Sun, December 20, 2015 Turnagain Pass Avalanche Forecast

Sun, December 20th, 2015

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		Considerable (3)
Treeline 1,000'-2,500'		Considerable (3)
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

The storm continued on Turnagain pass yesterday depositing an additional 8+ inches during the day. There was a period where snow was falling over an inch/per hr. Easterly winds were strong enough to move the new snow around. There was very limited visibility and no opportunity to see if there was natural avalanche activity in the Alpine. Observers reported reactive storm slabs near treeline and shooting cracks in wind effected snow. Today the snowpack will need time to adjust after this new load. Look for signs of instability. Shooting cracks, whumpfing and recent avalanching all indicate that the snowpack is tender. Watch out for areas that have stiffer snow over soft snow and look for the patterns of wind loading. Leeward and cross loaded areas in steep terrain (35 degrees and steeper) have the most potential hazard today. Fresh cornices may break very easily and should be given a wide berth. Loose snow avalanches and soft storm slabs are also possible today in steep terrain. Watch out for terrain traps, gullies and depressions, where even a small slide can bury you very deeply. Don’t let clearing skies and fresh snow lure you into making poor decisions. Practice safe travel techniques: ride/ski slopes one at a time, stop in save zones, have escape routes planned and as always carry rescue gear!

Additional Concern

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

We continue to monitor the buried Surface Hoar and Near Surface Facets that sit over the Thanksgiving Rain Crust to 3000′ and over stiff old snow in the Alpine. These have been non-reactive in most tests on Turnagain Pass. Yesterday we couldn’t see into the upper elevation start zones to see if the new load triggered any deeper slabs (or storm slabs). We did find both grain types in our pit yesterday. This buried weak layer/bed surface combination is also a concern in the shallower Summit Lake snowpack. Signs are pointing to this becoming a non-issue but it is worth thinking about today. The snowpack has recieved a significant load and needs time to adjust. If the snowpack fails at this depth the slab could be deep and very dangerous.

Photo by Andy Moderow: Buried Surface Hoar intact and laid over.

Weather

Sun, December 20th, 2015

Yesterday’s storm brought an additional 8+ inches to Turnagain Pass, with high preciptation intensity for much of the day. The storm shut down much earlier in the Girdwood Valley and there was significantly less snow south of the Pass. Storm totals: Turnagain Pass 15-18″, Girdwood Valley 10-13″, Summit Lake 2-5.” Winds were Easterly and blew 20-30 mph gusting in the high 40s during the height of the storm. Temperatures ranged from the upper 20Fs to mid 30Fs with rain falling at sea level to approximately 800′.

Today will be partly cloudy to mostly sunny. Temperatures will be in the 20Fs and winds will be Northerly and light. Tonight will be mostly cloudy.

Tomorrow will be cloudy with a chance for scattered snow showers as a low in the Gulf pushes moisture into Southcentral. The Jet dips south later in the week and allows colder, drier air to move into the region over the holiday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	8	1.1	63
Summit Lake (1400′)	30	1	.1	19
Alyeska Mid (1700′)	30	3	.2	39

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	ENE	18	35
Seattle Ridge (2400′)	22	ESE*	10*	20*

*Seattle Ridge was only collecting wind data from 5am-4pm 12/19/15.

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 Mon, May 15th, 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	Open	Chugach NF staff will be assessing daily after May 15th. Please keep machines on the snow and avoid brown spots to keep this area open as long as possible.
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.