Tue, March 13, 2018 Turnagain Pass Avalanche Forecast

Tue, March 13th, 2018

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

Persistent Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Yesterday there were 3 reports of skiers and snowmachiners triggering avalanches across the region. A party of skiers triggered two avalanches on Sunburst, one on a deeper buried weak layer. The skier involved in the deeper avalanche was caught, carried, deployed their airbag and ended up off of the debris. A snowmachiner remotely triggered a slab in Grandview and a skier remotely triggered a slide from the skin track in Summit Lake. Today triggering a large and unmanageable slab avalanche 2-4′ thick remains our primary concern. Various layers of old faceted snow and buried surface hoar sit under the 2-4 feet of storm snow from Friday. These persistent weak layers have been well documented and are wide spread across our region. During the window of sunshine yesterday some folks ventured out into steeper terrain with no incident while at the same time others were triggering avalanches. Recreating in steeper terrain is a gamble at this point with high consequences if the house wins…

If you are headed out into the backcountry today things to keep in mind are:

The mountains are still adjusting to the several feet of new snow that fell four days ago and there is poor snowpack structure
Warming in the afternoon yesterday may also have played a factor in the avalanches being triggered. If the skies clear pay attention to changing conditions.
Avalanches can be triggered from the flats or remotely from an adjacent slope – be extra cautious to avoid being in a runout zone
Stick to slopes less than 30 degrees and ease into steeper terrain slowly. Evaluate the consequences if the slope releases; where will the debris go?
Listen for whumpfing (collapsing) in the snowpack, look for shooting cracks but realize you may not see signs of instability before the slope releases.

Sunburst avalanches from below. Photo: Conor Roland

Sunburst avalanches from a different view. The upper one is harder to pick out.

Grandview avalanche that was triggered from below, lookers left side. Photo: Sebastian Landry

Remotely triggered avalanche in Summit Lake. Photo Patrick McCormick

Additional Concern

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

Loose Wet Avalanches: Several inches of low-density snow fell this weekend. Wet snow or rain falling could trigger loose wet avalanche activity especially at lower elevations. Radiation from the sun, if it clears later in the afternoon, could also be factor today. Look for small loose wet sluffs on Southerly aspects in steep rocky terrain. On upper elevation slopes unaffected by rain, wind or sun loose dry avalanches (sluffs) are also possible in steep terrain.

Wind slabs: Shallow wind slabs formed on some leeward features yesterday due to moderate Easterly winds in the Alpine. Triggering a wind slab will likely be shallow, but could step down to a deeper layer of the snowpack and create a much larger and more dangerous avalanche.

Cornices: Cornices have grown and are suspect for breaking while traveling along ridgelines. Give these an extra wide berth and minimize any time below them. Cornice falls can trigger avalanches on slopes below.

Natural loose wet activity on Seattle Ridge in the afternoon yesterday.

Weather

Tue, March 13th, 2018

Yesterday was mostly cloudy in the morning and became mostly sunny by the mid to late afternoon. Temperatures were in the 20Fs to low 30Fs. Easterly winds were blowing 5-15 mph gusting into the 30s in the morning and calmed down in the afternoon. Overnight temperatures cooled slightly and then started rising in the early morning. Clouds moved in and Easterly winds were light.

Today will be mostly cloudy with snow/rain showers, 1-4″ of snow possible and rain below 800′. There is a chance of some clearing in the late afternoon. Temperatures will be in the high 20Fs to high 30Fs. Winds will be Easterly 5-15 mph with gusts into the 20s. It is forecast to be mostly cloudy overnight with a chance of snow showers.

Tomorrow looks to mostly cloudy in the morning with clearing in the afternoon, light Northwest wind and temperatures in the high 20Fs to mid 30Fs. The next system moves into the area Thursday. Timing and details are still uncertain.

*Seattle Ridge anemometer (wind sensor) rimed over and not reporting

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	29	1	0.1	90
Summit Lake (1400′)	27	1	0.1	36
Alyeska Mid (1700′)	28	1	0.12	82

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	ENE	14	38
Seattle Ridge (2400′)	23	n/a*	n/a*	n/a*

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.