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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, March 11th, 2019 - 7:00AM
Expires
Tue, March 12th, 2019 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is  CONSIDERABLE  today.  Human triggered slab avalanches 2-3′ thick are likely on steep slopes and may be triggered remotely.  Careful snowpack evaluation, cautious route-finding and conservative decision-making are essential. Give cornices a wide berth and watch for wet snow moving in low elevation terrain.  

SUMMIT LAKE:   Despite only a few inches of new snow, this area has a very shallow and weak snowpack. Strong winds may have overload buried weak layers and caution is advised if heading to this area.

LOST LAKE:    Caution is advised in the Seward region. New snow and wind have created dangerous avalanche conditions. Large human triggered avalanches should be expected in this zone as well.

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Mon, March 11th, 2019
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Considerable (3)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Considerable (3)
Below Treeline
Below 1,000'
Avalanche risk
Considerable (3)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Triggering a large storm slab avalanche is still likely on steep slopes today and extra caution is advised. The snowpack still needs time to adjust to the recent load. The storm over the weekend brought 2-3 feet of snow and winds gusting above 100 mph. The snow fell on a variety of old snow surfaces including crusts, surface hoar and facets. There were a few natural avalanches that occurred during the storm reported yesterday. Observers in a couple of locations found the new snow bonding fairly well but overall there is still the potential for a large avalanche to be triggered. A few large whumpfs were experienced by groups in Turnagain and Summit Lake yesterday. Continued warm temperatures that can help the new snow bond to the old snow may first make the storm slab more cohesive and avalanches could be larger and more connected today. Wind-loaded areas are most suspect. High winds and heavy snow tend to make slabs lower down on the slope than expected, watch for pillowed areas and unusual loading.  The winds also created some mid-storm layers that were reactive and noted in observations. As temperatures rose yesterday the snow became wetter and heavier at lower elevations. Roller balls and wet sluffs/push-a-lanches may be possible today in steep low elevation terrain as there was no freeze overnight near sea level. Steer clear of cornices and choose terrain carefully. It may not be the first skier or snowmachine on the slope that triggers the avalanche and there is still the potential to trigger an avalanche remotely. 

Storm snow at 1500′ on Tincan yesterday. There was propagation at the new/old snow (small facets) interface, 3-10-19.

 Obvious wind-loading and cornice growth in Hippy Bowl, 3-10-19. 

 

Weather
Mon, March 11th, 2019

Yesterday: Broken skies, light rain/snow showers and easterly winds 10-20 mph with gusts into the 30s and 40s, easing off a bit mid-morning. Temperatures were in the 20Fs to mid 30Fs. Overnight mostly cloudy skies and easterly winds in the teens gusting to 30 mph. Temperatures stayed in the 20Fs and 30Fs.  

Today: Mostly cloudy skies with temperatures in the high 20Fs to high 30Fs. Snow and rain showers are forecast with a couple of inches of snow expected and rain/snow line around 1000 ft. Winds will be southerly 10-15 mph with gusts into the 20s and 30s. Temperatures look to cool overnight dropping into the teens and 20s.  

Tomorrow: Partly sunny with temperatures in the 20Fs and 30Fs. Chance of snow showers later in the day.   Light winds increasing overnight into Wednesday. The next storm looks to impact the area Wednesday evening.  

*Seattle Ridge wind sensor is not reporting.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′)  32 0    0 70  
Summit Lake (1400′)  33  0      0 27
Alyeska Mid (1700′)  32  0      0.25  71

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23   NE    15 49  
Seattle Ridge (2400′) 28   *N/A   *N/A   *N/A  
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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.