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Avalanche Advisory

Turnagain Area Avalanche Advisory
Friday, December 21st 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 CONSIDERABLE at all elevations for the mountains surrounding Turnagain Pass. Trigging a storm slab 3-4’ deep is likely in avalanche terrain due to a massive storm that ended yesterday morning. Triggering an unmanageable loose snow avalanche that entrains and picks up momentum is also a real concern. Today’s message is simple, let this storm settle and give the plow drivers time and space to clear parking areas. This also includes Girdwood, Portage, Johnson Pass, and Lynx Creek drainages that received 2-3+’ of snow during this last storm.

SUMMIT LAKE: In Summit Lake a very weak and shallow snowpack exists and human triggered avalanche 2+’ thick are likely in avalanche terrain. 

LOST LAKE: This zone is out of our advisory area, but observations yesterday show the potential for triggering slab avalanches 2-3’ thick on an older weak layer within the snowpack. If headed to this area pay attention for signs of instability like collapsing and recent avalanches.


 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.
3 Considerable Treeline / 1,000'-2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
3 Considerable Below Treeline / Below 1,000' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
Special Announcement

Many riding areas on the Chugach National Forest have opened, but parking is a REAL CONCERN in Turnagain Pass! A Forest order submitted for a Turnagain motorized opening happened to coincide with an unexpected 4ft sleeper storm. The USFS and AK DOT are requesting both motorized and non-motorized users to avoid Turnagain Pass today due to very limited parking. Parking on the road and riding around the motorized lot will prevent plow operators from being able to clear these lots and delay the process through a busy holiday period. This is also serious safety issue. Should you go to Turnagian Pass today, consider heading South of Summit Lake where parking is not an issue.

If you're thinking of heading to Hatcher Pass be aware of dangerous avalanche conditions in this zone. Check out the Hatcher Pass Avalanche Center mid-week summary HERE. 


Avalanche Problem 1

Storm Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
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Large
Small

Size

STORM SLABS: A surprise storm that ended yesterday morning dumped 46” (~4’ and 3.4” SWE) of snow in Turnagain Pass to Johnson Pass. This storm arrived with moderate ridgetop winds and very low-density snow. Natural storm slabs and loose snow avalanches were seen across the forecast zone from Girdwood to Portage.  Triggering a storm slab in terrain 35 degrees and steeper today will be an unmanageable hazard. This new snow has been settling, but moderate ridgetop winds may make this new snow more cohesive and slab-like in the alpine. As always it’s important to give all big storms a few days of rest before easing into steeper terrain. In addition we may see 4-8 inches of additional snow today.

LOOSE SNOW AVALANCHES are a very real concern due 4' of very low-density snow. Triggering a loose snow avalanche could be large and unmanageable. This kind of snow sould easily knock you off your feet and bury you. Avoid all steep terrain features (large and small) over 35 degrees and be extra aware of hidden depressions and creek drainages. Remember that the lower elevations prior to this storm didn't have much snow coverage. 

Climbing over the second berm into the Center Ridge Parking area. Snow totals in the parking lot were measured at 47" at 1:30pm yesterday. 

  

 

Climbing out of Center Ridge Parking lot yesterday. In the background is Seattle Ridge. Many of the gullys on Seattle were full of fresh debris and numerous storm slab crown could be seen with binos.   


Avalanche Problem 2

Persistent Slabs

Almost Certain
Very Likely
Likely
Possible
Unlikely

Chance

Historic
Very Large
Large
Small

Size

We have been monitoring a facet/crust issue mid-pack between 2000-3000’. Prior to this storm this layer was not showing reactivity and so far there has been no known natural activity on this layer in Turnagain Pass. However, with the addition of 4' of new snow, uncertainty remains. This is an additional reason to let the snowpack settle out and to give these layers more time to adjust. 

In the Summit Lake zone there is much more potential for triggering a slab on facets near the ground. Several natural avalanches were seen yesterday on the far Northern end of Summit Pass that may have stepped down into older layers of the snow pack. We have a lot of observations over the last week that demonstrate propagation potential within older weak layers (facet/crust mid-pack and near the ground.) New snow in Summit Lake will be adding stress to these layers and human triggered avalanches are a concern. Look out for whumpfing, cracking, and recent avalanches. Please keep in mind that there is no snowpack info from Johnson Pass and Lynx Creek, which often have a similar snowpack structure as Summit Lake.

SE aspect where storm slabs stepped down to an older deep layer in the zone between Summit and Johnson Pass near the Hope Wye. 

 

If you head to Lost Lake be aware of triggering a slab 2-3' in an older weak layer of the snowpack. This picture was taken yesterday and the timing of this avalanche is unknown and may be a natural avalanche from a different day. Photo and observation courtesy of Iron (iii) Oxide.


Additional Concern

Glide Avalanches

Glide cracks we know about are on Sunburst's SW face under the weather station, SW face of Tincan Proper, Gold Pan area (behind Cornbiscuit/Magnum) and Moose Mt in Summit Lake and crack that did release in the Johnson Pass area. These cracks can release at any moment. They are not associated with human triggers and the best way to manage the hazard is to avoid being on or beneath slopes with cracks. 


Mountain Weather

Yesterday: Skies were broken to overcast. Snow showers were intermitent with a few inches to trace of new snow across the region. Ridgetop winds were light from the East. Temperatures were in the single digits to teens near ridgetops and low 20F’s near sea level.

Today: Expect snow showers throughout the day with 4-8 inches of snow possible. Ridgetop winds are expected to be 10-20 mph with gusts in the mid 20’s mph. Temperatures will increase from the teens to mid 20F’s in the mid and upper elevations. 

Tomorrow: Temperatures may reach low 30F’s tomorrow morning near sea level. More winter weather is expected as another low tracks into our region. Snow showers will continue tomorrow and into Sunday.

*Seattle Ridge weather station is rimed over and not recording any data. 

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 16   0.2 72 
Summit Lake (1400')  0.1 18 
Alyeska Mid (1700') 18  0.1  37 

 

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

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 11  NE  31 
Seattle Ridge(2400') *NA  *NA   *NA   *NA  

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

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
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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