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Avalanche Advisory

Turnagain Area Avalanche Advisory
Thursday, December 13th 2018 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 in the Alpine and at Treeline where triggering a slab 1-3’ deep is possible. Triggering a windslab or getting caught up in a loose snow avalanche will be possible in steep terrain. Keep an eye out for glide cracks and avoid traveling underneath this unpredictable avalanche hazard.

Assess the snowpack as you travel, identify areas of concern and evaluate consequences.

GIRDWOOD: Windslab 1-2’ thick are possible on leeward features in the alpine due to higher snow totals and elevated ridgetops winds yesterday.


 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

If you are heading to Hatcher Pass make sure to read a recent report from Hatch Peak on Sunday where a skier was fully buried and recovered without injury.  Be aware alaskasnow.org is undergoing a system-wide website update and Hatcher Pass Avalanche Center webpage may look very different when it is finished. For now stay current by following the new Hatcher Pass Avalanche Center mid-week update HERE. 

Looking for avalanche courses or evening presentations? Check out our calendar page! There are two CNFAIC evening discussions coming up - these are FREE and a great way to get your head back in the avalanche game. TONIGHT 7pm-8:30pm - 'Tales from the Pit' at Blue & Gold Boardshop in Anchorage!


Avalanche Problem 1

Wind Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

Yesterday morning an unexpected sleeper storm was centered over Girdwood and dumped 6-12” of very low-density snow. Snow totals were greater in the alpine. Turnagain Pass received 3” along the road and up to 10” at higher elevations. Winds in the afternoon along ridgetops picked up for a few hours 10-15mph with some gusts in the 20s-40s mph. Triggering an isolated windslab on leeward and cross-loaded features will be possible. Look for smooth or pillow shaped features. Evaluate the snow and terrain as you travel and keep in mind the consequences should even a small rug get pulled out from underneath you.

In areas where winds didn’t change the surface expect new snow to be loose and unconsolidated. Don’t be surprised by 'sluffing' and loose snow moving faster than expected.

Low density loose snow was sluffing easily on steeper features yesterday at Tincan. Photo credit: Tully LaBelle-Hamer


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

There remains some uncertainty around weak snow within older layers of the snowpack. Observations this week have found a facet/crust combo 1-2’ below the surface in the mid-elevations (2000’ – 2700’.) Large collapses “whumpfs” were experienced on Magnum’s NW shoulder on Tuesday and stability tests were quite reactive in this zone. It’s unknown how intact this structure exists into the Alpine. On the Northern end of Turnagain Pass stability tests have been showing a strengthening snowpack at higher elevations. However keep in mind that we’ve seen a lot of snow over the last week and we don’t have a lot of snowpack info. It’s still early season. Areas with a thinner snowpack are more suspect for weaker and unstable snow including the Southern-end of Turnagain Pass, Summit Lake and Girdwood Valley. In general North and East aspects have a tendency to be thinner and there is a zone in the mid-elevations where the snowpack quickly transitions to shallower depths. 

Be on the lookout for red flag warnings like whumpfing’, shooting cracks, new avalanche activity or any changes in weather. Keep in mind there is a lot of snow available for transport. Any sign of increased winds could form reactive wind slabs or add stress to a persistent slab.

This is a good example of where the snow quickly transitions shallow and weaker snowpack in the mid elevations. This structure may be more widespread on the Southern end of Turnagain Pass and in Summit Lake. 


Additional Concern

Glide Avalanches

The first glide cracks of the season were seen on Sunburst SW face under the weather station. A glide crack is the snowpack being pulled by gravity downhill along the ground. They can release at any moment without warning and are usually not associated with human triggers. The best way to manage this hazard is to avoid being on or beneath any slopes with cracks opening up. 

Photo taken on Tues December 11, 2018 of new glide cracks on SW face of Sunburst


Mountain Weather

Yesterday: Snow flurries were the most intense in the morning between 6am to 10am. Turnagain received 3” of low-density snow along the road and Girdwood 6-10” at valley bottom. Winds were light with the exception of a few hours along ridgetops where winds increased to 10-15mph with gusts in the 20-40s. Temps at sea level were in the low 20Fs and ridgetops dropped into the single digits.

Today: Temps will be similar with single digits at ridgetops and low-20Fs near sea level. Snow flurries will diminish becoming mostly sunny in the afternoon. Winds are expected to be light (5-10mph) from the West and shift to the East by this evening. Tonight snow flurries will return with a few inches possible overnight.

Tomorrow: An active winter weather pattern will persist tomorrow and into the weekend. A continuation of more snow showers, cool temps and light to moderate winds is expected.

*Seattle Ridge weather station anemometer is rimed and not recording wind data.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 18  0.1 33 
Summit Lake (1400') 15  0.3  10 
Alyeska Mid (1700') 17  0.11  20 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') ENE  30 
Seattle Ridge(2400') 14  *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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