Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, December 5th, 2020 - 7:00AM
Expires
Sun, December 6th, 2020 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE above treeline on all aspects. At elevations above the stout surface crust, watch for stubborn wind slabs and give a cornices a wide berth. Additionally, there is still chance a person could find the wrong spot and trigger a deep slab avalanche in weak snow near the ground.

At elevations at treeline and below the avalanche danger is LOW.

SUMMIT LAKE: With a shallower snowpack in this area, triggering a large slab breaking in faceted snow near the ground is more likely. Observers continue to find concerning stability test results and are experience whumpfing.

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Sat, December 5th, 2020
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Although there were no new avalanches reported yesterday, we did get a photo of what appears to be a cornice fall that triggered a deep slab avalanche in upper Bertha Creek (Gold Pan) area; unknown as to when this occurred (photo below). We also received additional information and high quality photos of the deep slab that was triggered on the west rib of Tincan Proper yesterday (12.3). A big thank you to the skier who skied first and passed along his story of the avalanche HERE.

Cornice triggered deep slab in upper Bertha Creek (Gold Pan). It does have a relatively fresh look, yet it is unknown the time or if it was triggered naturally or by a person on the ridge. Photo from 12.4.20 by Alan Abel.

 

West Rib of Tincan Proper skier triggered avalanche from 12.3.20. Note the rocky bed surface and up to 7′ crown, a clear sign the avalanche broke in the basal facets at the bottom of the snowpack. Photo taken 12.4.20 by Matthew Howard.

 

A wider angle view of the same Tincan avalanche. Photo taken on 12.4.20 by former CNFAIC Director Kevin Wright – thanks Kevin!!

Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

As we can see in the photos above, the weak snow near the ground still has us on guard. Triggering a deep persistent slab, however unlikely, is not out of the question. This issue is at elevations above the dust on crust which is right around 2,500′ and above. Keep in mind, these deep slabs don’t typically give you any signs of instability and all can seem safe and stable before the slope cracks. They often release when someone hits a shallow part in the snowpack, often near rocks, affecting the weak layer. This why they are known for being triggered with the 2nd, 10th or any number of people on the slope.

Shallow snowpack zones:  The south end of Turnagain Pass, Lynx Creek, Silvertip and Summit Lake all sport a shallower snowpack. Triggering a deep slab in these areas is more likely and extra caution is advised.

With a sunny Saturday ahead and easy travel into the Alpine, we can’t forget there are still booby traps lurking. If you are headed to the big game terrain, be sure to keep a close eye on your partners, have an escape route planned and really know your safe zones. Add to that, are there other groups around you on the same terrain to keep an eye on as well?

Otherwise, on the surface, keep an eye out for old stubborn wind slabs. They may still be able to pop out in steep rocky terrain.

Cornices:  These may still be teetering on the brink along ridgelines. Cornice falls are a significant danger in themselves, but could also trigger a large avalanche below. Give them a wide berth.

Weather
Sat, December 5th, 2020

Yesterday:  Scattered high clouds with valley fog was over the region yesterday. Winds were light and variable and temps were chilly, in the teens to single digits.

Today:  Mostly sunny skies with patchy valley fog is expected. Winds should pick up just slightly from the NW and blow in the 5-15mph range. Temperatures have plummeted and sit in the single digits at the parking lots this morning as well as the ridgetops.

Tomorrow:  Clouds should start moving in ahead of the next storm system tomorrow morning. Snow is forecast to fall tomorrow afternoon with a couple inches accumulating by sunset. Temperature will rise with the precipitation and possibly get back into the 30’sF by Monday. Stay tuned.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 9 0 0 56
Summit Lake (1400′) 3 0 0 22
Alyeska Mid (1700′) 11 0 0 56

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 5 var 3 8
Seattle Ridge (2400′) 6 *N/A *N/A *N/A

*Seattle Ridge anemometer is rimed.

Observations
Recent Observations for Turnagain Pass
Date Region Location
04/19/21 Turnagain Avalanche: Triangle, Seattle creek
04/18/21 Turnagain Avalanche: Turnagain Pass Road Obs
04/18/21 Turnagain Observation: Seattle Ridge, approximately 300 yards south of the up track
04/17/21 Turnagain Avalanche: Road obs
04/16/21 Turnagain Avalanche: Seattle Ridge
04/16/21 Turnagain Avalanche: Turnagain Pass, non-motorized side seen from Seattle Ridge
04/16/21 Turnagain Observation: Sunburst
04/15/21 Turnagain Observation: Tincan
04/13/21 Turnagain Observation: Turnagain Pass Road Obs
04/12/21 Turnagain Observation: Tincan
Riding Areas
Updated Tue, April 20th, 2021

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Open
No parking in turnaround at end of the road near the outhouse.
Placer River
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Open
Twentymile
Closed
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Primrose Trail
Open
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Summit Lake
Open

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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.