Tue, December 22, 2020 Turnagain Pass Avalanche Forecast

Tue, December 22nd, 2020

Alpine
Above 2,500'

High (4)

Treeline
1,000'-2,500'

High (4)

Below Treeline
Below 1,000'

High (4)

Alpine Above 2,500'		High (4)
Treeline 1,000'-2,500'		High (4)
Below Treeline Below 1,000'		High (4)

Danger Scale:

No Rating (0)

Low (1)

Moderate (2)

Considerable (3)

High (4)

Extreme (5)

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

The weather has gone into overdrive, and we are expecting a lot of avalanche activity today. With heavy snowfall, strong winds, and the rain level creeping up higher through the day, we are anticipating large natural avalanches anywhere from 3-6′ deep, and human-triggered avalanches will be very likely. Ridgetop winds have been blowing 49 to 66 mph since 1:00 this morning, with gusts as high as 104 mph, and the strongest period is expected to continue through the middle of the day. By the time this system passes tomorrow, we could see over 4′ of snow in higher elevation start zones, equaling 4-5″ snow water equivalent (SWE). Temperatures will continue to rise through the day, bringing the rain level as high as 1700′, with as much as 4″ rain on snow at lower elevations below 1000′ before temperatures cool down early tomorrow morning. As heavy snowfall and strong winds will be loading up start zones, rain will be increasing the likelihood of wet avalanches at lower elevations. With all of this active weather, we are anticipating large avalanches that could run far into lower elevation runout zones.

Gusts have reached 104 mph at Sunburst this morning.

NWS graphic showing predicted water content for this storm- over 5″ water at Turnagain Pass!

While we will likely see some impressive avalanches failing within the new snow, there is also the smaller possibility of deeper weak layers in the snowpack failing under the weight of all of this new snow (and rain), which could make for some really, really big avalanches. These weak layers have gained strength, and they have not been reactive in over two weeks. But 4” of SWE in less than 24 hours will sure be a good test to see just how strong they have become. The weather is wild, but that actually makes the avalanche situation quite simple. Today, avalanche conditions will be very dangerous, and travel in avalanche terrain is not recommended.

Glide Avalanches: As if we didn’t already have enough action, we saw our first reported glide avalanche of the season yesterday on Gilpatrick Mountain in the Summit Lake area. This is going to be another issue we will be keeping an eye on as the dust settles from this storm.

Weather

Tue, December 22nd, 2020

Yesterday: After a calm morning, ridgetop winds started picking up at noon, blowing 15-20 mph with gusts into the 30s out of the east. Temperatures climbed from the mid-teens to the low 30’s F at upper elevations, reaching the high 30’s F and even 40 F at lower elevations. Light flurries moved in later in the afternoon.

Today: Easterly winds continued to pick up overnight, blowing 49 – 66 mph since 1:00 this morning with gusts as high as 104 mph. The strongest period of winds is expected to continue through late this morning. We are anticipating up to 4′ of snow at upper elevations, equaling 4″ water. Rain level is expected to creep up to 1700′, and we could see as much as 4″ of rain on snow at lower elevations. High elevation temperatures will reach the low 30’s F this evening, and lower elevations could see temperatures as high as 40 F.

Tomorrow: Snowfall will taper off tomorrow morning, with winds shifting to the south/southwest and dropping to 15-30 mph. Temperatures are expected to be in the mid- to upper 20’s F, and skies may start to clear later tomorrow afternoon and early tomorrow evening.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	4	0.6	63
Summit Lake (1400′)	27	3	0.3	29
Alyeska Mid (1700′)	26	6	0.5	64

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	18	ENE	30	104
Seattle Ridge (2400′)	20	SE	18	51

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 Mon, May 15th, 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	Open	Chugach NF staff will be assessing daily after May 15th. Please keep machines on the snow and avoid brown spots to keep this area open as long as possible.
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.