Thu, February 06, 2020 Turnagain Pass Avalanche Forecast

Thu, February 6th, 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)

Recent Avalanches

Over the past two days we know of 6 skier and/or snowmachine triggered slab avalanches from Girdwood, Turnagain Pass and Summit Lake. They have all been around 2′ thick. One triggered yesterday in the upper Girdwood Valley was just over 3′ thick. No one has been caught to date and several have been triggered remotely. All of these are failing on weak faceted snow 2-3′ below the surface. Many are being triggered in the mid-elevation band around 2,000′ and outside of wind effect.

Slab avalanche triggered Tuesday, Feb 4th. This slide was triggered at the crown and below the common skin track when a skier veered below the track to perform a stability test. Photo taken the day after on 2.5.20 by Jennifer Dematteis.

Slab avalanche triggered by second person on the slope. This is an example of slabs that are releasing in mid-elevation terrain and in the trees. Location: Pete’s North. 2.4.20. Photo: Leif Mjos

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

Triggering a dangerous slab avalanche that is large enough to bury, injure and kill a person remains likely. These slabs continue to release the minute folks venture off the beaten track and especially into areas that were not heavily trafficed in January. There was a bump in westerly wind last night, which could create some small wind slab issues in isolated areas today, but the main concern still lies deeper in the pack.

That said, we can’t let the clearing skis today sway our decisions in the backcountry. We are dealing with an unstable snowpack in the lower/mid elevations as well as the upper. Widespread collapsing (whumpfing) and several recent avalanches are clues we can’t ignore. The problem is, various weak layers of facets and buried surface hoar sit between 2-3′ below the snow surface. The slab on top is composed of either wind packed snow (wind loaded slopes) or settling and condensing snow due to the very warm temperatures. Either way, the slab on top of the weak layer(s) is showing it’s prime to avalanche and all slopes are suspect.

Some things to remember with this kind of avalanche problem:

Tracks on a slope do not make it safe. It could be the 2nd or 10th person that triggers the slab.
Remote triggering is possible. This means trigging a slide from below, the side or from on top.
Signs of instability may not be present before a slab releases.
Small slopes in the trees may avalanche.
Consider the consequences if the slope does slide. Is there a terrain trap you could be caught in?

This pit from Eric Roberts around 2,500′ on Eddies shows a failure just over 2 feet below the surface on buried surface hoar. The failure near the top of the snowpack is a shallow wind slab. The deeper weakness is clearly the more concerning in our situation now.

Weather

Thu, February 6th, 2020

Yesterday: Mostly cloudy skies were over the region yesterday. Temperatures were warm, in the mid 20’s°F along ridgetops and near 30°F in the mid and lower elevations. Ridgetop winds were light from the west (5mph) before picked up slightly overnight to the 10-15mph range.

Today: Mostly clear skies are forecast before another system pushes in tonight. Ridgetop winds should continue to blow from the west in the 10-15mph range before turning easterly tonight and increasing to the 15-25mph range. Temperatures are expected to stay in the mid-20’s°F with lower elevations bumping up to near 30°F during the day. Snowfall overnight could accumulate to 1-2″ by tomorrow morning.

Tomorrow: Cloudy skies, cooler temperatures and light snowfall is expected before a large storm system heads into the region Friday night and into Saturday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	29	0	0	56
Summit Lake (1400′)	27	0	0	20
Alyeska Mid (1700′)	29	1	0.05	56

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	23	W	7	27
Seattle Ridge (2400′)	26	*N/A	*N/A	*N/A

*Rime is covering parts of the Seattle Ridge wind sensor.

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.