Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Fri, December 18th, 2020 - 7:00AM
Expires
Sat, December 19th, 2020 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

The avalanche danger remains MODERATE in the Alpine, above 2,500′. Watch for shallow new wind slabs that may have formed in yesterday’s slight bump in ridgetop winds. Additionally, on steep slopes with an overall thin snow cover, or a thin spot in the snowpack, there is still a chance a person could trigger a large avalanche breaking near the ground.

The avalanche danger is LOW at elevations below 2500’.

PLACER VALLEY/SKOOKUM: This zone has just opened to snowmachine use. Be aware that the snowpack is untested and extra caution is advised. Ease into big terrain, look for signs of instability and have escape routes planned.

SUMMIT LAKE: A thinner and weaker snowpack exists in this area. On steep rocky terrain above 2500′, there is still a chance a person could trigger a slab avalanche failing near the ground.

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Fri, December 18th, 2020
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
  • 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

The mountains received a few inches of new snow yesterday, just enough to begin hiding some of the old tracks. Along with this, ridgetop winds bumped up slightly midday for a period, averaging in the 10-20mph from the east. This may have moved a little snow around along the ridgetops and a few shallow wind slabs could be found in exposed areas today. These are likely to be small and in the 6-8″ thick range at most. This is a ‘Normal Caution’ avalanche issue to look for, along with remembering to give cornices a wide berth and watching our sluff on steep sustained slopes.

What isn’t a Normal Caution avalanche issue is our Deep Persistent Slab avalanche concern. As recently as yesterday, we are still getting snowpit results pointing to the weak October snow near the ground failing. Granted, it’s taking a lot of force to fail, and it’s not failing in many areas, which are all good signs that this problem is slowly going away…. But, if a person or snowmachine hits just the wrong spot, it is not out of the question that a large dangerous avalanche could be triggered. The most concerning areas are: (1) steep slopes with an overall thinner snowpack, such as the south end of Turnagain Pass, Johnson Pass, Lynx Cr, Silvertip and in Summit Lake, and (2) a thin spot in the slab in steep rocky terrain and on unsupported slopes. If choosing to travel in this type of terrain, extra caution is recommended; know there could be a weak layer under you, expose only one person at a time, have your partners keep a close eye on you and have escape routes planned.

A classic ‘gray-bird’ Alaskan day yesterday. This photo shows some wind effect along the top of Manitoba Pk in the Summit Lake area. 12.17.20. Caleb Rauch.

Weather
Fri, December 18th, 2020

Yesterday:  Overcast skies with light snow flurries were over the region. Most locations picked up around 2-3″ of very low density snow. Ridgetop winds increased into the 20’s mph during the day from the east with gusts to 32mph on Sunburst before quieting back down overnight. Temperatures were in the 20’sF at the mid and upper elevations.

Today:  Mostly cloudy skies should remain over the region with a trace of new snow possible. Ridgetop winds have shifted to the northwest this morning and should blow 5-10 mph today before decreasing tonight. Temperatures will stay cool, in the teens along the upper elevations and upper 20’sF at sea level.

Tomorrow:  A Special Weather Statement has been issued by the NWS for snowfall over much of Southcentral tomorrow. Only 3-6″ of snow is forecast from Girdwood to Seward, however it’s anticipated to effect vehicle traffic in many areas. Along with the snow, ridgetop winds should swing back around to the east and be relatively light, 10-20mph. Temperatures will remain cool, in the 20’sF at the lower elevations and teens at the higher elevations.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 21 2 0.2 61
Summit Lake (1400′) 21 1 0.1 25
Alyeska Mid (1700′) 19 2 0.2 61

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 E 12 32
Seattle Ridge (2400′) 19 SE 10 17
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Riding Areas
Updated Thu, April 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
Open
No parking in turnaround at end of the road near the outhouse.
Placer River
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
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
Open
Twentymile
Open
Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Seward District
Carter Lake
Open
Lost Lake Trail
Open
Primrose Trail
Open
Resurrection Pass Trail
Closed
Closed for the 2020/21 winter season.
Snug Harbor
Open
South Fork Snow River Corridor
Open
Summit Lake
Open

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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.