Mon, December 19, 2016 Turnagain Pass Avalanche Forecast

Mon, December 19th, 2016

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

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.

More info at Avalanche.org

An exciting day was had in the backcountry yesterday. Both for weather and avalanches. It was a ‘rapid loading’ event as heavy snowfall from 6am till 5pm loaded slopes with medium density snow. Human triggered avalanches were numerous, yet we have not heard of anyone being caught up in these. From what we know, these slides were in “small terrain” which equates to smaller and more manageable avalanches. See all the reports sent in last night HERE – a big thanks to these folks for writing in!!

Yesterday’s snowfall totals:
Turnagain Pass: 6-8″
Girdwood Valley: 5-7″
Summit Lake: 4-10″

The snowpack is showing its hand and it’s not a good one. Weak faceted snow sits under a slab anywhere from 8-20+” thick. The slab is relatively soft and composed of yesterday’s new as well as the 4-8″ that fell during the end of last week. Strong winds have redistributed the snow above treeline and slabs will vary in depth and stiffness. Things to keep in mind today:

You are likely to trigger an avalanche on steeper slopes
You can trigger these from below or from the ridgeline
Facets are notorious for wide propagating slabs and remote triggering
Watch for obvious signs of instability (recent avalanches, cracking and collapsing)
Quick hand pits and poking the snow with your pole (away from a used up-track) are good ways to monitor the slab and weak snow underneath

If skies clear enough for travel outside of the trees, another thing to keep in mind:

Small terrain = small avalanches = relatively manageable
Larger terrain = larger avalanches = unmanageable

Photo: Crown of easily triggered 8″ slab avalanche that sympathetically triggered three more small slabs on the other side of the gully. If you look closely you can see one in the background. More on that in video below. This is the definition of a ‘touchy’ snowpack.

Photo: Soft slab avalanche into a terrain trap in the Tincan Trees (left side of photo). Small terrain – small avalanche. Thank you to Kakiko Ramos-Leon for the photo.

Photo: Remote triggered shallow slab avalanche on a rollover in the Eddies area, Andy Moderow.

Hopefully by this point you are convinced that once the visibility improves, very conservative travel is warranted in the backcountry. If you get out, please send us your photos and information – we will be monitoring the pack daily but your reports are invaluable!

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Expect cornices to be sensitive and easy to break off. They also are likely to trigger a slab avalanche below. If you choose to walk a ridgeline today, give these a wide berth and be aware of people below you.

Weather

Mon, December 19th, 2016

Yesterday was a bone fide storm day on Turnagain Pass. Heavy snowfall began in the morning and tapered off last night. See the snowfall and water numbers below. Ridgetop winds were strong, averaging in the 20’s mph with gusts into the 60’s. Temperatures were relatively warm; low 20’sF on ridgelines and 30F at 1,000′ in the parking lots.

Today we can expect partly clearing skies – to some degree – and a chance for localized instability showers. Another 1-2″ of snow could fall where these ‘showers’ take place. Temperatures will be slightly warmer, near 32F at 1,000′ and increase to the upper 20’s along the ridgelines. Ridgetop winds will be light, 5-10mph from a Westerly direction.

For this week, most of the weather is getting pushed South and we should see a mix between clearing skies and localized snow showers.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	26	7	0.7	30
Summit Lake (1400′)	26	2 (manual report 4+”)	0.2	10
Alyeska Mid (1700′)	28	4	0.4	20

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	NE	26	67
Seattle Ridge (2400′)	23	SE	18	42

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.