Thu, January 16, 2020 Turnagain Pass Avalanche Forecast

Thu, January 16th, 2020

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
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

As we move farther and farther away from the New Year’s storm and the wind events of last week, the likelihood of triggering an avalanche is decreasing. The last human triggered avalanche was Friday evening(1.10.20) on the Crow Pass trail. However, our current persistent slab issue still warrants caution in the Alpine. Weak snow buried in the snowpack has the potential to be triggered especially where there is a hard slab sitting on top of weak facets “sugar snow”. Overall signs are pointing to improving stability but as your choose where to travel keep the lingering possibility of triggering an avalanche in mind. Pay attention to potential consequences. If the slope were to slide with you on it, where would the debris pile up? Watch for areas with very hard snow over soft snow and use safe travel protocols. Regions on the periphery of our forecast zone like Crow Pass or just outside the forecast zone like Summit Lake saw more wind effect last week and extra caution is advised.

Wind effect on Seattle Ridge, 1.15.20.

Weak faceted snow found below wind hardened surface snow in a snow pit on Fresno at 3000′, 1.15.20.

Additional Concern

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

Loose snow avalanches (sluffs): On slopes out of the wind expect sluffing in steep terrain. The surface snow is becoming looser and looser by the day with the cold temperatures.

Cornices: Give cornices plenty of space and limit your exposure when passing beneath them.

Glide avalanches: Due to the unpredictable potential to release, limit your time spent under glide cracks.

Cornices on the ridgeline and glide cracks opening just behind Manitoba, 1.15.20.

Weather

Thu, January 16th, 2020

Yesterday: Skies were mostly clear. Winds were light and variable and temperatures were inverted. Upper elevations were in the single digits and valley bottoms were a few degrees below 0°. Overnight the inversion remained in place and winds were calm.

Today: Clear skies continue to day with temperatures in the valleys ranging from just below 0° to the low single digits and upper elevations reaching highs in the teens. Winds are forecast to be mostly calm. Temperatures dip down again tonight and winds will be light and easterly.

Tomorrow: Another day of clear and cold with inverted temperatures and light east winds. Saturday a few clouds move in and build overnight into Sunday. Temperatures are forecast to rise into the 20°Fs and there looks to be the potential for some snow in the forecast.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	3	37
Summit Lake (1400′)	-6	15
Alyeska Mid (1700′)	3	36

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	4	E	7	21
Seattle Ridge (2400′)	6	variable	2	11

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.