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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
Mon, December 23rd, 2019 - 7:00AM
Expires
Tue, December 24th, 2019 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is MODERATE in the Alpine. Triggering small, tender wind slabs on steep leeward slopes and cross-loaded gullies is possible today. Watch your sluff in steep protected terrain and give cornices and glide cracks a wide berth.

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Mon, December 23rd, 2019
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
No Rating (0)
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
No Rating (0)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
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

Snow started falling yesterday afternoon and the region picked up 4-8″ of low density snow. Wind speeds also increased enough to transport snow at higher elevations in wind exposed terrain. Today expect small tender wind slabs just off of ridgelines and in cross-loaded gullies. The new snow fell covering the Solstice surface hoar. This sparkly snow grain now buried will likely become a layer of concern and will contribute to how touchy the fresh wind slabs are.  As you travel today look for cracking, be suspicious of loaded slopes and feel for hard over soft snow. If the slabs are stiff enough to support a person there may be some whumpfing as well.  This is a definite a sign of instability. Remember even a small slab can mean trouble in high consequence terrain.

Loose snow avalanches: In steep terrain that is protected from the wind, the new snow will increase the likelihood of sluffing. Observers prior to this quick shot of snow had already reported sluffs growing in size as surface snow became less cohesive with the cold temperatures.

Cornices:  An observer yesterday had some good insight into the cornice situation. “The cornices appear to be really precariously bonded.  They look as if they formed, then drooped but didn’t release… then a new cornice began to form above the old.  Really spooky looking and lots of tracks underneath them. With this wind they will get even worse.” Avoid travel on or underneath cornices. Watch for cornice crevasses and remember cornices can break much farther back than expected.

Sunburst weather station recording the northeast winds increasing yesterday and then decreased early this morning. 

Avalanche Problem 2
  • Glide Avalanches
    Glide Avalanches
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
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.

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

The more folks traveled around the region to this weekend, the more glide cracks were reported. These are starting to open in common areas to travel through. Remember to avoid spending time underneath. Glide avalanches are very unpredictable and can release at anytime.

Back of Cornbiscuit on far left, Superbowl to right out of frame, 12.22.19. Photo: Eric Parsons

Additional Concern
  • 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

In the high Alpine, above 3,000′, we have been tracking a weak layer of snow sitting near the base of the snowpack.  This weak layer is buried anywhere from 1-6+ feet deep due to the variable wind loading during the December storm cycles. There has been a lingering concern a person could trigger a large avalanche if they hit the wrong spot. Data is pointing to this layer being dormant as this point. However, we will keep it on the radar especially in areas where the overall snowpack is shallower – towards the southern end of Turnagain Pass, in Summit Lake and in the Crow Pass terrain north of Girdwood.

Weather
Mon, December 23rd, 2019

Yesterday: Skies were overcast and became obscured as the storm moved in. Light snow started in the early afternoon and easterly winds picked up mid-morning gusting into the 40s. Temperatures rose from single digits in the morning to 20°Fs by the afternoon. Snow continued overnight and winds decreased in the early morning.

Today: Cloudy skies and light snow showers with 1-5″ of snow forecast. Winds will be mostly light and easterly. Temperatures will be in the high teens to mid 20°Fs today and tonight.  Snow showers continue overnight and winds remain light and easterly.

Tomorrow: Cloudy skies and light snow continue. Temperatures stay in the 20°Fs and winds shift to the north and remain light. A white Christmas is in the forecast and the pattern stays active through the week!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 18 6 0.3 29
Summit Lake (1400′) 15 0 0 7
Alyeska Mid (1700′) 17 5 0.17 19

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12 NE 13 48
Seattle Ridge (2400′) NA* NA* NA* NA*

*Seattle Ridge was worked on yesterday and started reporting data but unfortunately may be rimed again.

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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
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Closed
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Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
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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.