Mon, January 04, 2021 Turnagain Pass Avalanche Forecast

Mon, January 4th, 2021

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Moderate (2)

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

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Recent Avalanches

Skiers backed off of their objective near the south end of Seattle Ridge yesterday, noticing shooting cracks in a fresh, unsupported wind slab as they gained elevation.

Avalanche Problem 1

Wind Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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

Last night brought 1-2” of light snow to the mountains near Girdwood, leaving Turnagain Pass high and dry as of 5:00 this morning. With 6-8” more snow (equaling around 0.5” snow water equivalent) possible by early evening and easterly ridgetop winds blowing 15-20 mph, avalanche conditions are expected to become more dangerous through the day. At upper elevations where the snow and wind will be the most intense, it will become likely that a human could trigger an avalanche 1’ deep in new and wind-drifted snow.

This new snow is falling on mixed surfaces, with a layer of surface hoar up to 1000-2000’, near-surface facets up to the ridgetops, and some firm, wind-scoured surfaces at mid- to upper elevations. The combination of a fresh slab sitting on weak snow will mean dangerous avalanche conditions, making it possible that avalanches failing at the new/old snow interface could propagate wider than normal. Pay attention to clear signs of instability as the day progresses. Shooting cracks, collapsing, and new avalanche activity are all clear indicators that avalanche danger is increasing and it is time to move to low-angle terrain and avoid runout zones.

Cornices: New snow and winds are making cornices a little more sensitive today. As always, be sure to give them plenty of space as they can break farther back than you might think.

Sluffs: A few inches of low-density snow will be eager to move in steeper terrain. If you do decide to move into steeper slopes, be on the lookout for loose snow avalanches gaining momentum, especially as snow picks up this afternoon.

Yesterday’s surface hoar will be today’s weak layer. Pete’s North, 1600′. 01.03.2021

Avalanche Problem 2

Deep Persistent Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

The facet/crust combination from the Dec.1 rain event will be another concern today. While these storm totals are not enormous, a relatively small avalanche failing near the surface of the snowpack could provide a substantial load to a suspect layer in some parts of our forecast area, and there is a chance it could step down to create a large avalanche 3-5′ deep. This layer seems to be the weakest towards the south end of Turnagain pass, especially on the non-motorized side. This layer only exists up to about 2500’, and although it is unlikely to trigger an avalanche on this layer, we still cannot rule it out entirely.

The dark line in the middle of this snowpit is the 12/1 rain crust we have been talking about. While it is not a concern everywhere, it does seem to be harboring weak snow towards the south end of Turnagain Pass. Photo: Eric Roberts. 01.01.2021

Weather

Mon, January 4th, 2021

Yesterday: The day started off cold, with temperatures in the single digits F at valley bottoms and in the mid- teens at higher elevations, warming into the upper teens to low 20’s F. Cloud cover increased throughout the day, and winds were blowing 5-15 mph out of the east. Light snowfall last night brought 1-2” snow as of 5:00 this morning.

Today: Snowfall is expected to pick up around noon today, with periods of heavy snowfall expected this afternoon bringing 6-8″ snow equalling 0.5″ SWE by the end of the day. Easterly ridgetop winds are expected to pick up to 15-20 mph through the day, with gusts near 30 mph. We are expecting to see snow to sea level as high temperatures reach the mid-20’s F at lower elevations and upper teens F at higher elevations, with temperatures expected in the upper teens to upper 20’s tonight.

Tomorrow: Winds are expected to increase tomorrow, blowing 25-30 mph out of the east at the ridgetops. High temperatures will be in the high teens to low 20’s F. We should see a break in the snowfall tomorrow, with more to come later in the week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	21	0	0	74
Summit Lake (1400′)	14	1	0.1	30
Alyeska Mid (1700′)	23	1	0.06	79

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	17	NE	10	25
Seattle Ridge (2400′)	19	SE	10	19

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.