Mon, December 19, 2022 Turnagain Pass Avalanche Forecast

Mon, December 19th, 2022

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		Moderate (2)
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

The last known significant avalanches occurred during and just after last week’s storm. This includes multiple avalanches that failed on weak layers buried deeper in the snowpack in Girdwood, the south end of Seattle Ridge, Lipp’s, and Pete’s North.

A relatively smaller avalanche failing in the new snow from last week triggered this deeper pocket on the north side of Lipps. This is on the smaller side of the avalanches that we saw fail on the deeper weak layers- some of which were 500′ wide or more. 12.18.2022

Avalanche Problem 1

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

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

The main concern for today is triggering an avalanche on weak, faceted snow associated with a crust that formed just before Thanksgiving, now buried around 2-4′ deep. Persistent weak layers like this are difficult to predict, and are common culprits in avalanche accidents. As we get farther out from our last significant loading event (now 4 days ago), the layer is becoming more stubborn, and we are seeing fewer warning signs of unstable snow. This doesn’t mean the problem is gone. We had multiple poor test results yesterday on Cornbiscuit (details), not far from where multiple other groups observed large collapses and shooting cracks over the weekend (details here and here). These are clear signs that the snowpack is still capable of avalanching. On the other hand, there are tracks all over steep terrain around Turnagain Pass, so we know that the likelihood of triggering an avalanche is decreasing overall. We suspect the most dangerous conditions are in the mountains closer to Girdwood, as well as on the south end of the pass. Both of these zones saw the most avalanche activity following the last storm.

The only way to manage a problem like this is by careful terrain management. Give yourself wide margins for error by avoiding steep, consequential terrain. This includes big, connected terrain features and steeper slopes above terrain traps like gullies, rocks, or trees. Ask yourself, what would happen if this slope were to avalanche? Persistent slab avalanches have a nasty tendency to release after there are multiple sets of tracks on a slope, or after a person gets way out into the middle of a slab.

Dry Loose Avalanches: With several days of clear, cold, and calm weather, there is plenty of soft snow on the surface. This will make dry loose avalanches (sluffs) likely in steep terrain. While these are unlikely to become big enough to bury a person, they can be dangerous if they carry you into terrain traps.

The poor structure in this snowpit is fairly consistent across the advisory area. Those test results highlighted in red suggest the snowpack is still capable of producing an avalanche. That is the layer we are concerned about. Photo: Andy Moderow. 12.18.2022

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Weather

Mon, December 19th, 2022

Yesterday: We had another day of clear, calm, and cold weather with temperatures struggling to get above 0 F in the valleys, but an inversion brought temperatures into the low teens F at higher elevations. Winds were light and variable, with no precipitation.

Today: Today is looking like another day of quiet weather, with high temperatures making it into the mid teens F and overnight lows getting back down into the single digits F. Winds should be light out of the east, with no precipitation during the day. We are expecting scattered clous, and there is a chance we might see some flurries tonight, but it shouldn’t be any significant precip.

Tomorrow: Cloud cover will build tonight into tomorrow, with light flurries possible and high temperatures in the low to mid teens F. Winds should be light out of the east to northeast. The next round of snow is looking to arrive Wednesday evening, with around 3-6″ overnight into Thursday.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	15	39
Summit Lake (1400′)	-3	28
Alyeska Mid (1700′)	13	42
Bear Valley- Portage (132′)	-4	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	9	W-E*	5	20
Seattle Ridge (2400′)	13	W-E	3	10

*Winds shifted directions around 6:00 p.m. yesterday.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
02/08/23	Turnagain	Observation: Eddie’s	Megan Guinn & John Sykes
02/07/23	Turnagain	Observation: Seattle Ridge	Wagner / Keeler Forecaster
02/07/23	Turnagain	Avalanche: Pete’s North	Megan Guinn
02/06/23	Other Regions	Observation: Johnson Pass to Bench Lake	Justin Siemens
02/05/23	Turnagain	Observation: Rookie Hill	Tony Naciuk
01/31/23	Turnagain	Observation: Johnson Pass area	Megan Guinn / W Wagner Forecaster
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

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.