Fri, November 26, 2021 Turnagain Pass Avalanche Forecast

Fri, November 26th, 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)

Avalanche Problem 1

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

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

It is the old sugary snow with various layers of buried surface hoar that is sitting under all the new wonderful fluffy snow that’s the problem. At the lower and mid-elevations, it’s hard to discern that there would be any funny business 2-3′ below our feet – but unfortunately there is. In many areas folks have been traveling, that 2-3′ of new snow has been so light it’s just making for great powder turns and deep wallowing. But, as we found yesterday, getting into areas at the higher elevations and where the winds blew prior, the new snow isn’t as loose and is just cohesive enough to be a slab sitting on a weak layer. In short, the weak layer is guaranteed. It’s whether or not the snow on top is behaving like a slab. If so, we have a good chance at triggering a large avalanche, up to 2′ or more in depth if the slope is steep enough.

Paying close attention to any whumpfing in the snowpack or cracks in the snow surface that shoot out from us will be our main clues we’ve found a slab. Yesterday on Seattle Ridge my partner and I ventured to an area that had some wind effect several days ago and had not been traveled since the new snow. We had several large wumpfs and shooting cracks; it was a no brainer for us to stick to the more mellow slopes at that point. That said, there are slopes not showing these signs, mostly below the treeline, and it can be tough to know what is safe and what is not. When in doubt, we can just stick to slopes under 35 degrees with nothing steeper above us.

Safe travel protocols are key if choosing to get into steeper terrain. This is exposing only one person at at time, watching our partners closely, having an escape route planned if the snow does move.

Some other things to consider as we head into several days of clearing weather:

This issue is more pronounced in the higher elevations.
There is significant uncertainty in areas less traveled and in the motorized zone of Seattle Creek drainage (heads up to the snowmachiners this weekend).
Settlement can create a slab as the days go by. This is why it could be possible to trigger a slab in the mid and lower elevations. The caveat being, clear and cold weather should help keep the snow loose.
If traveling along a ridgeline, know that you could trigger an avalanche from above. Be aware of other groups that could be below you and in the path if that were to happen.

Area of large collapse (whumpf) and subsequent shooting cracks. This shooting crack was excavated to see where the weak layer was. Minus 1 Bowl (Warm-up Bowl) on Seattle Ridge 11.25.21.

To recap quickly storm totals (estimated due to precipitation sensors not always reporting data). This is from Monday night through Thanksgiving.
Turnagain Pass: 3o-34″ north end of Pass, 18-20″ south end
Girdwood Valley: 28 – 34″ storm total
Summit Lake: 3-6″ storm total

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

A handful of glide cracks are still opening around the region. We have not heard of a release into an avalanche for several days now, but we should still watch for cracks and limit any time under them as they truly are unpredictable and unsurvivable.

Weather

Fri, November 26th, 2021

Yesterday: Mostly cloudy skies with light snowfall here and there. Some clearing in the afternoon. Ridgetop winds were calm to very light from the northwest. Temperatures were in the 5-15F range.

Today: Mostly clear skies with some valley fog possible today. Ridgetop winds could bump up to 15mph from the northwest at times, but should remain mostly light in the majority of the forecast area. Temperatures are cooling back into the minus single digits at high elevations and the single digits in valley bottoms.

Tomorrow: Mostly sunny conditions are in store for the weekend, with possible valley fog. The northwest ridgetop winds look to remain fairly light as of now (5-15mph). Temperatures will also remain cold – single digits.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	12	5*	0.3*	64*
Summit Lake (1400′)	8	0	o	11*
Alyeska Mid (1700′)	12	N/A*	N/A*	N/A*

* Precipitation sensors are struggling to accurately capture the snowfall totals from the past few days.

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	6	W	4	14
Seattle Ridge (2400′)	6	N	3	10

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.