Sun, February 21, 2016 Turnagain Pass Avalanche Forecast

Sun, February 21st, 2016

Alpine
Above 2,500'

High (4)

Treeline
1,000'-2,500'

High (4)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		High (4)
Treeline 1,000'-2,500'		High (4)
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

Storm Slabs

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Overnight a rapid loading event accompanied by strong Easterly winds has deposited over 24″ of new snow in the alpine and another 12-15″ is expected today. This snow has fallen on a weak pre-existing surface and large natural avalanche activity is very likely today and could easily run to the valley floor of Turnagain Pass. HUMAN TRIGGERED AVALANCHES up to 4’ thick WILL BE LIKELY on slopes steeper than 30 degrees. It will be extra important to give steep slide paths, like Seattle Ridge, a lot of space today. Do not put yourself in the way of a run out zone.

Wind Slabs: Natural wind slab avalanches up to 4’ thick are expected in the alpine elevations and could easily run the entire slide path. Yesterday wind loading was observed at all elevations and wind directions were confusing at lower elevations. Expect wind slabs to have formed on all aspects and elevations.

Storm Slabs: In areas protected from the wind, storm slabs up to 2’ thick could be easily triggered on steep terrain features and will be large enough to bury a person. Keep slope angles less than 30° and stay away from terrain traps.

Loose Snow: Sluffs due to heavy snowfall likely occurred last night and again will be likely today. These have the ability to trigger a slab avalanche on their way down.

Snowstake at Turnagain Pass over a 12 hour period shows over 2 feet of drifted snow.

Yesterday strong NE winds were observed at the beginning of the storm at mid to low elevations throughout Turnagain Pass

Avalanche Problem 2

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Cornice formations are extremely large and have received significant loading overnight. Natural cornice fall activity is anticipated today and will be an additional trigger of large natural avalanches.

Additional Concern

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

Glide Cracks litter Turnagain Pass between 1000’ to 2500’ and have received an additional load of snow overnight. These unpredictable hazards may release without warning today and could run further than expected. This is an additional reason to avoid being near a runout zone.

Weather

Sun, February 21st, 2016

Yesterday moderate Easterly ridgetop winds became strong in the afternoon with sustained speeds averaging in the 40’s mph and gusts in the 60’s mph. Over 24″ of new snow fell in the upper elevations and around 16″ along the road corridor. Temperatures have remained below freezing along Turnagain Pass (1000′) and rain/snow line is near 400′.

Today an additional 12-15″ of new snow is expected throughout the day, 1.0-1.25″ of snow water equivalent. Strong Easterly ridgetop winds will remain in the 30-40’s mph decreasing by late afternoon. Temperatures are expected to remain just below freezing at 1000′, but rain can be expected at sea level today.

By this evening winds and precipitation will decrease and temperatures will also cool slightly.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	23	2.0	123
Summit Lake (1400′)	32	11	0.5	41
Alyeska Mid (1700′)	31	21	1.92	105

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	ENE	40	76
Seattle Ridge (2400′)	26	SE	26	58

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 Sat, September 23rd, 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	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Placer River	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Skookum Drainage	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Turnagain Pass	Closed	Scheduled opening on the Wednesday before Thanksgiving per Chugach National Forest plan. Subject to adequate snow cover.
Twentymile	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Seward District
Carter Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Lost Lake Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Primrose Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Resurrection Pass Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Snug Harbor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
South Fork Snow River Corridor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Summit Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.