Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Mon, April 12th, 2021 - 7:00AM
Expires
Tue, April 13th, 2021 - 7:00AM
Forecaster
Wendy Wagner
High Avalanche Danger
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

UPDATE at 9am:
The avalanche danger is HIGH above 1,000′ in the northern portion of our forecast zone (Girdwood Valley and Portage Valley). Upwards of 18-20″ of new snow and strong wind is creating dangerous avalanche conditions. Natural wind slab and storm snow avalanches are likely in this area. Pay close attention to new snow amounts and avoid avalanche terrain in any area seeing a foot or more of new snow.

A CONSIDERABLE danger exists everywhere else, including Turnagain Pass where 8-10″ of new snow has fallen. Natural wind slab avalanches are possible and human triggered wind slabs are likely.

PORTAGE VALLEY: There is potential for avalanche debris, from a slide occurring above, to run to low elevation terrain. Avoiding summer trails that run through avalanche runout zones, such as Byron Glacier trail, is recommended.

Roof Avalanches:  Rain and warmer temperatures could cause roofs to shed their snow. Pay special attention to children, pets and where you park your car.

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Mon, April 12th, 2021
Alpine
Above 2,500'
High (4)
Avalanche risk
Treeline
1,000'-2,500'
High (4)
Avalanche risk
Below Treeline
Below 1,000'
Considerable (3)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
High (4)
Treeline
1,000'-2,500'
Avalanche risk
High (4)
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
  • 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

After a long stretch of unseasonably cold, clear and windy weather, a warmer storm rolled in yesterday and is peaking this morning. This storm is bringing strong easterly winds and snowfall to between 500 and 800′; rain below this. As of 9am this morning the mid elevations around Girdwood have picked up 18-20″, Turnagain Pass 8-10″ and Summit Lake just a trace. Another 2-5″ is expected through this afternoon. These snowfall amounts are extremely variable and so will be the avalanche danger associated with them. East ridgetop winds have been averaging in the 40’s mph with gusts in the 70’s.

All the classic storm snow instabilities listed below will be today’s main concerns. The size of avalanches will be relative to the amount of new snow that falls. For example, larger avalanches, which are more likely to occur naturally, are expected near Girdwood and Portage valley with the higher snowfall totals. The one exception is if an avalanche steps down into buried weak layers, more on this in Problem #2. New snow is falling on a variety of surfaces, hard wind crusts, old sun crusts, softer snow over harder surfaces, etc. With the warmer temperatures, this can help the new snow to bond to the older snow more quickly, but that’s all to be determined. The next round of snow tomorrow night is likely to hit before any good bonding takes place.

Wind Slabs:  With such strong winds, wind slabs are likely to be releasing naturally in the higher terrain around Girdwood and may release naturally at Turnagain Pass. These could be up to 3′ thick near Girdwood and a foot plus thick at Turnagain Pass. Any new wind slab, regardless of size, should be easy for a person to trigger. Watching for cracks that shoot out from you and stiffer snow over softer snow are the red flags a slab has been found.

Cornices: These should have some new growth and pieces of them could release, triggering an avalanche below.

Storm Slabs:  This storm is coming in cold and leaving warm, creating an ‘upside down’ storm snow situation. This means heavier denser snow is falling on lighter drier snow, which can form a slab over a weak layer setup. Areas seeing close to a foot of new snow or more could see slab avalanches releasing in areas out of the winds and in the trees.

Loose Snow avalanches (sluffs):  Natural dry sluffs are likely to occur in steep terrain and off rocks in the mid and upper elevations.

Wet avalanches:  Low elevations seeing rain on the new snow (around 500′ and below) may see wet sluffs on steep terrain features. These areas are most likely in the Girdwood and Portage Valley areas where more precip is falling.

If you are headed out today, be extra cautious of where you are headed, how much snow has fallen and if there is avalanche terrain above you. Watch for cracking in the new snow and any signs the new snow is acting like a slab.

The National Weather Service snowfall total (ending today at 10am) looks to be coming true for Turnagain Pass, but higher amounts have already been seen in the upper Girdwood Valley. 

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

New snow, wind loading and warmer temperatures are all factors that can contribute to activating stubborn buried weak layers in the top 3 feet of the snowpack. Hence, avalanches in the new snow could step down to these layers and create a larger avalanche. The Crow Pass and Raggedtop area near Girdwood is a suspect region and has seen this occur over the past few weeks. Additionally, thinner snowpacks with more advanced weak layers are especially likely, such as in Summit Lake south of Turnagain Pass. Summit Lake may not see much snowfall, but the area is seeing strong winds and warming temperatures.

Weather
Mon, April 12th, 2021

Yesterday:  Cloudy skies, warming temperatures and strong easterly winds were over the area as a storm system moved in. Light snowfall began in the afternoon and picked up significantly overnight. Girdwood (1,700′) has seen almost 1″ of SWE and over a foot of new snow while Turnagain pass has seen around .5″ of SWE and ~6″ of new snow. Ridgetop winds have been averaging 35-45mph from the east with gusts as high as 75mph. Temperatures climbed to the mid 30’s F at sea level and low 20’sF along the ridgelines.

Today:  The storm looks to have just peaked early this morning and will slowly die off through the day. Cloudy skies with another 2-5″ of snowfall is expected by this afternoon with a rain/snow line climbing to near 800′. Ridgetop winds are forecast to be 25-35mph with gusts in the 40’s. Temperatures should continue to increase slightly to the upper 30’sF at sea level and the mid 20’s along the ridgelines.

Tomorrow:  A brief break between storms is expected late tonight through early tomorrow before the next, and more powerful, storm moves in. There may be some clearing skies tomorrow morning with light to moderate east winds. Winds and cloud cover should pick up tomorrow afternoon as this next storm arrives, peaking Wednesday. Stay tuned as an active weather pattern is forecast through the week.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 6-7 0.5 113
Summit Lake (1400′) 31 tr tr 48
Alyeska Mid (1700′) 28 16 1.0 128

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 NE 37 75
Seattle Ridge (2400′) 22 SE 20 37
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Riding Areas
Updated Tue, June 01st, 2021

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
It is packrafting and jetboat season!
Skookum Drainage
Closed
The Skookum Valley is closed to snowmachines. This closure occurs annually on April 1 as per the CNF Forest Plan.
Turnagain Pass
Closed
Closed as of June 1. 188 day season, that\'s a wrap!
Twentymile
Closed
It is packrafting and jetboat season!
Seward District
Carter Lake
Closed
Closes May 1.
Lost Lake Trail
Closed
Closes May 1.
Primrose Trail
Closed
Closes May 1.
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season. Will be open for moto use in the 21/22\\\' winter season as per the CNF Forest plan.
Snug Harbor
Closed
Closes May 16th.
South Fork Snow River Corridor
Closed
Closes May 1.
Summit Lake
Closed
Closes May 1.

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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.