Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Wed, January 6th, 2021 - 7:00AM
Expires
Thu, January 7th, 2021 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger will be MODERATE above 1000′ today, where it is possible a person could trigger a wind slab avalanche up to a foot deep. Active weather today will bring a few inches of heavy snow with strong winds, building sensitive wind slabs on top of weak snow. Pay attention to indicators of unstable snow as snowfall and winds continue through today, and stick to low-angle terrain if you notice any cracking or collapsing in the snow around you, or any recent avalanches. The avalanche danger will remain LOW below 1000′.

Placer and Portage valleys: Heavier snowfall is expected to bring around a foot of new snow during the day at higher elevations near Portage and Placer, which will make larger human-triggered avalanches likely in these areas.

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Wed, January 6th, 2021
Alpine
Above 2,500'
Moderate (2)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
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
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Skiers triggered small avalanches up to 6″ deep on wind-loaded slopes on Notch Mtn. and in Eddies yesterday. These were not big enough to bury a person.

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

A storm system is bringing 2-4″ of heavy snow with strong winds, building sensitive wind slabs on top of low-density snow from the first part of this week. A fragile setup on its own, this upside-down combination is also sitting on top of various weak layers including surface hoar up to around 1700-2000’, and near-surface facets up to ridgetops. Today it will be possible for a person to trigger an avalanche up to a foot deep in wind-loaded areas below ridgetops and convex rollovers, or in cross-loaded gullies. Be sure to pay attention to clear signs of unstable snow like cracking, collapsing, and fresh slab avalanches as the active weather continues today. If you see any of these red flags, you can stay out of harm’s way by avoiding traveling on or below steep wind-loaded slopes. As of this morning, weather models are still mixed on the timing and amount of snowfall expected with this storm. Pay attention to changing conditions as it develops– if we do end up getting more snow, avalanche conditions will become more dangerous. The rain level is expected to rise later today and into tonight, but it should stay below 1000’.

Cornices: Give cornices plenty of space as they can break farther back than you might think. Be mindful while traveling below them, minimizing your time spent underneath them.

Loose Snow Avalanches: Be aware of loose snow avalanches in steep terrain. While it is not likely they would be big enough to bury you, they can pick up enough volume and momentum to carry you and can be a serious issue in consequential terrain. These will be dry snow for most elevations, but we could see some loose wet avalanches below 800 feet as the rain level moves up later today.

Small skier-triggered avalanche on Notch Mtn. Photo: Garth Schulz. 01.05.2021

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
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.
More info at Avalanche.org

The Dec. 1 rain crust/facet layer is buried 3-5’ deep, and appears to be weakest on the non-motorized side of Turnagain pass. It hasn’t gone anywhere, but with the current snowpack structure it is very unlikely a human could trigger an avalanche on this layer. We will continue to track this layer, but it will not be a major concern until we get a heavy load of snow or rain, or this weak layer becomes even weaker.

Weather
Wed, January 6th, 2021

Yesterday: After a brief snow shower in the morning, with rain up to around 500’, cloudy skies gradually broke up throughout the day. Easterly ridgetop winds were blowing 10-25 mph with gusts to 47 mph. Ridgetop temperatures rose to the mid- to upper 20’s during the day, with daytime highs in the low 30’s at lower elevations.

Today: We are expecting to see 2-4″ of heavy snow, with ridgetop temperatures in the mid-20’s F and highs reaching the low 30’s at lower elevations. Rain line is expected to stay around 500′ during the day today. Easterly ridgetop winds are expected to blow at 25-35 mph with gusts to 45 mph.

Tomorrow: Snowfall and strong winds will continue tonight, with another 6-9″ possible by tomorrow morning, and a few more inches possible during the day tomorrow. We are expecting sustained easterly winds at 30-40 mph at ridgetops starting tonight and continuing through tomorrow. Temperatures will stay in the mid- 20’s to low 30’s tonight, and the rain line is expected to move up to around 800′ overnight.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 29 0 0 74
Summit Lake (1400′) 28 0 0 30
Alyeska Mid (1700′) 30 2 0.15 78

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 NE 17* 46
Seattle Ridge (2400′) 24 SE 9 23

*Winds have been around 20-30 mph with gusts in the mid-30’s to mid-40’s since 3:00 a.m.

Observations
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Riding Areas
Updated Tue, January 12th, 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
Early season conditions exist, including thin ice on rivers, swamps and lakes. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Skookum Drainage
Open
Early season conditions exist, including thin ice on rivers, swamps and lakes. Please do not ride along Railroad tracks. Cross tracks at 90 degree angle and clear the right of way.
Turnagain Pass
Open
Twentymile
Closed
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.