Thu, November 26, 2020 Turnagain Pass Avalanche Forecast

Thu, November 26th, 2020

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Considerable (3)

Below Treeline
Below 1,000'

Moderate (2)

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

With another foot of snow falling yesterday, accompanied by very strong easterly winds, we are in a spooky spot today and tomorrow. There is the potential for a person on a snowmachine or skis to trigger a large, destructive avalanche. Unfortunately lurking beneath all this new snow are two buried weak layers. The storm on November 20th buried a layer of surface hoar mid-pack and there are weak (sugary) facets at the base. Both these layers produced large human triggered avalanches on Sunday. We have even more snow load now. Avalanches could break anywhere from 1-5′ deep, maybe even deeper.

With better visibility today and tomorrow it will be tempting to push it. It is crucial to keep it mellow and give the snowpack time to adjust. Be on the lookout for signs of instability. Recent avalanches, whumpfing/collapsing and shooting cracks are all indications that the snowpack is stressed. Ease into terrain. Avalanches could be triggered remotely today, from the side or below. In addition, it might not be the first rider or skier on the slope that triggers the avalanche. There may be tracks already and the 5 person out tips the balance. Choose terrain wisely, have escape routes planned and watch out for other groups in the area. Sticking to low angle slopes, and out from under larger slopes, is a great way to enjoy the new snow and make it home for some Thanksgiving dinner.

Four feet of snow on the ground at 1000′ means there could be avalanches 4′ deep or even deeper. It also means there is lots of fun to be had in lower angle terrain today, out of harm’s way. DOT stake. 11.25.20

Weak snow at the base of the snowpack is one of the main concerns today.

View of the Hippy Bowl remote triggered avalanche from 11.22.20. There is the potential for this type of avalanche today but even larger and more destructive.

Avalanche Problem 2

Storm Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

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

Yesterday’s storm was ‘upside down’. Snowfall started with slightly colder temperatures and then warmed up creating an 8-10″ layer of heavier snow over lighter snow. Today there is the potential for the denser layer to behave like a slab. In addition, the snowfall was accompanied by strong easterly winds. Keep your eyes peeled for areas winds have deposited snow, pillowed surfaces, stiffer wind packed snow and shooting cracks. Triggering a storm slab or wind slab avalanche in the upper layers of snowpack could step down and trigger a much larger avalanche that breaks in buried surface hoar mid-pack or in weak snow near the ground.

Snowpack @ 1000′ near moto-lot. The top layer shows Wednesday’s storm interface. The bottom layer shows buried surface hoar above a decomposing crust. 11.25.20

Weather

Thu, November 26th, 2020

Yesterday: Rain and snow throughout the day with rain/snow line around 500′. A foot of new snow (1.0″ SWE) fell across the advisory area. Winds were easterly 20-50 mph gusting into the 90s. Winds eased off in the in late afternoon. Temperatures were in the mid 20°Fs to mid 30°Fs. Overnight there were snow showers, easterly winds 10-20 mph with gusts into the 30s. Temperatures were in the high teens to high 20°Fs.

Today: Skies will be partly cloudy to mostly sunny and winds will be light and easterly. Temperatures will be in the high teens to high 20°Fs. Clouds will build in the evening with snow showers overnight and 2-5″ in the forecast. East winds 5-15 mph gusting into the 30s and temperatures in the 20°Fs.

Tomorrow: Skies will be partly cloudy and scattered snow showers are possible. Winds will be mostly calm and temperatures will remain in the 20°Fs. Another round of snow is on tap for Saturday. Fun quote from the NWS discussion this morning, ‘There is seemingly no end in sight to the supply of large deep storm systems traversing the Alaska region’. #snowtosealevelplease

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	7	1.0	44
Summit Lake (1400′)	31	6	0.6	17
Alyeska Mid (1700′)	31	13	0.9	48

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	NE	26	95
Seattle Ridge (2400′)	24	SE	10	85

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.