Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, February 13th, 2021 - 7:00AM
Expires
Sun, February 14th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations for triggering a wind slab avalanche 1-2′ deep. Any slope with prior wind loading, or wind loaded areas, will be possible for a person to trigger a wind slab. Slabs may be stiff enough to allow a person onto them before releasing and they could be triggered remotely, meaning from the top or the side. Additionally, cornices have grown and give these a wide berth as they could break further back than expected.

SUMMIT LAKE/SNUG/LOST LAKE:  Strong winds on Thursday impacted these zones as well. Human triggered wind slabs are possible and extra caution is recommended.

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Sat, February 13th, 2021
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

The mostly clear skies yesterday gave us a look around at the widespread natural wind slab activity from Thursday’s wind event. Also, a few groups out found wind slabs to be very touchy a day after the wind loading:

Notch Mountain in Girdwood Valley:  A group of skiers triggered two wind slabs, one of which was 12″ deep and had very wide propagation. No one caught. Report from group HERE.

Fresno in Summit Lake: A group of skiers triggered a wind slab up to 16″ deep on a wind loaded slope in Summit Lake. No one caught. Report from group HERE.

 

Notch: Wind slab with wide propagation triggered with a ski cut. 2.12.21. Andy Dennis.

 

Fresno: Wind slab triggered by a ski cut on a wind loaded slope. 2.12.21. Anonymous.

 

Natural wind slab that ran on various layers of weak snow. 2.12.21.

 


Natural wind slab in the Fresno area of Summit Lake. 2.12.21. Anonymous.

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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

It appears a sunny Saturday is on tap for those headed to Turnagain Pass and surrounding areas. It may be in the single digits in the parking lots, but a short climb out of valley bottoms should get us to 20F. The east wind event on Thursday really wreaked some havoc in many areas. There are places where much of the snow simply blew back into the atmosphere, left us anti-tracks, and is gone for good. Yet, it sounds like this isn’t the case everywhere, luckily. If you are in search of those soft snow zones be sure to keep your eyes peeled for prior signs of wind loading and wind slab avalanches.

Wind slabs are the primary concern and could be a bit tricky. These formed over the past couple days and are likely to be sitting on either faceted snow or buried surface hoar. Both of which is keeping them from bonding quickly and why folks were able to get them to release easily yesterday. They should be getting more stubborn as time goes on, but that can add to the tricky-ness. Because of this and their stiffness, they might allow a person onto them before releasing, giving that person less of a chance of escaping. Winds blew at all elevations and slabs could be lurking lower on slopes. Really paying attention to cracking in the snow and hollow feeling snow is key.

Making things a bit more complicated is an older layer of buried surface hoar that may or may not be sitting under an obvious wind slab. In this case softer slabs could be triggered on slopes without an obvious ‘wind slab’ character. Where winds have done minimal damage, this layer is roughly 8-16″ below the surface pending on the area (deeper in Placer Valley, shallower at Turnagain Pass). It is what we call a persistent slab avalanche problem and though it’s showing signs of healing, it’s good to keep on the radar, especially for those less traveled zones.

Good things to keep in mind for today:

  • RED FLAGS to assess wind slabs
    • Cracks that shoot out from you?
    • Whumpfing (collapsing) in the snowpack?
    • Stiff snow over soft snow, hollow feeling snow?
  • Watching for signs of previous wind loading on the surface
  • Safe travel protocol
    • Exposing one person at a time
    • Watching our partners closely
    • What are other groups up to?
    • Having an escape route planned

Cornices: These features grew on Thursday and if ridge-walking today, give them an extra wide berth. Also, limit time under them. A cornice fall may trigger an avalanche below, making a bad situation worse.

 

A skier triggers a very small avalanche on a test slope on Center Ridge yesterday. Small test slopes can be good tools for assessing these wind slabs or persistent slabs. 2.12.21. Joe Stock.

 

Video from Friday 2.12.21 of a natural wind slab on the west face of Seattle Ridge, link HERE

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

Glide cracks continue to open up throughout the area. These cracks could release at any time and be very destructive. Avoid spending time below glide cracks. If you see any new glide activity, please let us know here.

Weather
Sat, February 13th, 2021
Yesterday: Mostly sunny skies with a few high clouds were over the region. Ridgetop winds averaged in the 5-15mph range with gusts into the 30's mph. Temperatures were mild, in the 20'sF above 1,000' and in the teens on the highest peaks. Today: Clear skies are on tap for today, even the satellite doesn't snow any hint of clouds streaming above. However, there could be some valley fog in spots near the Arm. Ridgetop east winds are forecast to remain light to moderate, averaging 5-15mph with periods of 20mph later this afternoon. Temperatures are chilly in valley bottoms (-10 to 10F) as an inversion is in place, while mid and upper elevations are in the teens to 20F. Tomorrow: Clouds are expected to begin moving in tomorrow associated with the next approaching weather front. Only flurries are expected at most. Ridgetop winds bump up again to the 20-30mph range from the east and temperatures should bump back up as well into the teens and 20'sF. It isn't till the middle of this coming week that the models show a precipitation event with a decent re-fresh of snow. PRECIPITATION 24-hour data (6am - 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 23 0 0 118
Summit Lake (1400') 14 0 0 43
Alyeska Mid (1700') 21 0 0 110
RIDGETOP 24-hour data (6am - 6am)
Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 19 NE 11 38
Seattle Ridge (2400') 22 SE 6 15
Observations
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Riding Areas
Updated Tue, June 01st, 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
Closed
Placer River
Closed
It is packrafting and jetboat season!
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
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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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.