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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, February 21st 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 is CONSIDERABLE in the Alpine due to strong Northwest winds blowing new snow and loading leeward terrain. Human triggered wind slabs 1-2' are likely above treeline on steep terrain and unsupported slopes. 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 steep terrain.

GIRDWOOD / PORTAGE / PLACER: Slabs could be deeper due to more snow that has fallen over the last 5 days.

SUMMIT LAKE / JOHNSON PASS: This area has a very poor snowpack structure with multiple weak layers. Triggering a larger, more dangerous slab, breaking deeper in the snowpack is possible today as well as natural wind slabs.

SEWARD / LOST LAKE: Recent snow has fallen this week and strong Northwest winds today will elevate the avalanche hazard. Wind slab avalanches are possible and more uncertainty exists in this area due to little info about the snowpack. Look for signs of instability.

 


 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 avalaches have occured this week and dangerous avalanche conditions are expected to continue. Be sure to read their 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
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Large
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Size

Today strong outflow winds will be transporting 3-4” of new snow that fell overnight. Expect Northwest winds to increase this morning to 20-30’s mph along ridges. Taller, more exposed ridgetops and channeled terrain may see gusts in the 40’s or 50’s. Blowing snow will be your first clue wind slabs are forming. Wind slabs could be a few inches thick or up to 1-2’ if they break into a older snow buried this past weekend. Two days ago we observed a similar situation where a period of strong NW winds initiated a handful of natural wind slabs and several people triggered wind slabs in steep terrain. 

Keep in mind a Northwest wind direction creates unusual wind loading patterns opposite our normal Easterly storm track direction. Sunburst weather station doesn’t often reflect the full extend of NW winds and sometimes a South or SW wind direction is observed. Smooth, pillowed surfaces on steep leeward terrain will be most suspect. Wind slabs could be small and isolated or large enough to bury a person if one releases in older snow. Although its becoming less likely in Turnagain Pass, the MLK buried surface hoar is widespread and sits 1.5-3’ below the surface. More on this below.

Cornices are large and strong winds today will be adding additional stress. Give them extra space as they can break farther back onto a ridge than expected.

 

NW winds from two days ago (2/19) observered on Taylor Pass. A similar if not stronger wind event is expected today. Blowing snow is an obvious sign of instability. Photo by Ray Koleser 

Wind slab in Placer Valley Tuesday was likely triggered by snowmachiners along the ridge during a period of active windloading. Overnight we've recieved a few more inches of new snow and additional loading is expected today. Photo by Graham Predeger.


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
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Unlikely

Chance

Historic
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Size

Several persistent weak layers exist within the snowpack across our region, including near surface facets buried on Saturday (2/16.) This is the most likely layer to be initiated today under 1-2’ of snow. In the  periphery zones of Summit Lake and Johnson Pass an overall poor snowpack structure with a variety of weak layers are lurking including the MLK (Martin Luther King day) buried surface hoar and facets mid-pack. The MLK layer has been documented throughout the entire advisory region and was responsible for a number of large human triggered avalanches in late-January and early-February. Although these deeper persistent weak layers have not been reactive lately, additional loading from recent snow and strong winds today 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 and around Summit Lake where a thin and weak snowpack is more vulnerable.

 


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. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.


Mountain Weather

Yesterday: Skies were overcast becoming obscured as snow started falling mid-day. 2-4" of new snow fell (0.2 -0.4" SWE) overnight. Easterly winds increased later afternoon to 10-15mph with gusts in the mid-20s mph. Temperatures were in the teens (F) at ridge tops and upper-20s (F) near sea level. All precipitation remained as snow.

Today: Snow will taper off this morning and skies will start to clear by this afternoon. Northwest outflow winds will increase this morning in channeled terrain and along ridgetops. Expect strong winds 25-35mph with gusts in the 40-50’s to last through the day before decreasing this evening to moderate. Temperatures will be in the teens (F) at ridge tops and low-20s (F) at lower elevations.

Tomorrow: Clear skies and sun are on tap for Southcentral this weekend and into next week as high pressure sets up over mainland, Alaska. Outflow winds will dissipate by tomorrow morning. Temperatures could dip into the single digits (F), but are expected to be more in the teens to low 20F’s. Expect inverted temperatures, cooler temperatures associated with valley bottoms and warmer temps in the Alpine. Valley fog is likely.

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 24  .4  62 
Summit Lake (1400') 23  .2  32 
Alyeska Mid (1700') 23  .15  61 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 16  ENE  11  28 
Seattle Ridge(2400') 21  SE  19 

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: May 06, 2019 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: ClosedClosed as of 4.3.19
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: ClosedClosed as of 5/6. Thanks for a great season all, see you next winter!
Twentymile: ClosedClosed as of 3.20.19 due to lack of snow.
Seward District
Carter Lake: Closed
Lost Lake Trail: ClosedClosed as of 3.22.19 due to lack of snow
Primrose Trail: ClosedClosed as of 4.3.19 due to lack of snow
Resurrection Pass Trail: ClosedClosed for the 2018/19 season. Next season will be open to motorized use.
Snug Harbor: ClosedClose as of 5.1.2019
South Fork Snow River Corridor: ClosedClosed as of 3.20.19 due to lack of snow.
Summit Lake: Closed

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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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