Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, March 27th, 2021 - 7:00AM
Expires
Sun, March 28th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is MODERATE this morning and expected to rise to CONSIDERABLE above 2,500′ by this afternoon due to a strong northwest wind event peaking tonight. Later today, natural wind slab avalanches will be possible and human triggered fresh wind slabs will be likely. Watch for active wind loading and avoid slopes and cross-loaded gullies with fresh wind deposited snow. In areas out of the wind, dry sluffs are likely on shaded slopes while daytime warming may soften surface crusts enough for wet sluffs on southerly slopes. Lastly, there is still a chance a larger avalanche could be triggered at any elevation due to buried weak layers in the top 3 feet of the snowpack.

SUMMIT LAKE/SNUG/LOST LAKE/SEWARD:  Stronger NW winds are forecast for these zones and natural wind slab avalanches are expected. Additionally, slabs may step down into buried weak layers and create a larger avalanche.

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Sat, March 27th, 2021
Alpine
Above 2,500'
Considerable (3)
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
Considerable (3)
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

Solar radiation from yesterday’s sunshine initiated many wet loose avalanches on steep southerly facing terrain. These all appeared to be composed of Thursday’s 6-8″ of new snow. Human triggered sluffs on shaded aspects also were very common yesterday along with a few sluffs that pulled out small shallow storm snow slabs and one small human triggered slab. There were 2 larger avalanche events:

Tri Tip (NW aspect at 2,700′):  In the Summit Lake area there was a close call with a skier caught in a slab avalanche up to 20″ deep and 100′ wide. The skier was ascending when the slab released 50′ above them. The skier tried skinning out of the way and was able to remove one ski before being caught and carried for 250′. The skier was partially buried with head above the snow and uninjured. Thank you to the group for sharing their experience and we are very thankful everyone is OK. Please take a minute to read their report HERE.

Raggedtop (NE aspect 3,600′):  Natural avalanches were noted in the NE bowl of Raggedtop yesterday. One large avalanche appeared to be fresh and may have released yesterday morning with early sunshine triggering a loose snow avalanche off the rocks, which triggered a slab avalanche lower on the slope, and then stepped down to buried weak layers and triggered larger slabs. See photos below in Problem #2.

Skier triggered avalanche on Tri Tip, 2,700′ on a NW aspect in the Summit Lake area. Photo taken 3.26.21 by Mike Davidson from the highway below.

 

Closer view of Tri Tip avalanche taken from the party involved. 3.26.21.

 

Natural sluffs that occurred during Thursday’s new snow can be seen in the middle of the photo. Also note the small slab that released mid-slope in the shade by a skier. Skier was able to easily ski off the slab. 3.26.21 Ryan Smeeding.

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

Another northwest wind event is on the horizon. As has been the case this season, these winds are likely to impact areas south of Turnagain Pass the most, but looking at the models, Turnagain may not get so lucky this time. Expect the winds to be on the rise through the day and by 6pm could be averaging 25-30mph along the ridgelines at Turnagain Pass. This flow direction often channels through Turnagain from the south along the non-motorized ridges while it remains westerly along Seattle Ridge. The bottom line however is wind slabs are likely to form on a variety of aspects later today.

There is plenty of soft surface snow to blow around, especially on the shady aspects that were not hit by the sun yesterday. Any new slabs could be quite touchy and up to a foot thick or thicker in areas with sustained winds for several hours. How quickly the wind will start forming slabs is a bit of a question, but I’d bet by the early afternoon; especially in the Summit Lake area.

Watch for active wind loading, which should be easy today, and avoid any slope or cross-loaded gully with fresh wind deposited snow. Shooting cracks will be good clues as well as signs of stiffer snow over softer snow. New wind loading could also overload buried weak layers and create a larger avalanche, similar to the avalanche triggered yesterday in the Summit Lake area. Although sun crusts are likely to be found on southerly slopes, winds could still be strong enough to load these aspects.

 

Forecast NW winds around 3,000′ today at 6pm. Wind speeds are represented by colors. This is Windy.com’s display of the NAM (North American Mesoscale) weather modeled winds.

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

There is still a concern of finding a slope where old buried weak layers (facets and buried surface hoar) are still reactive. The natural avalanches on Raggedtop and the skier triggered slab on Tri Tip are unfortunately good examples of what we are talking about. These slabs appear to have all or parts of the avalanches breaking deeper into old weak layers. Girdwood Valley and Summit Lake seem to be the two places most suspect for this type of avalanche.

After some new snow on Thursday and winds today adding stress to these layers, there is still a possibility a person could trigger one of these persistent slab avalanches. Be on the lookout for areas that were previously wind loaded and those with any new wind loading. The most suspect terrain will likely be at upper and mid elevations, especially immediately below ridgelines, in cross-loaded gullies, and below convexities. As always, watch for signs of instability, use good travel protocol, and think about terrain consequences. This type of avalanche issue might allow you to get well out on the slope before the avalanche releases and it might not be the first person that triggers the avalanche.

Raggedtop natural avalanche. Note the point release sluffs off the rocks that in turn triggered several slabs, some of which look to have stepped down to old buried weak layers. 3.26.21 Ryan Smeeding.

Wider view of avalanche and debris. 3.26.21 Ryan Smeeding.

Weather
Sat, March 27th, 2021
Yesterday:  Sunny skies and light west to northwest winds were over the region. Temperatures remained in the low teens along ridgelines and warmed significantly, to near 32F at the mid elevations and 35F at sea level. Today:  Mostly sunny skies with an increase in chilly northwest winds through the day are forecast. Ridgetop winds are light, 5-10mph this morning, and expected to climb to 25-30mph by 6pm and up to 35mph overnight tonight. Temperatures should not rise as much as yesterday due to the breezy conditions and remain in the teens along ridgelines and in the 20'sF at the mid elevations. Tomorrow:  Mostly clear skies should persist until tomorrow afternoon when another Bering low pushes in from the west. The northwesterly winds should dissipate on Sunday and turn southwesterly with the clouds late in the day. This system looks a lot like Thursday's and we may squeak another 4-8" out of it on Monday. Stay tuned. PRECIPITATION 24-hour data (6am - 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880') 26 0 0 113
Summit Lake (1400') 20 0 0 49
Alyeska Mid (1700') 26 0 0 119
RIDGETOP 24-hour data (6am - 6am)
Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812') 12 W 7 15
Seattle Ridge (2400') 22 NW 3 12
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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.