Sat, February 09, 2019 Turnagain Pass Avalanche Forecast

Sat, February 9th, 2019

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Low (1)

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

The MLK buried surface hoar roughly 1-3′ deep has been responsible for 13 human triggered avalanches over the past two weeks. The last one was three days ago on Eddies. On that day snowpack tests were pointing toward a stabilizing weak layer and then the 2′-3′ deep avalanche was triggered remotely from the ridge on a steep, unsupported slope. This avalanche illustrates that snow pit tests are unreliable for the current problem. Furthermore, no signs of instability have been seen in conjunction with several of the large human triggered avalanches on this layer.

This is a tricky situation if wanting to get on slopes over 35 degrees and have a safe day. Several tracks may be on a slope before it avalanches and slabs have been often triggered remotely from ridgelines. There are also many slopes that could in fact be stable, but unfortunately this problem is still a guilty until proven innocent situation.

What to keep in mind today:
1- This weak layer is widespread in the region and seems to be particularly suspect between 2000′-2500′ due to a melt-freeze crust associated with it.
2- Use safe travel protocol. Expose only one person at a time (this includes paying attention to other groups in the area), watch partners, stop in safe zones and be rescue ready.
3- Consider the consequences of an avalanche. Will the debris pile up deeply in a terrain trap or strain a person over cliffs and rocky terrain? Slopes with a fanning runout, spreading the debris, are more favorable for a positive outcome in the event of an avalanche.
4- As always, one can simply stick to slopes under 35 degrees with nothing steeper above to avoid the issue. Steep, connected, unsupported slopes are the most suspect!

Eddies remote triggered avalanche, 2-6-19.

The MLK buried surface hoar layer was easy to spot in a pit on Seattle Ridge, 2-7-19.

Avalanche Problem 2

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

CORNICES: Last weekend there was a large cornice fall triggered in upper Seattle Creek drainage. Cornices are looming large in some of the Alpine terrain. Give them an extra wide berth as they often break farther back than expected.

LOOSE SNOW AVALANCHES (dry and wet): Dry loose “sluffing” is possible in steep terrain. Daily warming and radiation from the sun could warm surface snow on steep Southerly aspects. Watch for roller balls and small wet-loose avalanches especially under rocky areas.

Corniced ridge and loose snow avalanches on Magnum back towards Super Bowl, 2-8-19.

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Glide cracks are moving and opening across the region again. The last glide crack to release into an avalanche was roughly a week ago in the Summit zone just north of Manitoba. Look out for glide cracks and limit exposure under them.

Glide cracks below PMS Bowl on Magnum, 2-8-19.

Weather

Sat, February 9th, 2019

Yesterday: Skies were partly to mostly cloudy with high overcast clouds. Winds were light and westerly and temperatures were in the 20Fs. No precipitation. Overnight temperatures dropped a little and winds remained light.

Today: Mostly cloudy skies and light winds. Temperatures will be in the 20Fs to low 30Fs. No precipitation forecast. Overnight easterly winds will bump up with gusts into the 20s.

Tomorrow: Mostly cloudy skies and snow showers throughout the day as a trough moves in from the west. Temperatures will be in the 20Fs and winds will be easterly 10-20 mph with gusts into the 30s. Monday looks to have a period of clearing before the next chance of snow Tuesday.

*The Seattle Ridge anemometer (wind sensor) was destroyed. We have a replacement on the way and it should be operational by mid February.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	0	0	58
Summit Lake (1400′)	20	0	0	25
Alyeska Mid (1700′)	29	0	0	51

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	26	W	3	18
Seattle Ridge (2400′)	29	*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.