Wed, March 14, 2018 Turnagain Pass Avalanche Forecast

Wed, March 14th, 2018

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Considerable (3)

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

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

What happens when you mix rapid warming and buried weak layers??? March Madness? Welcome to spring…Yesterday was an interesting day for avalanches. The sun came out, temperatures rose (some weather stations recorded temperatures into the 40Fs), high clouds came in and the heat was trapped. This “greenhousing” is believed to have been the cause of a natural avalanche cycle that started mid day and peaked around 5 pm. The highlight of this was a large natural slab avalanche that was observed on an NE aspect of Skookum. This appears to have run on the mid January facet/crust combination that has been a layer of concern in mid elevation terrain. This layer seems to be the culprit in the majority of the avalanche activity since last week’s storm. What does this mean for today? We know that there is a slab approximately 2-4 feet thick over persistent weak layers that have been well documented and that are widespread across our region. Large avalanches can be triggered by the weight of a skier or snowmachiner, especially in a thinner spot near rocks or ridges. There were avalanches triggered on Monday. If the sun comes out today there is the potential that a similar warm up may happen and naturals will be possible. It is important to recognize that the snowpack can be even more unstable as warm air and solar radiation affect cold snow and buried weak layers. Extra caution is advised.

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

Several feet of new snow fell last week on buried weak layers. There is poor snowpack structure. If triggered avalanches could be large and very dangerous.
If the skies clear pay attention to changing conditions. Solar radiation and warm air temperatures can quickly make the snowpack more unstable. Natural avalanches will be possible.
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?
Realize you may not see signs of instability before the slope releases.

Natural slab avalanche in Skookum that released around 5 pm.

Natural slab on Seattle Ridge that releases around 1 pm.

Crown of one of the skier triggered Sunburst avalanches that occcurred Monday.

Mid elevation layer of concern: buried facets over a melt freeze crust.

Avalanche Problem 2

Wet Loose
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Size of Avalanches

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

Solar radiation and warm temperatures yesterday caused widespread wet loose avalanches. Some of these also triggered slabs on Southerly and Easterly slopes. If the sun comes out today pay attention to changing conditions. Naturals may run and could surprise you in the wrong spot. Wet loose avalanches may also be triggered from your skis or snowmachine in steep terrain on the solar aspects.

Natural wet loose avalanches and a slab avalanche on Seattle Ridge yesterday

Additional Concern

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: 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.

Wind slabs: Shallow wind slabs formed on some leeward features Monday 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.

Weather

Wed, March 14th, 2018

Yesterday skies cleared earlier than forecasted and the sun came out. High clouds built in the afternoon.Temperatures rose into the low 30Fs to mid 40Fs. Winds were Easterly 5-15 mph gusting into the 30s. Skies became cloudy overnight and temperatures dropped into the 20Fs and low 30Fs. Winds shifted to the west and were light.

Today will be mostly cloudy in the morning but could become sunny in the afternoon. There is a chance of snow showers in the morning. Winds are forecast to be light and Northwesterly. Temperatures will be in the 20Fs to high 30Fs. Tonight will be mostly cloudy with temperatures in the 20Fs to low 30Fs and calm winds.

Tomorrow the next system approaches form the Southwest bringing snow showers in the afternoon and increasing winds. Snow is in the forecast into Friday. Stay tuned for snow amounts. The NWS described a persistent unsettled pattern continuing into next week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	35	0	0	87
Summit Lake (1400′)	30	0	0	35
Alyeska Mid (1700′)	34	1	.11	79

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	E-W	9	34
Seattle Ridge (2400′)	29	E	10	32

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.