Turnagain Pass RSS

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Sat, December 5th, 2020 - 7:00AM
Sun, December 6th, 2020 - 7:00AM
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.

Special Announcements
Sat, December 5th, 2020
Above 2,500'
2 - Moderate
Avalanche risk
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Dangerous avalanche conditions. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
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
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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.

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.

Recent Observations for Turnagain Pass
Date Region Location
11/16/23 Turnagain Observation: Tincan Common
11/14/23 Turnagain Observation: Sunburst/Magnum
11/14/23 Turnagain Observation: Seattle Ridge
11/13/23 Turnagain Avalanche: Tincan Trees
11/12/23 Turnagain Observation: Sunburst
11/12/23 Turnagain Avalanche: Goldpan – avalanche
11/11/23 Turnagain Observation: Tincan Common
11/11/23 Turnagain Observation: Taylor Pass – Sunburst
11/10/23 Turnagain Observation: Tincan
11/10/23 Turnagain Observation: Tincan Trees
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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.