Sat, December 23, 2017 Turnagain Pass Avalanche Forecast

Sat, December 23rd, 2017

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

No Rating (0)

Alpine Above 2,500'		Considerable (3)
Treeline 1,000'-2,500'		Moderate (2)
Below Treeline Below 1,000'		No Rating (0)

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

Large plumes of blowing snow were present yesterday along all the tallest peaks around our region and strong Easterly winds are expected to continue today. Wind loaded snow could be on all aspects due to top loading and cross loading. These slabs will be hard and supportable and have the classic smooth pillow shaped look. Wind slabs could easily be located further down slope than expected and have the potential to fracture above you. Triggering even a small wind slab could have very high consequences especially in the upper elevations where there is also a potential for initiating a much larger and more dangerous deep slab avalanche. More on this below. Should you go into the upper elevations maintain a conservative mind-set and avoid big objective slopes including their runout zones.

Active wind loading as seen yestereday on Big Chief in the Seattle Creek area.

Variable surfaces are preseent throughout the alpine. Note the crossloading pattern including the pillowed shaped snow loaded along gullies on the SE aspect of Seattle Ridge

Avalanche Problem 2

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

On December 20th, two skiers were approaching Pastoral and remotely triggered a very large avalanche from below. Luckily they were able to run from its path and avoid being caught. This is a very scary set-up that is likely not going away soon. Deep slabs are located in the upper elevations of our forecast zone, above 3000’, on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facets. Observations over the last few weeks indicate this poor structure set-up is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart. Keep in mind:

Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks
Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
Thicker areas (3-5+’ thick) will be difficult trigger and several tracks may be on a slope before someone finds a trigger point
It is possible to trigger this avalanche from below and it could run further than expected
Large snow covered slopes that do not have piles of old debris under them are all suspect

Photo taken on Dec.21, the day after the Pastoral avalanche. Approximate route of where the party triggered this avalanche and retreated out of its way.

Photo taken on Dec.21st when strong winds started impacting our region. Note theNorthern Chutes on lookers left side have not avalanche yet and are actively loading snow.

For more info on the snowpack from this incident click HERE and more details about this avalanche click HERE.

Weather

Sat, December 23rd, 2017

Yesterday skis were partly cloudy with strong Easterly winds averaging in the mid 20’s with gusts in the 60’s. Warm air was observed at lower elevations mid to low 30F’s and temps in the mid 20F’s along ridgetops. No precipitation was recorded.

Today expect skies to be mostly sunny with Easterly winds elevated averaging in the 20’s with gusts in the 40’s. Day time temps at 1000′ are expected to be in the mid to low 30F’s and dip down to mid 20F’s overnight. High clouds are expected to move into our region tonight with a few flakes possible overnight.

Scattered snow showers are possible tomorrow, but little to no accumulation is expected. Temperatures are expected to range from 20F-30F. Winds should decrease tomorrow morning and remain Light from the East.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	0	0	31
Summit Lake (1400′)	25	0	0	11
Alyeska Mid (1700′)	32	0	0	26

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	ENE	27	69
Seattle Ridge (2400′)	28	ESE	20	51

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.