridge who turned around due building winds and rapid loading. Just after our descent a large natural avalanche ran adjacent to the route we had descended. This avalanche had a powerful powder blast that blew over some of our tracks. See the report HERE for details.

In some parts of our region winds were much stronger and more sustained than forecasted. Mile 43 along the Alaska Railroad reported average speeds in the 40s and gusts in the 60-80s mph. In Summit Lake wind speeds were likely gusting into the 50s mph and higher at times, but was not accurately captured by MP 45 weather station. In Turnagain Pass the winds were milder, Seattle Ridge weather station and Sunburst averaged 15mph with gusts in the 20-30s mph. Blowing snow was observed throughout this area, but not nearly as much as in Summit Lake. Several fresh natural wind slabs were observed on the SE aspect of Seattle Ridge near the motorized lot. By comparison these avalanches were much smaller in size and only ran a few hundred yards.

Today Northwest winds will start to diminish this morning and become light by the afternoon. Natural avalanche activity is becoming less likely as winds decrease, but human triggered avalanches will be a concern on aspects that received significant loading. East and Southeast aspects are the most suspect, but cross loading may exist on all aspects. Be suspect of smooth supportable surfaces or pillowed snow on steep or unsupported terrain. These slab may have formed on weak faceted snow buried last weekend (2/16) and may initiate easily with the weight of a person or snowmachine. Shooting cracks will be an obvious clue wind slabs are touchy. Wind slabs could be small and isolated or large enough to bury a person if one releases in an older mid-pack layer. More on this below.

*Although there is not much loose snow available at this point, solar radiation may warm up Southerly aspects when winds calm down. Roller balls and small wet loose point releases are possible on steep Southerly aspects near rocks. 

This photo above illustrates the difference between the large avalanches that released naturally in Summit Lake yesterday compared to the photo below of the avalanche activity on Seattle Ridge in Turnagain Pass. These two pictures are a good example of how different the snowpack and weather can be from one part of our zone to another.  Also note the ski tracks on looker left. Our group feels lucky we chose to descend when we did.  

These 3 wind slabs were the only recent avalanches observed yesterday in Turnagain Pass where winds were much milder than Summit Lake.

  


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

In the periphery zones of Summit Lake and Johnson Pass an overall poor snowpack structure exists. Yesterday’s natural avalanche cycle in Summit Lake was clear evidence that these older layers are still reactive to additional loading. In Turnagain Pass, where the snowpack is deeper and less loading occurred, the balance was not tipped as of mid-day. However… a layer of widespread buried surface hoar is lurking 1.5’-3’ below the surface across the region. Stability tests over the last 10 days have not been very reactive and the last human triggered avalanche on this layer was over two weeks ago in Turnagain. With that said, some uncertainty exists due to yesterday’s loading event. It is good to keep in mind triggering an avalanche today could be larger than expected on slopes that have recently been loaded. Northwest winds this morning may still be actively loading leeward aspects. Triggering a deeper more dangerous avalanche is more likely in and around Summit Lake where the snowpack has proven itself guilty. Conservative decision making and cautious route selection is recommended. Be on the lookout for obvious clues like whumpfing, shooting cracks and recent avalanches.

 

Rapid loading due to strong winds overloaded an old weak snowpack and caused avalanche activity to run farther and faster than expected in Summit Lake yesterday. This powder blast from the second avalanche crossed over the terrain we descended. For the full report click HERE. 


Additional Concern

Glide Avalanches

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. New glide cracks are opening up around our region and the most recent glide crack to avalanche was a few days ago on the south side of Goat mountain in Girdwood Valley on Tuesday. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.


Mountain Weather

Yesterday: Skies were overcast becoming mostly sunny by the late afternoon. Moderate to strong Northwest winds were observed across the region. Most of the local ridgetop weather stations recorded average speeds around 15mph with gusts in the 30s mph, but in some areas winds were more sustained and much stronger. Temperatures average in the 20s F. At sea level temps reached a high of 30 F and upper elevations temps dipped to low-teens F overnight.

Today: Clear skies and sun will dominate as high pressure settles in over most of Southcentral, Alaska today. Gusty Northwest winds will quiet down by early this afternoon to 5-15mph. Temperatures will be in the teens F at ridgetops and low-mid 20s F at lower elevations. Valley fog is likely. Expect inverted temperatures wherever fog develops.

Tomorrow: Sunny clear skies will persist through the weekend and into next week. Expect inverted temperatures with ridgetops averaging in the 20s F. Valley bottoms will be in the low teens F to single digits F. Daily temperatures swings with solar warming and warmer air aloft may allow ridge tops to reach warmer than normal temperatures for this time of year. Valley fog is possible and will keep temps in the teens F in the lower elevations. Winds will be light to calm.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 25  62
Summit Lake (1400') 25  31 
Alyeska Mid (1700') 23  .01  57 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 13  NW  11   39
Seattle Ridge(2400') 21  NW  11  33 

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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