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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 4th, 2020 - 7:00AM
Expires
Thu, March 5th, 2020 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger remains MODERATE and may rise to CONSIDERABLE tonight as northwest outflow winds impact the region. Watch for winds that could be actively moving snow. Wind slab avalanches around a foot thick will be possible to trigger on freshly loaded slopes. Additionally, triggering a very large avalanche breaking in weak snow 3-6 feet deep remains a concern region-wide.

SUMMIT LAKE TO SEWARD REGION:  Winds are expected to be strong in this area and a CONSIDERABLE danger applies. Natural wind slabs are possible and human triggered slabs are likely. Watch for blowing snow and loading slopes. Extra caution is advised.

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Wed, March 4th, 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

Outflow Winds… Strong northwest winds are seeping through from the interior and sending cold air over Southcentral. Where, when and how strong these winds will be are the driving factor for avalanches today and tomorrow. The one bit of good news is the winds are mostly splitting around Turnagain Pass. The Lost Lake and Seward zone is expected to see much stronger wind and Girdwood and Summit Lake are a bit of an unknown, yet could also see strong wind at times. Many of our ridgetop weather stations don’t pick up the northwest flow direction very well and it can be tough to determine areas impacted and areas that are not. For example the AKRR MP 43 weather station that sits near Bench Peak, above and to the west of Grandview, was gusting into the 40’s mph for a brief period last night. This location is just south of the advisory area.

Wind Slabs:  For today, skies should be clear enough to easily see if winds are transporting loose surface snow, loading slopes and sending any plumes off peaks or ridges. Keep in mind terrain can force the wind to swing around and blow from any direction. Other than witnessing active wind loading, watching for previous wind loading, stiff snow over softer snow and cracking in the snow around you are good ways to suss out wind slabs. A layer of buried surface hoar may be sitting under wind slabs, making them easier to trigger and possibly propagate further above or to the side than expected. 


This graphic shows forecast wind for 2pm today at the 4,500-5,000′ level (ridgetops). The color bar shows wind speed per color. Note how the winds are ushered down Cook Inlet and are less intense over Turnagain Pass. 

Cornices:  Small fresh cornice falls from winds today are possible in areas seeing significant wind. Most likely outside of the forecast zone.

Loose snow avalanches:  In areas out of the wind, sluffs are possible in steep terrain.

Sun effect:  The wind and cold temperatures should overrule any sun effect today.

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

Deeper in the snowpack and under all this wind slab business still sits various forms of weak faceted snow from January. These layers are buried between 3-6 feet deep and remain a concern for a person to trigger a very large and dangerous avalanche. As time goes by, the likelihood of triggering is decreasing, but we can’t assume we are out of the water yet. Areas outside our forecast zone to the south, with a shallower snowpack, are more likely to find one of these large slabs. Also, areas with little traffic this season are suspect. We need to keep our guard up and consider our terrain selection if getting onto steep slopes.

Weather
Wed, March 4th, 2020

Yesterday:  Mostly cloudy skies were over the region as very cold air pushed in from the northwest dropping temperatures to the single digits in most locations. Ridgetop NW winds increased overnight and have been in the 15-30mph with stronger gusts. Areas such as Portage Pass and the southern Kenai look to have seen significant northwest wind.

Today:  Clearing skies, cold temperatures and strong northwest outflow winds are expected over the region. Ridgetops are likely to see averages in the 10-20mph with areas favored by this flow direction between 30-40mph by this afternoon and may increase tonight. Temperatures look to remain cold (-5°F to 10°F) at all elevations.

Tomorrow:  Another day of clear skies and moderate to strong northwest outflow winds are forecast. Temperatures also stay cold, in the single digits. Warmer weather is headed in for the weekend and possibly a chance for additional snow.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 8 0 0 74
Summit Lake (1400′) 7 0 0 32
Alyeska Mid (1700′) 7 0 0 85

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) -3 W 8 17
Seattle Ridge (2400′) 0 NW 5 13

 

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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
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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.