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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 9th, 2020 - 7:00AM
Expires
Tue, March 10th, 2020 - 7:00AM
Forecaster
Aleph Johnston-Bloom
The Bottom Line

The avalanche danger is MODERATE today at all elevations.  Triggering a wind slab around 1-2′ deep is possible in steep wind loaded terrain. Additionally, there is still a chance of triggering a deep persistent slab. Avoid travel on or underneath cornices and watch your sluff on steep protected slopes.

SUMMIT LAKE: South of Turnagain Pass the overall snowpack is shallower, with poor snowpack structure and was more affected by the outflow event last week. Triggering a large avalanche that breaks on weak faceted snow is possible. Extra caution is advised. Choose terrain carefully.

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Mon, March 9th, 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)
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

Winds today are forecast to be light and westerly and new wind slab formation is not likely during the day. The concern is triggering a wind slab that formed over the past couple days of easterly winds or an older one from the westerly outflow event last week. Wind slabs tend to heal up fairly soon after a wind loading event, especially with warmer temperatures. The question is whether this healing has happened or will these wind slabs actually stay reactive due to a buried layer of surface hoar and transition into a persistent slab issue. The wind slabs could be 1-2′ thick and will most likely be found in Alpine terrain on loaded slopes just off of the ridgelines and in gully features. As you travel in the mountains watch for signs of instability like cracking or collapsing. Steep terrain with hard wind affected snow over soft snow is the most suspect. Avoid terrain features with hard snow that look fat and loaded.

The question of the day is whether or not this weak interface on the buried surface hoar is an issue that heals up or lingers? 3.7. 20. Wolverine. Photo: Peter Wadsworth 

The surface hoar that was buried on Leap Day.

Cornices:  Avoid travel on or underneath cornices.

Loose snow avalanches:  In areas that were protected from the wind, sluffs are possible in steep terrain.

Sun effect: If the sun pokes out today look for signs of sun effect on steep solar aspects: moist surface snow, small roller balls or loose snow avalanches in protected spots, especially below rocky areas.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    Size
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and 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

There is nagging worry that someone will hit the wrong spot and trigger a very large avalanche on that fails on the weak faceted snow from January. This is still lurking 3 to 6 feet deep in the snowpack. The wind slab triggered in Lynx Creek last Thursday was a larger avalanche because it ‘stepped down’ into these old weak layers. As time passes the likelihood of triggering a deep slab is decreasing, i.e. is unlikely. However, the snowpack structure for this avalanche problem still exists and an outlier avalanche could be a nasty surprise. Areas that have a shallower snowpack are more concerning, places like Lynx Creek or Twin Peaks and south through Summit Lake.  As always, use good travel protocol and as you choose your route consider the consequences if a deep slab was triggered.

Weather
Mon, March 9th, 2020

Yesterday: Skies were cloudy and there were light snow showers throughout the day with around 1-6″ accumulating, favoring upper elevation Girdwood. Temperatures were in the high teens to low 20°Fs in the Alpine and the high 20°Fs to high 30°Fs at lower elevations. Winds were easterly 5-15 mph with gusts into the 30s. Overnight snow showers stopped, temperatures dipped slightly and winds became light.

Today: Skies will be mostly cloudy with a chance of snow showers and/or a pocket or two of clearing in the afternoon. Temperatures will in the high teens to high 20°Fs depending on elevation. Winds will be light and westerly during the day. As skies clear overnight and cooler air moves in, northwest outflow winds will start to pick up. Overnight lows will be in the single digits.

Tomorrow: Mostly sunny skies and temperatures in the teens. Winds will be northwesterly 15-25 with gusts into the 30s and 40s.  Winds look to peak during the day and then ease off overnight into Wednesday. Skies will be clear overnight with temperatures in the low single digits.  The forecast is for clear and sunny with an overall warming trend through the spring break week! Time to bust out the sunglasses and sunscreen!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 27 1 0.1 70
Summit Lake (1400′) 25 1 0.1 31
Alyeska Mid (1700′) 27 3 0.26 80

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 17 NE 10 33
Seattle Ridge (2400′) 22 E 7 19
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
Skookum Drainage
Closed
Turnagain Pass
Closed
Closed as of May 1. Thanks for a fun, safe season!
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Closed
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Closed
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Closed
Snug Harbor
Closed
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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.