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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
Sun, February 24th, 2019 - 7:00AM
Expires
Mon, February 25th, 2019 - 7:00AM
Forecaster
Wendy Wagner
The Bottom Line

The avalanche danger is MODERATE on slopes over 35 degrees above 2,000′. Triggering an older wind slab resting on weaker faceted snow is possible. Slabs could be anywhere from 4″ to 2′ thick depending on prior windloading. Steep rocky terrain will be the most likely place to find one of these avalanches.  Additionally, sunshine with warm temperatures may cause wet sluffs on steep southerly terrain. As always, give cornices a wide berth and limit exposure under glide cracks.

GIRDWOOD / PORTAGE / PLACER:   Old wind slabs could be deeper, up to 2′ thick.

SUMMIT LAKE / JOHNSON PASS:    Triggering a larger, more dangerous slab remains a concern due to  various old weak layers in the mid and base of the snowpack.  Conservative terrain choices and a cautious mindset is advised  if choosing to venture into the further reaches of this area.

SEWARD / LOST LAKE:   Old wind slabs up to 2′ in depth could be found and triggered in this area on steep windloaded slopes.

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Sun, February 24th, 2019
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Low (1)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Moderate (2)
Treeline
1,000'-2,500'
Avalanche risk
Low (1)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • 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

After quite the pummeling by the outflow winds last week, the snowpack has had a couple days to rest under clear skies and light winds. As we head into today and into the work week, the quiet weather is expected to remain, allowing the snowpack to continue to adjust and stabilize. We have not heard of, or seen, any avalanche activity since Thursday when the NW wind event wreaked havoc. This event triggered large natural avalanches in the Summit Lake area on the Kenai as well as some other areas along Turnagain Arm and in the Portage Valley. The snow surface above treeline is a mixed bag of sastrugi, scoured areas, wind drifts, wind crust and wind slabs. That said, many areas are reported to still harbor soft fun snow and escaped the brunt of the damage.

The avalanche issues today revolve around older weak layers within the snowpack (persistent weak layers). The most recent weak layer was buried a week ago and sits around a foot deep under the wind affected snow and wind slabs. This layer has been showing signs that it could still be reactive but is on a downward trend. The second layer down is the MLK Jr buried surface hoar. This layer is showing signs of only being reactive in the Summit Lake zone. Also in the Summit Lake region is weak snow near the ground.

If you are headed out today watch for:

  • Wind slabs on steep slopes. Rocky terrain with unsupported slopes (i.e. steep slopes with a cliff underneath) are the most suspect for popping out a wind slab that may be sitting on weak snow.
  • Larger and more dangerous avalanches are possible in the Summit Lake and Johnson/Bench peak area where a thinner snowpack exists.
  • SUN EFFECT and moist/wet sluffs on steep rocky southerly terrain.
  • Cornices. Warmer high elevation temperatures can help loosen these monsters and with good days and ridgeline travel, don’t forget to give cornices a wide berth.
  • Keeping with safe travel protocol such as exposing one person at a time.


Make sure to check out Heather’s write up from the natural avalanche cycle on Fresno in the Summit area on 2/21. This event highlights the importance of matching avalanche terrain to the potential size of an avalanche. In this case, a portion of the fast moving debris overshot the main avalanche path and pushed up and over a subridge of hemlocks. 

For the snow geeks out there, a persistent weak layer round-up:

  • Valentine’s Layer:  Small faceted grains, 10″-16″ deep, last avalanches seen on this layer 2/21. Layer responsible for the 2/19 snowboarder remotely triggered slab on Seattle Ridge.
  • MLK Jr Layer:  Buried surface hoar, 2-3′ deep, last avalanches seen in this layer 2/21 in the Summit Lake region.
  • Basal facets (large faceted snow near the ground): This layer has only been found in the Summit Lake region and produced at least one very large avalanche on Thursday, 2/21.

 
Turnagain Pass’s beloved Tincan ridge yesterday, Saturday.

Additional Concern
  • Glide Avalanches
    Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
More info at Avalanche.org

New glide cracks are opening up around our region and some are filled in and apparently not opening up. The last known glide release was on the south side of Goat mountain in Girdwood Valley on Tuesday 2/19. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks. A short list of known cracks in popular zones:  Magnum, Lipps, Seattle Ridge, Eddies, Lynx Ck.

Small older wind slab on the lower SW shoulder of Lipps. Also, an old filled in glide crack is not easily seen, but the ‘crumpled’ up snow in the middle/lower portion of main slope is discernible. 

 

Weather
Sun, February 24th, 2019

Yesterday:   Sunny skies prevailed region-wide. Ridgetop winds were light from a generally westerly direction. Temperatures hit 30F at many lower elevations with ridgelines in the 20’sF. A strong inversion has set up again overnight with cold air pooling in valley bottoms and at sea level. This morning temperatures at the mid and upper elevations are in the mid 20’sF while valley bottoms and sea level temperatures are in the single digits.

Today:   Other than a possibility for some valley fog, today will be a carbon copy of yesterday. Sunny skies, light winds from the west and temperatures in the 25-30F range above the cold air trapped in valley bottoms. The cold air should mix out again in the afternoon warming parking lots and lower elevations to near 30F.

Tomorrow:   The ridge of high pressure over the region looks to remain in place through the work week and possibly into the weekend. Sunny skies, some chance for valley fog, cold temperatures in low-lying areas and warm temperatures at the higher elevations are to be expected. Don’t forget your sunglasses!

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25 0 0 61
Summit Lake (1400′) 15 0  0 30
Alyeska Mid (1700′) 24 0 0 57

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 W 4 9
Seattle Ridge (2400′) 27 Variable 2 5
Observations
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Riding Areas
Updated Mon, October 26th, 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
Johnson Pass
Closed
Placer River
Closed
Skookum Drainage
Closed
Turnagain Pass
Closed
Twentymile
Closed
Seward District
Carter Lake
Closed
Lost Lake Trail
Closed
Primrose Trail
Closed
Resurrection Pass Trail
Closed
Snug Harbor
Closed
South Fork Snow River Corridor
Closed
Summit Lake
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.