Sat, March 07, 2020 Turnagain Pass Avalanche Forecast

Sat, March 7th, 2020

Alpine
Above 2,500'

Moderate (2)

Treeline
1,000'-2,500'

Moderate (2)

Below Treeline
Below 1,000'

Moderate (2)

Alpine Above 2,500'		Moderate (2)
Treeline 1,000'-2,500'		Moderate (2)
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

Wind Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

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

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

Cloudy skies have moved in over the region, brought temperatures up to a more habitable 20-25°F and even a few snow flurries have fallen this morning. With a relatively weak weather system moving through this weekend, it looks as though our forecast zone will see an inch or so of snow today, 2″ tonight and up to an additional 4″ by tomorrow. This is a pretty meager ‘re-fresh’ and that said, it will be old and new wind slabs that will be our main avalanche concerns.

Lingering wind slabs from last week’s outflow wind event may still be possible to trigger. These wind slabs could propagate further than expected and could also step down into buried weak layers. This was the case with the Lynx Creek avalanche that occurred Thursday. In case you missed it, those details are HERE. These older wind slabs could be sitting on buried surface hoar, making them take longer to bond and why they could break out wider than one might think.

Fresh wind slabs are also something to look for today in upper elevation terrain. Ridgetop winds may reach averages of 20mph from the east. This will be enough to transport loose snow and load slopes, if the loose snow is available. If you are headed out today, watch for wind textured surfaces, hollow feeling snow and stiffer snow over softer snow. These are all signs of a wind slab. These slabs are likely to be around a foot thick. Quick hand pits are also good ways to suss out a wind slab. If you find one in your hand pit, look close, you may see some buried surface hoar feathers under it.

Wind textured surfaces along the Southeast face of Seattle Ridge at Turnagain Pass on Thursday. 3.5.20.

Wind loaded slopes on Colorado Peak in the Summit Lake area along with a very wide propagating natural slab avalanche lower on the slope. This also occurred also on Thursday. 3.5.20. Photo: Alex McLain

Avalanche Problem 2

Deep Persistent Slabs
Almost Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

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

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

It is still important to remember that weak faceted snow from January sits 3 to 6 feet deep in the snowpack. The wind slab triggered in Lynx Creek two days ago was a larger avalanche because it ‘stepped down’ into these old weak layers. Not only can this happen again, but it is possible a person triggers the deep layer from the start. As we know, with time the likelihood of triggering a deep slab is decreasing, but we have too much proof to write this problem off. Keeping our terrain choices in line with the ‘what if I trigger a large slab’ question remains prudent.

Cornices: As always, avoid travel on or underneath cornices.

Loose snow avalanches: In areas that were protected from the wind, sluffs are possible in steep terrain.

Weather

Sat, March 7th, 2020

Yesterday: Partly cloudy to overcast skies filled the region. Ridgetop winds were light to moderate from the east (5-15mph) with Sunburst gusting to 29mph yesterday morning. Temperatures rose into the 20’s°F at most locations from sea level to ridgetops.

Today: A weather system is moving in and brining cloudy skies and light snow showers to the forecast area. Only a trace to an inch of accumulation is expected today with 2″ of new snow possible tonight. Ridgetop winds are forecast to remain easterly and blowing in the 10-20mph range. Temperatures will remain in the 20°’F at all elevations.

Tomorrow: Snowfall will continue tomorrow with an additional 2-4″ and up to 6″ or more in favored area likely near the coast. Ridgetop winds are slated to increase to the 15-25mph range along with the peak of snowfall looking to occur mid-day. Temperatures look to say in the mid to upper 20’s°F with snow to sea level.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	21	0	0	71
Summit Lake (1400′)	18	0	0	31
Alyeska Mid (1700′)	20	trace	trace	80

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	13	NE	9	29
Seattle Ridge (2400′)	17	SE	7	17

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.