Wed, November 24, 2021 Turnagain Pass Avalanche Forecast

Wed, November 24th, 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

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

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

Conditions will still be dangerous today after the surprise storm from yesterday. We received 12-14″ snow by late yesterday morning, and had around 4″ fall last night. Light snowfall is expected to continue to trickle in, bringing another 3 or 4″ throughout the day. Easterly ridgetop winds are expected to continue at 15-25 mph until they start to calm down and switch to the west midday. All of this means the weather machine is hard at work putting a lot of new snow on top of weak, sugary facets. It is likely a human could trigger an avalanche on these weak layers, which could be 2′ deep or deeper, especially on upper-elevation wind loaded slopes.

The weather will be relatively quiet today, but avalanche conditions will still be touchy. The light and fluffy storm snow will start to settle into a more cohesive slab, which might make it easier to trigger a storm slab avalanche today than it was yesterday. Today will be a day to be careful with your route finding, approaching steep terrain with caution. Pay attention to clear warning signs of instability like shooting cracks and fresh avalanche activity, and dial back your terrain accordingly.

Wind Slabs: Some higher elevation slopes will have fresh wind slabs on the surface, which will be extra sensitive. These will most likely be found immediately below ridgelines, convexities, or in gullies. It will be especially easy to trigger an avalanche on these wind loaded features.

Wendy discusses the storm slab problem in this video from Seattle Ridge yesterday:

Snowpit near the Seattle Ridge uptrack yesterday. 14″ of new snow is sitting on top of weak facets. 11.23.2021

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

Glide activity seems to have slowed down in the past few days, but that doesn’t mean the hazard is gone. Glide avalanches are hard to predict, and they involve the entire snowpack so they are large and very dangerous. Be on the lookout for glide cracks, and limit the time you spend traveling below them.

Weather

Wed, November 24th, 2021

Yesterday: Another 2″ snow fell yesterday morning, with 3-4″ overnight last night. Easterly ridgetop winds were blowing 20-30 mph with gusts as high as 50 mph, but winds were much lighter at mid and lower elevations. High temperatures reached the teens to low 20’s F during the day, and overnight lows were in the single digits F. Skies were mostly cloudy, with the occasional ray of sunshine poking through.

Today: Light snowfall will continue to trickle in, which might amount to another 3-4″ throughout the day. Easterly winds will continue to blow at 10-25 mph, approaching 30 mph at the higher ridgetops. Winds should ease off and switch to blow out of the west late in the afternoon. High temperatures are expected in the low teens, with lows in the single digits.

Tomorrow: Cold air will start to move back into the area tomorrow, with temperatures struggling to get out of the single digits F during the day and dropping below 0 F tomorrow night. Westerly winds should remain light at 5-10 mph, and skies will be mostly cloudy.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	14	N/A*	0.5	N/A*
Summit Lake (1400′)	7	tr	tr	11
Alyeska Mid (1700′)	12	3*	.1*	N/A*

*Sensors were not recording for part or all of the day. SWE and Snow totals are estimates.

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	9	ENE	16	50
Seattle Ridge (2400′)	9	E	7	21

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 Sat, September 23rd, 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	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Placer River	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Skookum Drainage	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Turnagain Pass	Closed	Scheduled opening on the Wednesday before Thanksgiving per Chugach National Forest plan. Subject to adequate snow cover.
Twentymile	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Seward District
Carter Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Lost Lake Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Primrose Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Resurrection Pass Trail	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Snug Harbor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
South Fork Snow River Corridor	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.
Summit Lake	Closed	Scheduled opening per Chugach National Forest plan December 1. Subject to adequate snow cover.