Thu, December 01, 2022 Turnagain Pass Avalanche Forecast

Thu, December 1st, 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)

Recent Avalanches

The last known avalanche activity was small natural wind slabs triggered during the last outflow wind event 5 days ago.

Avalanche Problem 1

Wind Slabs
N E S W NW NE SE SW

Aspect/Elevation
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.

Aspect/Elevation of the Avalanche Problem

Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

Another round of NW outflow winds are impacting the forecast area today after a small refresh of 2″ of new snow overnight. This fresh snow combined with the soft surface snow that made it through the last round of winds this past weekend will be enough to create fresh wind slabs today up to 1′ deep. Wind slabs are most likely to form at upper elevations along ridgelines, cross loaded gullies, and convex terrain features. Human triggered avalanches will be possible today and natural avalanches unlikely.

We were pleasantly surprised yesterday that there was plenty of soft surface snow left over from the last round of outflow winds (ob here). It can be hard to tell just by looking at the snow surface where there are stiff wind slabs and where the snow surface is still soft. Stepping out of the skin track to feel the snow surface with your poles or feet is a great way to get a better sense of the surface conditions. Look for stiffer or hollow feeling snow at the surface to identify areas that have been wind loaded. Using small test slopes can be another good way to check whether fresh wind slabs are building up and if they are sensitive to human triggers in the area you want to ski or ride. As always, set yourself up for success by only exposing one member of your party to avalanche terrain at a time and spotting your partners.

Signs of recent wind transport on the snow surface from Tincan Common. The winds that created this texture occurred last weekend, but similar weather today will move the snow into fresh wind slabs at upper elevations. Photo 11.30.22

Avalanche Problem 2

Persistent Slabs
N E S W NW NE SE SW

Aspect/Elevation
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.

Aspect/Elevation of the Avalanche Problem

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

It has been over 2 weeks since the last known avalanches occurred on the layer of facets on the ground. However, we have not had a lot of snowfall to put stress on that weak layer in the past 2 weeks. At upper elevations (above 3000′) the snowpack remains thin in many areas and the facets on the ground appear to exist across the forecast area. It is tempting to disregard this weak layer since it has been so long since we have seen avalanches on it, but it is still possible to trigger a large avalanche on this layer at higher elevations. It is common for persistent weak layers like this to lay dormant for long periods and re-activate with the onset of significant new snowfall or rapid wind loading. Avalanches on this layer could be 1-3′ deep and would have high consequences if a person were involved.

Comparison of snowpack structure from upper elevations on Tincan. The weak layer exists in both locations but is better preserved and drier on the N aspect at higher elevation. Photo 11.30.22

Weather

Thu, December 1st, 2022

Yesterday: Clouds moved into the area during the daylight hours yesterday and there was a strong temperature inversion, with temperatures around 20 F at upper elevations and in the single digits at lower elevations. Winds were light during the day, then shifted to NW around midnight and increased in speed slightly with gusts up to 20 mph. We received about 2″ of fresh snow overnight across the region.

Today: Winds are expected to remain elevated through this afternoon with averages of 10-20 mph and gusts up to 30-40 mph. The winds will be stronger at higher elevations and along Turnagain Arm and other areas where gaps in the terrain allow outflow winds to flow toward the coast. Skies should clear up during the day today. Temperatures should remain in the teens to single digits.

Tomorrow: The outflow winds should start to back off overnight tonight and remain light on Friday. Temperatures will increase slightly with another inversion possibly setting up over the weekend. No new snowfall is expected through the weekend. Cloud cover should be mostly to partly sunny for the next few days.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	18	2	0.1	25
Summit Lake (1400′)	11	3	0.2	16
Alyeska Mid (1700′)	17	2.5	0.14	20
Bear Valley (Portage) (132′)	12	2	0.11	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	WNW	5	21
Seattle Ridge (2400′)	18	NNW	5	21

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
01/29/23	Turnagain	Observation: Tincan Backdoor	AAS-Level 1 1/27-1/30
01/28/23	Turnagain	Observation: Sunburst	Brooke Edwards
01/28/23	Turnagain	Avalanche: Seattle Ridge	W Wagner
01/28/23	Turnagain	Observation: Tincan Common	Tony Naciuk
01/27/23	Turnagain	Observation: Sunburst	John Sykes
01/27/23	Turnagain	Avalanche: Lynx Creek	Megan Guinn / W Wagner
01/25/23	Turnagain	Observation: Cornbiscuit	John Sykes Forecaster
01/22/23	Turnagain	Avalanche: Tincan	Schauer/ Guinn
01/21/23	Turnagain	Avalanche: Seattle Ridge	Elias Holt
01/21/23	Turnagain	Avalanche: Lynx drainage – avalanche	CNFAIC Staff

Riding Areas

Updated Fri, January 06th, 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	Open	Opened Dec 13th.
Placer River	Closed	Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Skookum Drainage	Closed	Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Turnagain Pass	Open	Opened Dec 13th.
Twentymile	Closed	Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Seward District
Carter Lake	Open	Opened Dec 13th.
Lost Lake Trail	Open	Opened Dec 13th.
Primrose Trail	Open	Opened Dec 13th.
Resurrection Pass Trail	Closed	Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor	Open	Opened Dec 13th.
South Fork Snow River Corridor	Open	Opened Dec 13th.
Summit Lake	Open	Opened Dec 13th.