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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, February 14th 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 MODERATE above 2000'. Triggering a small wind slab will be possible on steep, leeward terrain features. There is also a chance of triggering a larger slab avalanche 1-3’ thick on slopes 35 degrees and steeper. Give cornices a wide berth, avoid travel under glide cracks. Several glide cracks have released over the last few days.

SUMMIT LAKE / JOHNSON PASS: Areas south of Turnagain Pass harbor a thinner, weaker snowpack with multiple weak layers present including the MLK buried surface hoar. Strong winds yesterday have added stress to the snowpack across the region. In addition to wind slabs keep in mind this zone may have more potential for triggering a larger avalanche. Choose terrain wisely and 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.
Special Announcement

Heading to Hatcher Pass? Be sure to check out the Hatcher Pass Avalanche Center mid-week snow and avalanche summary and observations page for current conditions.


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

A strong outflow wind event triggered a handful of natural wind slab avalanches across our region yesterday. Most of these occurred in Summit Lake, but one was seen near Bertha Creek on Seattle Ridge and one on Max’s Mountain in Girdwood. Northwest winds averaging 20-40mph were seen drifting snow along many ridge tops. This wind direction creates unusual wind loading patterns opposite our normal Easterly storm track direction. Aspects that are shallow and wind scoured will be more loaded than usual. Another challenge is Sunburst weather station is sheltered from this wind direction and not necessarily representative of the full extent of this wind event. For comparison a weather station along the Alaska railroad corridor, South of Grandview, recorded NW winds 30-40mph with gusts in the 60mph’s most of the day. Keep this in mind if you head into the mountains. Hard supportable snow should be suspect and can release once well onto a slope. Wind slabs could be small and shallow or larger if they step down to older weak snow. Northwest winds have backed down overnight, but will remain Moderate, 10-25mph at higher elevations. Any active wind loading or shooting cracks will be obvious clues wind slabs are still tender. 

CORNICES: Cornices are looming large in some of the Alpine terrain. Yesterday’s wind may have added additional stress. Give them an extra wide berth as they often break farther back than expected.

A wind slab released sometime yesterday afternoon on Max's West face in Girdwood Valley. This avalanche was likely human triggered, based on the ski tracks above and below, but those details have not been confirmed. 

 


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday’s wind event added stress to older weaker layers within our existing snowpack. This was the case in Summit Lake where several avalanches released near the ground in shallow snowpack zones on East facing aspects of Summit Peak. In deeper snowpack zones, like Turnagain and Girdwood, a wide spread layer of buried surface hoar sits 1-3’ below the surface. For those just tuning in, the MLK buried surface hoar (buried on Martin Luther King day) was the culprit in numerous human triggered avalanches over the last two and half weeks. The last human triggered avalanche occurred 8 days ago on Eddies, remotely triggered from a ridge onto a steep, unsupported slope. The question remains, can person or snowmachine tip the balance? At this point the jury is out, but due to the nature of buried surface hoar and yesterday’s wind loading event, this layer is still suspect.

Keep the MLK surface hoar in mind and remember:

  1. This weak layer is widespread in the region and seems to be particularly suspect between 2000'-2500' due to a melt-freeze crust associated with it.
  2. Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready.
  3. Wind loaded steep features, large connected and unsupported slopes are the most suspect. As always, one can simply avoid high consequence terrain and stick to slopes under 35 degrees with nothing steeper above to avoid the issue.

 

Strong winds triggered several wind slabs that stepped down to older weaker snow on East facing terrain of Summit Peak in Summit Lake. Summit Lake in general has a shallower and weak snowpack than Turnagain. Areas like Johnson Pass and Lynx Creek may also harbor a similar structure.


Additional Concern

Glide Avalanches

Glide cracks are on the move and becoming more active this week. Yesterday a glide avalanched in Summit Lake and another one release in Girdwood Valley on Monday, on Goat Mountain. There are a handful of new cracks opening up including one spotted yesterday on Seattle Ridge, Repeat Offender, just South of the up-track. Several glide cracks threaten popular skin track routes on the non-motorized side of the road, like the South facing slopes of Lipps and Magnum. Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. We’ve seen glides avalanche when temperatures drop into the single digits, like yesterday, and when temperatures are above freezing. The best way to manage this problem is to identify their location and avoid traveling under their runout. This can be especially frustrating if glide cracks are opening up in popular terrain.

A glide crack opening on Seattle Ridge, on a Southeast aspect of Repeat Offender.


Mountain Weather

Yesterday: Skies were clear and gusty outflow winds dominated our region. Northwest winds in the upper elevations were Moderate to Strong, averaging 15-40mph. Sunburst weather is commonly sheltered from NW winds and recorded moderate winds 10-15mph with gusts to 30mph. As opposed to the MP 43 weather station along the Railroad corridor, South of Grandview, MP 43 recorded steady NW winds 30-40's mph with gusts in the 60’s. Temperatures along ridgetops dropped into the single digits (F) yesterday morning. Temperatures near sea level fell into the teens (F). No precipitation was recorded.

Today: Skies will be clear and sunny. Moderate Northwest outflow winds will continue, but will be more Moderate 10-20mph near ridge tops. Some higher elevation peaks and gap zones like Portage Pass may see NW winds 15-30 mph. Temperatures along ridge tops will remain in the single digits (F) and temps near sea level will remain in the teens (F). No precipitation is expected.

Tomorrow: A continuation of cold temps and clear skies are on tap tomorrow. Outflow winds will diminish by tomorrow morning and shift to more of Easterly direction by mid-day. Temperatures will remain cool, low temps in the single digits and teens.  Friday evening into Saturday morning temperatures will start to increase as a low approaches the Gulf of Alaska. Saturday and into Sunday looks like our next chance for snow showers.

 *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') 16  57 
Summit Lake (1400') 18  24 
Alyeska Mid (1700') 16   0 50 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') WNW  10  30 
Seattle Ridge(2400') 13   *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

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
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