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Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sun, February 16th, 2014 - 7:00AM
Expires
Mon, February 17th, 2014 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is MODERATE at all elevations and aspects. Above treeline persistent slab avalanches 2-3′ in depth will be possible to trigger on slopes where weak faceted snow sits above the late January crust. Additionally, triggering a wind slab 1-2′ thick will be possible on lee sides of ridgelines and areas with prior wind loading. Along with the slab avalanche potential just mentioned, sluffing should be expected in the steeper terrain as well as possible cornice falls on ridgelines.

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Sun, February 16th, 2014
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)
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Yesterday’s avalanche activity:
There was one skier/snowboarder triggered wind slab avalanche just off of Tincan’s Hippy Bowl ridgeline (photo below). Additionally, we had reports of three skier triggered persistent slab avalanches in the Eddies area (reported to have failed in weak snow above the January crust). We did not hear from too many folks in other areas despite many parties out enjoying the top-notch powder conditions right now.   **UPDATED at 8:20am – one additional observation was just sent in of a remotely triggered slab in Seattle Creek.

Primary Concern:
Now that the majority of the storm snow from Valentine’s Day has settled out, the top 2-3′ of the snowpack is mostly right-side-up (stronger snow under weaker snow) and composed of all February’s storms. This would be great news if this layer did not rest on weak faceted snow with a uniform crust underneath – giving us a classic “persistent slab” problem. Katie Johnston (CNFAIC’s 2014 Intern) and I were out yesterday on Tincan and had one of the largest collapses I have felt – ever. We put a hole in the snow to investigate and sure enough, found a 2″ thick layer of facets to be the culprit – more details on this
HERE. Collapsing was also reported from Magnum yesterday in lower angle terrain.

The tricky part of our current persistent slab problem is we are not finding this weak layer of facets everywhere. Because of the variable distribution and lack of information in many areas, this slab/weak layer combo is guilty until proven innocent. These avalanches have been occurring in fairly small pockets so far but have the potential to be larger in bigger terrain. They also have the potential to be triggered remotely, from ridgelines or under slopes. Avoidance of steep (over 35 degree) upper elevation starting zones and cross loaded gullies will be the best management tactic related to the problem.


Our friends at the Utah Avalanche Center recently posted this great video on what a persistent slab problem is and why it can be so tricky. If you have 7 minutes it’s a great watch.

Avalanche Problem 2
  • Wind Slabs
    Wind Slabs
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.
More info at Avalanche.org

Lingering wind slabs formed by the bump in Easterly wind on Friday may still be found today. Additionally, there could be a few areas with recent wind loading from a slight bump in wind last night. Keep an eye out for any area with old or new wind deposited snow. These wind slabs are likely to be 1-2′ thick and predominantly on South and West aspects. They also have the potential to step-down and trigger a persistent slab which would create a larger and more dangerous avalanche.

Image: Human triggered wind slab off the Tincan ridgeline (3,400′ SW facing – estimated 6-24″ deep, 50′ wide and running 300′).
Human triggered wind slab off the Tincan ridgeline (3,400' SW facing).

Additional Concern
  • Cornice
    Cornice
Cornice
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
More info at Avalanche.org

Cornices have been building, and falling, with February’s stormy weather. One party saw a remote/natural cornice fall yesterday on the Magnum Ridge after another party walked by. This is good reminder to always give cornices a wide berth. Keep in mind they can also trigger an avalanche below.

Loose snow avalanches:
Sluffs are likely to be easily initiated in steep terrain at all elevations due to the loose surface snow and possible 1-3″ of new light snow today.

Weather
Sun, February 16th, 2014

During the past 24-hours we have seen partly cloudy skies with a few instability ‘snow’ showers. Around an inch of snow has accumulated since last night. Winds have been light to moderate from the East (average 10mph with gusts to 30mph). Temperatures have averaged around 10F at all elevations with valley bottoms dropping to the single digits this morning.

Today, another round of off-and-on light snow showers will be over us with 1-3″ of snow possible. We may get a bit of visibility if we are lucky. Winds will be in the 10-15mph range from an Easterly direction on the ridgetops and temperatures look to rise to the low teens at the mid elevations and to ~10F on ridgetops.

The showery pattern that has been over us for the past several days looks to continue through tomorrow and clear up with mostly sunny skies Tuesday.

Observations
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Riding Areas
Updated Fri, May 01st, 2020

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
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
Closed

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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.