Wed, March 09, 2022 Turnagain Pass Avalanche Forecast

Wed, March 9th, 2022

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

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

After a few days of sunny skies we are heading back into a stormy weather pattern. A weak low pressure system is forecast to produce 4-8″ of snowfall over the next two days in coastal areas (Girdwood, Portage, Placer) and closer to 1-3″ of new snow in Turnagain Pass. Winds are also expected to increase into the 15-25 mph range out of the southeast and redistribute the surface snow into fresh wind slabs. The primary avalanche problem today will be wind slabs up to 2′ deep which will be most likely at upper elevations along ridgelines, cross loaded gullies, and convex roll overs. The 1-3″ of new snow expected today will add some loose snow at the surface for the winds to redistribute.

The visibility could make it challenging to travel in areas seeing the most wind loading today, but keep an eye out for active wind transport, shooting cracks, and hollow feeling snow to locate fresh wind slabs if you get into alpine terrain. An added complication is that we have a variety of persistent weak layers in the upper snowpack that could become more active from the new snow and wind loading (check out problem 2 for more details). We recommend evaluating the terrain and snowpack carefully and being aware of the potential for avalanches to be remote triggered if you are in an area harboring persistent weak layers.

Winds expected to be stronger along the coast and Turnagain Arm today. Photo 3.9.22

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

The upper snowpack is harboring a variety of different persistent weak layers which were created about a week ago before the last significant snowfall. The most prominent are buried surface hoar and near surface facets which have both been found about 1′ deep in the snowpack in a variety of locations throughout the forecast area. The distribution of these weak layers is variable and the only way to know if they exist where you are travelling is by digging into the snowpack. Luckily they are not buried very deeply right now so this is a pretty easy task, but as the new snow starts to pile up on top of them it will get harder to locate the weak layers and the potential size of avalanches they could produce will increase.

There have been several observations of avalanches that were remote triggered or the person who triggered them was not the first on the slope (examples in Lynx Creek, Eddies, Seattle Ridge). These are classic signs of persistent weak layers and should be a warning sign moving forward. These weak layers might become more capable of producing avalanches with a new snow load or simply by wind creating a firmer slab on top.

Buried surface hoar underneath a soft slab on Tincan, this could become a larger issue once the slab is more cohesive (see ob here). Photo Kit Barton 3.7.22

Weather

Wed, March 9th, 2022

Yesterday: Mostly cloudy with temps in the mid to upper 30s at lower elevations and mid 20s at ridgetops. Winds were consistently in the 10-20 mph range with gusts between 20-30 mph. No significant new snow accumulation.

Today: Another storm system is moving into the area today with new snowfall totals of 1-3″ expected during the day. Snow totals should be on the higher end of that range in Girdwood, Portage, and Placer, with Turnagain Pass on the lower end. Snow line should be down to sea level today. Winds are forecast in the 15-25 mph range at upper elevations.

Tomorrow: More snowfall is expected overnight tonight and tomorrow, with storm totals from now to Thursday night between 1-3″ for Turnagain Pass and 4-8″ for Girdwood, Portage, and Placer. Snow line is expected to creep up to about 500′ tomorrow as the temperatures increase. Winds will increase slightly overnight, ranging from 20-30 mph at upper elevations.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	34	1	0.1	94
Summit Lake (1400′)	32	0	0	40
Alyeska Mid (1700′)	32	1	0.1	NA

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	ENE	15	37
Seattle Ridge (2400′)	26	SE	13	25

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.