Wed, December 21, 2016 Turnagain Pass Avalanche Forecast

Wed, December 21st, 2016

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Low (1)

Below Treeline
Below 1,000'

Low (1)

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

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Avalanche Problem 1

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 touchy snowpack was that was observed over the weekend has calmed down as the new snow has settled and the snowpack is showing signs that it is adjusting. However, it is still very important to remember that the 12”-14” of new snow that accumulated incrementally fell onto suspect weak layers. A widespread layer of weak faceted snow remains our primary layer of concern and was the culprit in many skier triggered avalanches over the weekend. Monday, an observation from Sunburst showed propagation potential on a layer of buried surface hoar (buried Dec.15th) which is sitting on a wind hardened bed surface along some ridgelines. Slopes that were wind loaded due to the storm snow arriving with moderate to strong Easterly ridgetop winds have the most potential to be hazardous as the slabs are deeper and stiffer. Watch out for areas with hard over soft snow, wind pillows or drifts and be on the look out for obvious signs like cracking and whumpfing sounds. Steep unsupported slopes and areas with stiffer connected slab over the facets or buried surface hoar should be avoided. Triggering a dangerous slab avalanche is still possible with our current snowpack set-up.

Snow pit from Monday on Sunburst showing the December 15th layer of buried surface hoar. Photo: Heather Thamm

Avalanche Problem 2

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

“Sluff” may also be fast moving on steep terrain features where the snow is loose and unconsolidated. Be aware of terrain features that could have high consequences if knocked off your feet.

Additional Concern

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

Expect cornices to be sensitive and easy to break off. They also could trigger a slab avalanche below. If you choose to walk a ridgeline today, give these a wide berth and be aware of people below you.

A small piece of cornice fall pulled out the surface snow below yesterday in Zero Bowl.

Weather

Wed, December 21st, 2016

Yesterday was partly cloudy with afternoon sunshine. Temperatures were in the high teens and low 20Fs and winds were calm. Overnight temperatures and winds were similar.

Today and tonight will be mostly cloudy with a chance of snow. Winds will be light and northerly and temperatures will be in the 20Fs during the day dropping into the low teens/single digits overnight.

There is cooling and clearing trend for the remainder of the week with a chance for snow returning for the Holiday weekend.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	22	0	0	28
Summit Lake (1400′)	10	0	0	9
Alyeska Mid (1700′)	24	0	0	17

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	16	ENE	7	15
Seattle Ridge (2400′)	21	SE	3	6

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/28/22	Turnagain	Avalanche: Turnagain Pass – late May wet slab cycle	CNFAIC Staff
05/21/22	Turnagain	Avalanche: Magnum, Lipps and Tincan	CNFAIC Staff
05/17/22	Turnagain	Avalanche: Sunburst	CNFAIC Staff
05/17/22	Turnagain	Observation: Tincan Ridge	Joe Kurtak
05/11/22	Turnagain	Avalanche: Cornbiscuit and Magnum west faces	CNFAIC Staff Forecaster
05/07/22	Turnagain	Observation: Granddaddy	Kit Barton
04/29/22	Turnagain	Observation: Sunburst wx station	AS/ MM/ AM/ NH
04/28/22	Turnagain	Observation: More Turnagain Pass/Summit Lake wet slab activity	Alex Marienthal
04/27/22	Turnagain	Observation: Magnum	Sykes / Buttrick Forecaster
04/27/22	Turnagain	Observation: Girdwood/Summit/Turnagain Road obs	A S

Riding Areas

Updated Wed, June 01st, 2022

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 as of May 1 per Forest Plan.
Placer River	Closed	Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage	Closed	Closed as of April 1st per Forest Plan.
Turnagain Pass	Closed	Closed as of June 1st.
Twentymile	Closed	Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake	Closed	Closed as of May 1 per Forest Plan.
Lost Lake Trail	Closed	Closed as of May 1 per Forest Plan.
Primrose Trail	Closed	Closed as of May 1 per Forest Plan.
Resurrection Pass Trail	Closed	Closed as of May 1 per Forest Plan.
Snug Harbor	Closed	Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor	Closed	Closed as of May 1 per Forest Plan.
Summit Lake	Closed	Closed as of May 1 per Forest Plan.