Tue, April 10, 2018 Turnagain Pass Avalanche Forecast

Tue, April 10th, 2018

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Considerable (3)

Alpine Above 2,500'		Moderate (2)
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

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

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

Rain on snow breaks up bonds and adds load to the snowpack. Yesterday saw rain showers throughout today and the precipitation intensity picked up this morning. Rain continuing today combined with another day of warm temperatures and last night being the second night in a row with no freeze below 3000′ has increased the likelihood of both wet loose avalanches and wet slab avalanches. The snowpack will continue to get more saturated throughout the day. If you do decide to recreate today pay attention to the depth you are sinking in and get off the slope if the snow is over your boot tops or your machine is trenching in. Expect loose snow moving to entrain more as moves downhill. Yesterday observers reported large roller balls/pinwheels and the size of human triggered loose avalanches increasing later in the day. Anywhere that had softer drier snow becoming wet was the most tender.

Wet slab avalanches: We have not seen any wet slab avalanche activity yet, but it’s not out of the question that a wet loose slide (or the weight of a skier or snowachiner) could trigger a wet slab today as water penetrates to lower layers.

Wet loose avalanches on the North Corbiscuit chutes yesterday.

Wet loose avalanches on Pete’s South. Expect the size of wet loose avalanches to increase today.

Avalanche Problem 2

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

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

Above the rain line triggering a slab avalanche 1-2′ thick on North shaded aspects is still possible. Overall we have seen that the snow from last week has been bonding but haven’t forgotten that there is a weak layer under the old storm slab. The slab/facet combo remains suspect and may be more tender in the Alpine today as heavy wet snow falls. Wind loading may also add stress, as the ridgetop winds remain strong.

Facets found beneath last weeks storm snow in a pit on the North side of Tincan at 3,200′. Photo: Eric Roberts

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

It’s that time of year where the snowpack is warming up and cornices will begin to break. Give cornices a wide berth.

Weather

Tue, April 10th, 2018

Yesterday was mostly cloudy with rain showers throughout the day. Temperatures were in the 40Fs at sea level and the high 20Fs to mid 30Fs at upper elevations. Winds were easterly 20-30 mph gusting as high as 67 on Sunburst.

Today is forecast to mostly cloudy with around a half an inch of rain expected. Temperatures will remain in the 30Fs and 40Fs. Winds will continue from the east 15-25 mph with gusts into the 40s. Temperatures will stay warm overnight and rain showers will continue.

The next couple of days look to remain cloudy with a continued chance of rain as another low moves into the Gulf. There is a chance for some clearing this weekend but the long-term forecast discussion keeps temperatures warm and the overall pattern active. Springtime in AK!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	37	0	0.4	71
Summit Lake (1400′)	39	0	0.4	30
Alyeska Mid (1700′)	36	0	0.34	71

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	28	ENE	25	65
Seattle Ridge (2400′)	31	ESE	21	47

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.