Sun, December 08, 2019 Turnagain Pass Avalanche Forecast

Sun, December 8th, 2019

Alpine
Above 2,500'

Considerable (3)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

No Rating (0)

Alpine Above 2,500'		Considerable (3)
Treeline 1,000'-2,500'		Moderate (2)
Below Treeline Below 1,000'		No Rating (0)

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

Recent Avalanches

Yesterday’s storm peaked late in the day and favored the Portage area where over 3″of rain fell in 24 hours. This equates to roughly 3 feet of snow along the peaks in Portage Valley and due to the rapid loading and strong winds, natural avalanche activity did result in the area (photo below). In the Girdwood Valley, 1-1.5″ of rain was recorded (estimated 10-15″ snow above 2,500′), while Turnagain Pass only picked up around .8″ of rain (roughly 8″ new snow) and Summit Lake .3″ rain (~3″ snow). The snow line rose from 1,000′ to ~2,000′ as temperatures spiked overnight to 40F at 1,000′.

Portage Valley, Five Sisters slide path. Debris from an avalanche releasing above makes it close to sea level yesterday Dec 7th. Thank you to Jim Kennedy for the photo.

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

A brief break in storms today will reduce the chance for naturally occurring avalanches. However, human triggered avalanches are a concern in the higher Alpine terrain above 2,500′ where new snow fell. Fresh wind slabs near ridgelines and in cross-loaded gullies should be expected. Slabs could be anywhere from only a few inches thick to over two feet, depending on the severity of windloading and the amount of new snow.

If planning to travel to these higher elevation slopes today, be sure to manage terrain wisely and keep a close lookout for how much snow fell, windloading patterns, how is the new snow bonding with the old snow surface and do you see any cracking in the snow around you. Quick hand pits will be a good way to assess this.

Cornices: Fresh cornices are likely to break off easily and may trigger an avalanche below.

Avalanche Problem 2

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

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

The high elevation snowpack, over 3,000′, remains a concern due to a layer of faceted weak snow over a hard crust near the bottom of the snowpack. With new snow yesterday, and more on the way tonight and tomorrow, we are watching to see if this weak layer becomes overloaded and results in larger avalanches that break near the ground. This is something to pay attention to if traveling up to these higher elevations during today’s break in storms.

Weather

Sun, December 8th, 2019

Yesterday: Cloudy skies with rain falling as high as 2,000′ at times. Girdwood Valley saw around 1.5″ of rain, which equates to around 15″ of snow at the high elevations. Turnagain Pass only saw .6 to .8″ of rain with 6-8″ of snow in the higher terrain. Ridgetop winds were strong from the east, 25-40mph averages with gusts to 79mph. Temperatures bumped to 40F at 1,000′ and the upper 20’sF at 4,000′ last night before slightly cooling this morning.

Today: A break in storms is expected today. We should see partly cloudy skies and light to moderate easterly ridgetop winds (10-25mph). Temperatures will remain warm, in the mid 30’sF at 1,000′ and mid 20’sF along ridgelines. The next storm will move in tonight with heavy rain and strong winds. Up to an inch of rain is forecast overnight (snow above 2,000′) with ridgetop winds picking to the 40-50mph range with much stronger gusts.

Tomorrow: Heavy rain, strong wind and stormy weather should continue through the day and into Tuesday morning. Models are showing this second system bringing 3-5″ of rain below 2,000′ and several feet of snow to the high elevations. At this point, the rain line looks to hover near 2,000′ and could jump up to 3,000′ for periods. Stay tuned!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	35	3	0.6	19
Summit Lake (1400′)	35	rain	0.3	9
Alyeska Mid (1700′)	34	5	1.5	22

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	26	NE	31	79
Seattle Ridge (2400′)	N/A*	N/A*	N/A*	N/A*

*Seattle Ridge anemometer (wind sensor) is rimed over and the temperature sensor is not functioning. A new temperature sensor is arriving soon and we hope to get it up on the next clear day.

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.