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 5th, 2021 - 7:00AM
Expires
Tue, April 6th, 2021 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2,500′ where strong northwest winds are impacting the high terrain. Fresh wind slabs, up to a foot thick, are likely to form on leeward slopes. Any new wind slab will be likely to trigger and may release naturally in areas seeing the brunt of the winds. Below 2,500′ and on any slope not seeing wind effect, the danger is MODERATE. Triggering a slab breaking in old buried weak layers in the top few feet of the pack is still a concern. Pay attention to changing conditions and active wind loading.

SUMMIT LAKE/SNUG/LOST LAKE/SEWARD:  Strong northwest winds are impacting these regions as well. Natural wind slab avalanches are possible and human triggered wind slabs are likely. Wind slab avalanches will have the potential to step down into deeper weak layers, producing a larger avalanche.

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Mon, April 5th, 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)
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

The northwest winds are at it again. They are averaging this morning in the 20-25mph range and forecast to peak around midday near 30mph with stronger gusts. Despite the clear skies, these winds are bringing in single digit air and temperatures should stay quite chilly in the upper elevations. Lower, and even some mid elevations out of wind, could see enough daytime warming to melt the surface crusts, we’ll see.

The snow surface is quite variable and could sport a good amount of surface curst today in all but the mid and upper elevation shaded aspects. Yesterday’s warm snowfall event added 7-8″ of new moist snow in upper Girdwood Valley, 1-2″ at Turnagain Pass and 2-3″ in Summit Lake. Very warm afternoon temperatures melted southerly aspects (possibly to ridgetops) and likely some northerly aspects below 1,500′. How much soft dry surface snow is available for today’s winds to transport is the question.

Wind Slabs:  Watching for active wind loading will be key today, and fairly obvious. Wind slabs could form on a variety of aspects, including on top of slick sun crusts or other old hard layers making them even easier to trigger. They are likely to be in the foot thick category and relegated to the higher terrain. These winds can funnel through Turnagain’s non-motorized side from the south, if so, they may not find much snow to transport, limiting wind slab development here, but again something to watch for if headed out. Other than active wind loading, watch for cracks that shoot out from you and hollow feeling snow where stiff snow sits over softer snow.

Loose snow avalanches (sluffs):  If lower elevations warm enough this afternoon/evening, watch for wet sluffs on steep terrain features. Additionally, watch for dry sluffs on any shaded aspect with soft surface snow.

Seattle Ridge’s SE face, the road side, and the common motorized up-track. This slope is called Repeat Offender and the sun shining off the snow surface is a tell-tale sign a surface crust exists on this aspect. 4.3.21. Troy Tempel. 

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

As anyone who has been reading the forecast for a while now, we are still talking about a few layers of facets and buried surface hoar in the top three feet of the snowpack. It seems that the one or two layers in the top two feet or less are the ones that have been the most reactive, but these are getting harder to trigger. The most recent avalanches in these layers was a week ago in Summit Lake and over a week ago in Girdwood Valley. Shaded aspects, the ones that are most inviting with soft dry snow, are the most suspect place to trigger these now as southerly slopes have various sun crusts.

Knowing these layers are there, listening/feeling for whumpfing and watching for any other signs of instability are good things to keep in mind. As always, use good travel protocol, and consider the consequences if an avalanche does occur. Watch your partners, expose only one person at a time and know your save zones.

Snow pit from Notch Mtn area in upper Girdwood Valley two days ago, Saturday 4/3. Yesterday’s snow added 6-8″ on this surface. Two distinct layers of facets were found in the mid-elevations in the top two feet. These layers showed no signs of propagating, a good sign, but this is not the case everywhere. 

Weather
Mon, April 5th, 2021

Yesterday:  Snowfall was heavy for a brief period yesterday morning in Girdwood (~6″ fell in just over 4 hours, total in Girdwood 7-8″ by the afternoon). Turnagain Pass saw around 1-2″ and Summit Lake 2-3″. Rain/snow line rose to near 500′ in the afternoon when precipitation was tailing off. Ridgetop winds were strong from a south and westerly direction 15-25mph with gusts to 50mph on Sunburst. Temperatures rose to near 40F in the evening as skies cleared at sea level and 25F along ridgelines.

Today:  Clear, cold and windy. Skies cleared overnight and west to northwest winds picked up bringing in cold arctic air. We can expect ridgetops to see 25-35mph averages with stronger gusts. Temperatures should hit the single digits in the high elevations through the day while the lower elevations should remain in the 20’s-30’s with daytime warming.

Tomorrow:  Clear skies should remain through Wednesday. The northwest winds look to slowly decrease starting Tuesday and even more so on Wednesday. Temperatures should begin to warm back up as the winds let up.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) N/A 1-2 0.1 110
Summit Lake (1400′) N/A 2-3 .2 48
Alyeska Mid (1700′) 29 7 0.5 121

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 W 17 50
Seattle Ridge (2400′) 25 S 10 19
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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.