Thu, April 18, 2019 Turnagain Pass Avalanche Forecast

Thu, April 18th, 2019

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Low (1)

Below Treeline
Below 1,000'

No Rating (0)

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

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

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

Yesterday was cloudy with very light showers throughout the day and a total of an inch of snow falling in the last 24 hrs. Rain/snowline was observed to be around 1600′. Today is forecast to be slightly cooler with the potential for another inch or two of snow. The main avalanche concern continues to be shaded aspects in the Alpine above 3,000′, where a weak layer of facets and buried surface hoar exists 1-2′ below the surface. A layer of buried surface hoar was the culprit in two human triggered avalanches over the weekend in Seattle Creek. Both of these avalanches occurred at 3200’ on North aspects and released on a layer of buried surface hoar sitting on a melt freeze crust. One of these avalanches was triggered at the top of a chute. The other avalanche we suspect was remote triggered from 5-10’ away. In both incidents no one was caught. On Monday an observer reported whumping and found a weak layer of facets in a hand pit in higher elevations above Girdwood. Approach high northerly slopes with caution. Look for signs of instability and stick to safe travel protocol: evaluate terrain for consequences, expose one person a time, watch partners and have an escape route planned.

Additional Concerns:

STORM SLABS: Tonight into tomorrow 5-10″ of snow is forecast to fall to sea level. The snow that fell yesterday covered a variety of surfaces including a new layer of surface hoar. Friday it will be important to pay attention to how much snow has fallen, how well the new snow is bonding to the old snow surfaces and look for signs of instability. More snow will = thicker storm slab!

CORNICES: There are still large cornices along ridge tops. Give them lots of space as they can break farther back than expected.

GLIDE AVALANCHES: It’s been almost two weeks since our last known glide avalanche, but keep in mind glide cracks are continuing to creep down-hill. As always identify cracks and avoid traveling under their runout. They are unpredictable and can avalanche at any time.

WET LOOSE: If the sun comes out at some point after more snow falls look for small wet loose activity.

Snowboarder triggered avalanche in Warmup/-1 Bowl that occurred on Sunday.

Crown of the avalanche that also occurred over the weekend in Triangle/-2 Bowl. The weak layer was buried surface hoar sitting on a melt-freeze crust.

Weather

Thu, April 18th, 2019

Yesterday: Skies were mostly cloudy with light rain/snow showers throughout the day. Rain/snowline fluctuated around 1600′. Temperatures were in the mid to high 20Fs at ridgetops and mid to high 30Fs at lower elevations. Winds were easterly 5-15 mph gusting into the 20s. Overnight temperatures dipped into the low 20Fs and 30Fs and winds became light and northerly.

Today: Mostly cloudy skies and light rain/snow showers, 1-2″ of snow throughout the day. Rain/snowline is forecast to be around 1000′. Temperatures are forecast to be in the 20Fs to low 30Fs. Winds will be northerly 5-15 mph with gusts into the 20s. Tonight temperatures will be in the 20Fs. Snow is expected to fall to sea level with 5-10″ overnight into tomorrow. Winds will remain northerly 5-15 mph with gusts into the 20s.

Tomorrow: Snow continues into tomorrow with another few inches of snow forecast. Winds shift to the east and temperatures stay in the 20Fs. The unsettled and more wintery pattern looks to continue into the weekend.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	1	0.1	62
Summit Lake (1400′)	34	1	0.1	18
Alyeska Mid (1700′)	34	1	0.1	55

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	28	NE	6	29
Seattle Ridge (2400′)	29	NE	5	15

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.