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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
Wed, March 18th, 2020 - 7:00AM
Expires
Thu, March 19th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

Today the avalanche danger is MODERATE with increasing northwest winds and clearing skies.  Pay attention to changing surface conditions. It will be possible to trigger small wind slabs on leeward aspects,  wet loose avalanches on protected solar aspects and dry loose avalanches on protected shaded aspects. As always give cornices and glide cracks a wide berth.

SUMMIT LAKE to SEWARD: Extra caution is advised. In much of this terrain the overall snowpack is thinner and triggering a large slab avalanche is possible due to a weaker snowpack. Increasing outflow winds today will impact these areas more. Watch for blowing snow and changing surface conditions.

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Wed, March 18th, 2020
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

Monday, March 16th there was a skier triggered D3 avalanche in West Groundhog Creek. This is located at the southern edge of the forecast area near Johnson Pass. The skier was caught, carried and partially buried. The slide was on a NE aspect at 4500′, ran 1200′ and was around 650′ wide. The crown was 1-2′ deep, with facets as the suspected weak layer. The snowpack was described as ‘thin’.

Skier triggered avalanche West Groundhog Creek. 3.16.20

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

There is a buffet of avalanche problems today, as there is variety of weather factors in the forecast and due to the nature of springtime avalanche conditions.  Overall what you encounter today should be fairly easy to manage and avalanches should be small.  However, the potential variety of problems and dynamic nature of springtime make paying attention to changing conditions crucial. Yesterday a couple of inches of snow fell and winds were easterly with gusts into the teens and low 20s.  Overnight the winds shifted to the west/northwest and will increase to 10-20 mph with gusts into the 30s. Watch for blowing snow and wind effect. This wind direction tends to impact places like Crow Pass and the south end of Turnagain Pass through Summit Lake to Seward the most. The wind could form small fresh wind slabs in the Alpine today. The snow yesterday fell on surface hoar and that could make these wind slabs quite touchy. Look for cracking and be cautious on steep wind loaded slopes, where even a small slab could take you for a nasty ride.

Surface hoar now buried by the couple of inches of snow on St. Patrick’s Day. This may make small wind slabs today easy to trigger. Photo: 3.15.20 on Maxs Mountain, Girdwood. 

Loose wet snow avalanches: As temperatures increase and the sun hits the few inches of new snow on steep solar aspects protected from the wind, watch for roller balls and small human triggered and natural loose snow avalanches. If these zones heat up enough to melt the sun crust underneath the new snow, these may entrain more snow and become more hazardous.

Small wet loose snow avalanches on a southwest slope, 2000’-2500’ near Silvertip. 3.16.20. Photo: Tim C

Loose dry snow avalanches:  Watch for dry snow sluffing on steep shaded, wind protected slopes.

Cornices: Give cornices a wide berth and limit your time traveling underneath them.

Glide cracks: Avoid travel below glide cracks. Remember these are totally unpredictable and could release at any time.

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

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

In areas with a thinner snowpack, including Crow Pass, the southern edge of the forecast zone and Summit lake, weak snow (both surface hoar and facets) is buried 1-2′ below the surface. Facets are the suspected weak layer in the large skier triggered avalanche mentioned above in recent avalanches. This setup continues to be a concern for these peripheral areas and extra caution is advised for triggering a large slab avalanche.

Weather
Wed, March 18th, 2020

Yesterday: Skies were cloudy with light snow showers starting in the afternoon with 1-2″ of accumulation. Temperatures were in the 20°Fs to mid 30°Fs. Winds were easterly 5-15 mph with gusts into the 20s. Overnight skies remained cloudy and temperatures were in the 20°Fs and low 30°Fs. Winds were light and easterly and then shifted to the west and increased early this morning.

Today: Skies will be partly cloudy becoming mostly clear by the evening. Temperatures will be in the mid 20°Fs to mid 30°Fs. Winds will be northwesterly 10-20 mph with gusts into the 30s. Tonight skies will be mostly clear with some patchy fog and temperatures in the 20°Fs and wind will become light and shift to the east.

Tomorrow: Skies will be partly to mostly cloudy with a chance of rain in the afternoon. Temperatures will be in the high 20°Fs to high 30°Fs. Winds will be light and easterly. Overnight there is chance of rain becoming a chance of snow with temperatures in the low 30°F to mid 20°Fs. Winds will be light and variable.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 2 0.2 67
Summit Lake (1400′) 28 1 0.2 31
Alyeska Mid (1700′) 28 2.6 0.19 78

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 24 E 5 19
Seattle Ridge (2400′) 24 SE 9 17
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
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Closed
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Closed
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Closed
Turnagain Pass
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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.