Sat, December 15, 2012 Turnagain Pass Avalanche Forecast

Sat, December 15th, 2012

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		Moderate (2)
Treeline 1,000'-2,500'		Moderate (2)
Below Treeline Below 1,000'		Moderate (2)

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Avalanche Problem 1

Wind Slabs

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.

More info at Avalanche.org

Recent wind slab from Thursday is the primary concern. The worst areas will have a stiff layer of surface snow on top of very weak facets. This means above treeline in wind loaded zones including east facing slopes or pockets of wind slab in specific cross loaded terrain. The most obvious examples we have of this are the aspects easily visible from the highway of Seattle ridge in Turnagain Pass and Fresno ridge near Summit Lake. Both of these areas had large natural avalanches caused by wind loading. As time goes on, the likelihood of triggering similar slopes is diminishing, but the rate of stabilizing is slow due to the persistent nature of our weak layers.

There is no doubt in my mind that avalanches can be triggered today in the right terrain. Watch out for slopes steeper than 35 degrees and signs of recent wind loading. Avalanche size and destructive potential will be directly correlated to the size and consequences of the terrain.

Avalanche Problem 2

Persistent Slabs

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.

More info at Avalanche.org

The only change in the persistant weak layers in the last week is they are now buried by 1-2 feet of new snow. Which means that we now have heavier snow sitting on the extremely weak snow from the early season. When you add the wind loading component to the mix, it becomes a dangerous recipe. Yesterday we found frequent whumphing (collapsing) of the weak layers, telling us that they are tenuously carrying the stress of recent snowfall. That collapse would be the initiation of an avalanche if the slope was steep enough…

It’s good to remember that we don’t often deal with weak layers on the scale we currently see them. Our typical strong maritime snowpack has been replaced by a weak and shallow continental snowpack you would more often find in Colorado. This means that problems don’t diminish for days or weeks following a storm. The only way to ensure safe mountain travel when you find abnormally dangerous conditions is to stay in mellower terrain. We can’t go the same places we could in our normal stable snowpack and expect a positive outcome.

Check out this video from our colleagues in Utah for some good theory on terrain management.

Weather

Sat, December 15th, 2012

Mostly sunny this weekend with colder temperatures. We may see some stiff northwest wind in the mountains today. The next chance of snowfall is still a few days away.

The temperature inversion that gave us comfortable temperatures above treeline yesterday seems to be breaking down this morning. The coldest areas are showing lower single digit temperatures.

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).

Wendy will issue the next advisory Sunday morning, December 16th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/22/23	Turnagain	Avalanche: Tincan	Nick D'Alessio
05/12/23	Turnagain	Avalanche: Tincan, Sunburst, Magnum, Cornbiscuit	Heather Thamm
05/07/23	Turnagain	Observation: Tincan – Bear Tracks	CNFAIC Staff
05/05/23	Turnagain	Observation: Seattle Ridge	AS/ WW Forecaster
05/02/23	Turnagain	Observation: Cornbiscuit	Schauer/ Sturgess Forecaster
05/02/23	Turnagain	Observation: Seward Hwy Turnagain Pass	Joel Curtis
04/30/23	Turnagain	Observation: Magnum	Ayla, Kit Crosby, Barton
04/29/23	Turnagain	Observation: Tincan	John Sykes
04/28/23	Turnagain	Avalanche: Taylor Pass/Pastoral	Schauer/ Creighton Forecaster
04/28/23	Turnagain	Avalanche: Tincan	Andy Moderow

Riding Areas

Updated Thu, June 01st, 2023

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	Closed May 15.
Placer River	Closed	Closed May 15.
Skookum Drainage	Closed	Will close to motorized use on April 1, 2023 per the National Forest Plan.
Turnagain Pass	Closed	Will close on June 1.
Twentymile	Closed	Scheduled closure May 1.
Seward District
Carter Lake	Closed	Scheduled closure May 1.
Lost Lake Trail	Closed	Scheduled closure May 1.
Primrose Trail	Closed	Scheduled closure May 1.
Resurrection Pass Trail	Closed	Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor	Closed	Extended opening until May 15.
South Fork Snow River Corridor	Closed	Scheduled closure May 1.
Summit Lake	Closed	Scheduled closure May 1.