Mon, February 24, 2020 Turnagain Pass Avalanche Forecast

Mon, February 24th, 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

Both human and natural avalanches occurred in Summit Lake yesterday. A party skinning on the ridge of Manitoba remote triggered avalanches on the slope below and an impressive series of natural avalanches triggered by the northwest winds were observed on Fresno from the highway.

Remote triggered avalanches on Manitoba triggered by a party skinning on the ridge. 2.23.20. Photo: Carleton Lane

Crowns of the natural avalanches on Fresno seen from Manitoba. 2.23.20. Photo: Andy Moderow. See video in Avalanche Problem 1

Avalanche Problem 1

Deep Persistent Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic

Very Large

Large

Small

Size

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

Despite the lure of sunny skies and people starting to poke into avalanche terrain is imperative to keep the consequences of triggering a large avalanche in your mind today. It is still possible to trigger a deep, unsurvivable avalanche. This why we have issued the Special Avalanche Bulletin and why the avalanche danger remains at CONSIDERABLE. The travel advice advice associated with this danger level is the key to staying safe; cautious route-finding and conservative decision making are essential. Picture a large avalanche anywhere from 3-8+ feet deep on the piece of terrain you are thinking of traveling on. Before you head out today look at the observations from the past week and imagine triggering one of the avalanches pictured. Big thanks to everyone sending in information this weekend!

If you are headed out into avalanche terrain today, things to remember:

Between 3-8 + feet below your snowmachine or skis sits various layers of weak faceted (sugar) snow. This is why we have a deep persistent slab problem.
Direct sunshine is just starting to be a concern and could be a factor today. Slopes heating up later in the day may be easier to trigger. Watch for small roller balls from rocky areas.
In shallower snowpack zones such as Lynx Creek or Summit Lake, it could be much easier to initiate a large slab. As noted above there were both human triggered and natural avalanches in Summit Lake yesterday. Check out the video below.
Areas near rocks or shallower snowpack areas are likely trigger points. This could be hard to identify and why messing with a deep slab issue is such gamble.
Very large avalanches could be triggered that take out the entire slope and connect to adjacent slopes.
Many slopes have already slid but these could have portions still intact, just waiting for a trigger.
There is no way to know how close a slope is to avalanching. It could be the first person or the 15th person that hits the trigger point. Use safe travel protocol.
Remote triggering is possible (initiating a collapse in the weak layer from the top, side or bottom on the slope resulting in an avalanche) as was the case of the avalanche from the Manitoba skin track yesterday.
You can avoid exposure to this avalanche problem by remaining in the flats or on slopes 30 degrees or less with nothing steeper above.

Video Link: Fresno Basin Avalanche Procession 2_23_2020

Large avalanche in the Johnson Pass area seen from the air that likely occurred during the storm last week. 2.23.20. Photo: Graham Predeger.

Avalanche Problem 2

Wind Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic

Very Large

Large

Small

Size

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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 gusty NW winds created plumes off of the peaks, formed tender wind slabs and triggered avalanches in Summit Lake. Today it still possible to trigger a wind slab in steep wind loaded terrain. Northwest winds can be a bit funky and load from the south on the east side of Turnagain pass. Pay attention to wind hardened surface conditions. Look for drifting patterns and pillowed snow. Watch for cracking and listen for hollow sounding snow. Initiating a wind slab in the top couple feet of the snowpack could ‘step down’ and trigger a much larger slide that breaks in the deep weak layers discussed above.

Cornices: These have grown substantially over the past week and could be triggered today. Avoid travel on or underneath. Triggering a cornice fall could also initiate a deep slab on the slope below.

Loose snow avalanches: On slopes protected from the wind, soft snow may easily sluff in steep terrain.

Mid afternoon snow transport off Spirit Walker in Summit Lake. North winds transporting to the south. 2.23.20. Photo: Andy Moderow.

North winds pluming from the south on Tincan Ridge. 2.23.20.

Weather

Mon, February 24th, 2020

Yesterday: Skies were partly cloudy. Temperatures were in the single digits to low teens. Winds were northwesterly 10-20 mph gusting into the 30s. Overnight skies were mostly clear and temps dropped down to single digits and in some valley locations below 0°F. Northwest winds eased to 5-10 mph.

Today: Clear skies with temperatures in the single digits to high teens. Northwest wind 5-15 mph becoming calm overnight. Skies will be partly cloudy overnight and temperatures will be in the single digits and low teens.

Tomorrow: Skies will be mostly cloudy with snow starting in the late afternoon. Winds will start light and northwesterly and then shift to the east blowing 10-20 mph with gusts into the 30s. There is the potential for heavy snow and strong winds overnight into Wednesday with the storm ending Wednesday night.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	11	80
Summit Lake (1400′)	7	31
Alyeska Mid (1700′)	9	86

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	0	NW	10	30
Seattle Ridge (2400′)	5	*NA	*NA	*NA

*Seattle Ridge anemometer (wind sensor) is rimed over and not reporting.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/21/22	Turnagain	Avalanche: Magnum, Lipps and Tincan	CNFAIC Staff
05/17/22	Turnagain	Avalanche: Sunburst	CNFAIC Staff
05/17/22	Turnagain	Observation: Tincan Ridge	Joe Kurtak
05/11/22	Turnagain	Avalanche: Cornbiscuit and Magnum west faces	CNFAIC Staff Forecaster
05/07/22	Turnagain	Observation: Granddaddy	Kit Barton
04/29/22	Turnagain	Observation: Sunburst wx station	AS/ MM/ AM/ NH
04/28/22	Turnagain	Observation: More Turnagain Pass/Summit Lake wet slab activity	Alex Marienthal
04/27/22	Turnagain	Observation: Magnum	Sykes / Buttrick Forecaster
04/27/22	Turnagain	Observation: Girdwood/Summit/Turnagain Road obs	A S
04/24/22	Turnagain	Avalanche: Seattle Ridge – large glide avalanche on Repeat Offender path	CNFAIC Staff Forecaster

Riding Areas

Updated Fri, May 13th, 2022

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 as of May 1 per Forest Plan.
Placer River	Closed	Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage	Closed	Closed as of April 1st per Forest Plan.
Turnagain Pass	Open	Open. Extended opening through May 31.
Twentymile	Closed	Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake	Closed	Closed as of May 1 per Forest Plan.
Lost Lake Trail	Closed	Closed as of May 1 per Forest Plan.
Primrose Trail	Closed	Closed as of May 1 per Forest Plan.
Resurrection Pass Trail	Closed	Closed as of May 1 per Forest Plan.
Snug Harbor	Closed	Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor	Closed	Closed as of May 1 per Forest Plan.
Summit Lake	Closed	Closed as of May 1 per Forest Plan.